The Linux Kernel API¶
List Management Functions¶
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void
INIT_LIST_HEAD(struct list_head *list)¶ Initialize a list_head structure
Parameters
struct list_head *list- list_head structure to be initialized.
Description
Initializes the list_head to point to itself. If it is a list header, the result is an empty list.
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void
list_add(struct list_head *new, struct list_head *head)¶ add a new entry
Parameters
struct list_head *new- new entry to be added
struct list_head *head- list head to add it after
Description
Insert a new entry after the specified head. This is good for implementing stacks.
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void
list_add_tail(struct list_head *new, struct list_head *head)¶ add a new entry
Parameters
struct list_head *new- new entry to be added
struct list_head *head- list head to add it before
Description
Insert a new entry before the specified head. This is useful for implementing queues.
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void
list_del(struct list_head *entry)¶ deletes entry from list.
Parameters
struct list_head *entry- the element to delete from the list.
Note
list_empty() on entry does not return true after this, the entry is
in an undefined state.
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void
list_replace(struct list_head *old, struct list_head *new)¶ replace old entry by new one
Parameters
struct list_head *old- the element to be replaced
struct list_head *new- the new element to insert
Description
If old was empty, it will be overwritten.
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void
list_replace_init(struct list_head *old, struct list_head *new)¶ replace old entry by new one and initialize the old one
Parameters
struct list_head *old- the element to be replaced
struct list_head *new- the new element to insert
Description
If old was empty, it will be overwritten.
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void
list_swap(struct list_head *entry1, struct list_head *entry2)¶ replace entry1 with entry2 and re-add entry1 at entry2’s position
Parameters
struct list_head *entry1- the location to place entry2
struct list_head *entry2- the location to place entry1
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void
list_del_init(struct list_head *entry)¶ deletes entry from list and reinitialize it.
Parameters
struct list_head *entry- the element to delete from the list.
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void
list_move(struct list_head *list, struct list_head *head)¶ delete from one list and add as another’s head
Parameters
struct list_head *list- the entry to move
struct list_head *head- the head that will precede our entry
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void
list_move_tail(struct list_head *list, struct list_head *head)¶ delete from one list and add as another’s tail
Parameters
struct list_head *list- the entry to move
struct list_head *head- the head that will follow our entry
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void
list_bulk_move_tail(struct list_head *head, struct list_head *first, struct list_head *last)¶ move a subsection of a list to its tail
Parameters
struct list_head *head- the head that will follow our entry
struct list_head *first- first entry to move
struct list_head *last- last entry to move, can be the same as first
Description
Move all entries between first and including last before head. All three entries must belong to the same linked list.
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int
list_is_first(const struct list_head *list, const struct list_head *head)¶ - tests whether list is the first entry in list head
Parameters
const struct list_head *list- the entry to test
const struct list_head *head- the head of the list
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int
list_is_last(const struct list_head *list, const struct list_head *head)¶ tests whether list is the last entry in list head
Parameters
const struct list_head *list- the entry to test
const struct list_head *head- the head of the list
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int
list_empty(const struct list_head *head)¶ tests whether a list is empty
Parameters
const struct list_head *head- the list to test.
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void
list_del_init_careful(struct list_head *entry)¶ deletes entry from list and reinitialize it.
Parameters
struct list_head *entry- the element to delete from the list.
Description
This is the same as list_del_init(), except designed to be used
together with list_empty_careful() in a way to guarantee ordering
of other memory operations.
Any memory operations done before a list_del_init_careful() are
guaranteed to be visible after a list_empty_careful() test.
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int
list_empty_careful(const struct list_head *head)¶ tests whether a list is empty and not being modified
Parameters
const struct list_head *head- the list to test
Description
tests whether a list is empty _and_ checks that no other CPU might be in the process of modifying either member (next or prev)
NOTE
using list_empty_careful() without synchronization
can only be safe if the only activity that can happen
to the list entry is list_del_init(). Eg. it cannot be used
if another CPU could re-list_add() it.
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void
list_rotate_left(struct list_head *head)¶ rotate the list to the left
Parameters
struct list_head *head- the head of the list
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void
list_rotate_to_front(struct list_head *list, struct list_head *head)¶ Rotate list to specific item.
Parameters
struct list_head *list- The desired new front of the list.
struct list_head *head- The head of the list.
Description
Rotates list so that list becomes the new front of the list.
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int
list_is_singular(const struct list_head *head)¶ tests whether a list has just one entry.
Parameters
const struct list_head *head- the list to test.
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void
list_cut_position(struct list_head *list, struct list_head *head, struct list_head *entry)¶ cut a list into two
Parameters
struct list_head *list- a new list to add all removed entries
struct list_head *head- a list with entries
struct list_head *entry- an entry within head, could be the head itself and if so we won’t cut the list
Description
This helper moves the initial part of head, up to and including entry, from head to list. You should pass on entry an element you know is on head. list should be an empty list or a list you do not care about losing its data.
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void
list_cut_before(struct list_head *list, struct list_head *head, struct list_head *entry)¶ cut a list into two, before given entry
Parameters
struct list_head *list- a new list to add all removed entries
struct list_head *head- a list with entries
struct list_head *entry- an entry within head, could be the head itself
Description
This helper moves the initial part of head, up to but excluding entry, from head to list. You should pass in entry an element you know is on head. list should be an empty list or a list you do not care about losing its data. If entry == head, all entries on head are moved to list.
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void
list_splice(const struct list_head *list, struct list_head *head)¶ join two lists, this is designed for stacks
Parameters
const struct list_head *list- the new list to add.
struct list_head *head- the place to add it in the first list.
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void
list_splice_tail(struct list_head *list, struct list_head *head)¶ join two lists, each list being a queue
Parameters
struct list_head *list- the new list to add.
struct list_head *head- the place to add it in the first list.
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void
list_splice_init(struct list_head *list, struct list_head *head)¶ join two lists and reinitialise the emptied list.
Parameters
struct list_head *list- the new list to add.
struct list_head *head- the place to add it in the first list.
Description
The list at list is reinitialised
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void
list_splice_tail_init(struct list_head *list, struct list_head *head)¶ join two lists and reinitialise the emptied list
Parameters
struct list_head *list- the new list to add.
struct list_head *head- the place to add it in the first list.
Description
Each of the lists is a queue. The list at list is reinitialised
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list_entry(ptr, type, member)¶ get the struct for this entry
Parameters
ptr- the
struct list_headpointer. type- the type of the struct this is embedded in.
member- the name of the list_head within the struct.
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list_first_entry(ptr, type, member)¶ get the first element from a list
Parameters
ptr- the list head to take the element from.
type- the type of the struct this is embedded in.
member- the name of the list_head within the struct.
Description
Note, that list is expected to be not empty.
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list_last_entry(ptr, type, member)¶ get the last element from a list
Parameters
ptr- the list head to take the element from.
type- the type of the struct this is embedded in.
member- the name of the list_head within the struct.
Description
Note, that list is expected to be not empty.
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list_first_entry_or_null(ptr, type, member)¶ get the first element from a list
Parameters
ptr- the list head to take the element from.
type- the type of the struct this is embedded in.
member- the name of the list_head within the struct.
Description
Note that if the list is empty, it returns NULL.
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list_next_entry(pos, member)¶ get the next element in list
Parameters
pos- the type * to cursor
member- the name of the list_head within the struct.
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list_prev_entry(pos, member)¶ get the prev element in list
Parameters
pos- the type * to cursor
member- the name of the list_head within the struct.
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list_for_each(pos, head)¶ iterate over a list
Parameters
pos- the
struct list_headto use as a loop cursor. head- the head for your list.
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list_for_each_continue(pos, head)¶ continue iteration over a list
Parameters
pos- the
struct list_headto use as a loop cursor. head- the head for your list.
Description
Continue to iterate over a list, continuing after the current position.
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list_for_each_prev(pos, head)¶ iterate over a list backwards
Parameters
pos- the
struct list_headto use as a loop cursor. head- the head for your list.
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list_for_each_safe(pos, n, head)¶ iterate over a list safe against removal of list entry
Parameters
pos- the
struct list_headto use as a loop cursor. n- another
struct list_headto use as temporary storage head- the head for your list.
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list_for_each_prev_safe(pos, n, head)¶ iterate over a list backwards safe against removal of list entry
Parameters
pos- the
struct list_headto use as a loop cursor. n- another
struct list_headto use as temporary storage head- the head for your list.
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list_entry_is_head(pos, head, member)¶ test if the entry points to the head of the list
Parameters
pos- the type * to cursor
head- the head for your list.
member- the name of the list_head within the struct.
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list_for_each_entry(pos, head, member)¶ iterate over list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
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list_for_each_entry_reverse(pos, head, member)¶ iterate backwards over list of given type.
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
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list_prepare_entry(pos, head, member)¶ prepare a pos entry for use in
list_for_each_entry_continue()
Parameters
pos- the type * to use as a start point
head- the head of the list
member- the name of the list_head within the struct.
Description
Prepares a pos entry for use as a start point in list_for_each_entry_continue().
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list_for_each_entry_continue(pos, head, member)¶ continue iteration over list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
Description
Continue to iterate over list of given type, continuing after the current position.
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list_for_each_entry_continue_reverse(pos, head, member)¶ iterate backwards from the given point
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
Description
Start to iterate over list of given type backwards, continuing after the current position.
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list_for_each_entry_from(pos, head, member)¶ iterate over list of given type from the current point
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
Description
Iterate over list of given type, continuing from current position.
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list_for_each_entry_from_reverse(pos, head, member)¶ iterate backwards over list of given type from the current point
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
Description
Iterate backwards over list of given type, continuing from current position.
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list_for_each_entry_safe(pos, n, head, member)¶ iterate over list of given type safe against removal of list entry
Parameters
pos- the type * to use as a loop cursor.
n- another type * to use as temporary storage
head- the head for your list.
member- the name of the list_head within the struct.
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list_for_each_entry_safe_continue(pos, n, head, member)¶ continue list iteration safe against removal
Parameters
pos- the type * to use as a loop cursor.
n- another type * to use as temporary storage
head- the head for your list.
member- the name of the list_head within the struct.
Description
Iterate over list of given type, continuing after current point, safe against removal of list entry.
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list_for_each_entry_safe_from(pos, n, head, member)¶ iterate over list from current point safe against removal
Parameters
pos- the type * to use as a loop cursor.
n- another type * to use as temporary storage
head- the head for your list.
member- the name of the list_head within the struct.
Description
Iterate over list of given type from current point, safe against removal of list entry.
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list_for_each_entry_safe_reverse(pos, n, head, member)¶ iterate backwards over list safe against removal
Parameters
pos- the type * to use as a loop cursor.
n- another type * to use as temporary storage
head- the head for your list.
member- the name of the list_head within the struct.
Description
Iterate backwards over list of given type, safe against removal of list entry.
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list_safe_reset_next(pos, n, member)¶ reset a stale list_for_each_entry_safe loop
Parameters
pos- the loop cursor used in the list_for_each_entry_safe loop
n- temporary storage used in list_for_each_entry_safe
member- the name of the list_head within the struct.
Description
list_safe_reset_next is not safe to use in general if the list may be modified concurrently (eg. the lock is dropped in the loop body). An exception to this is if the cursor element (pos) is pinned in the list, and list_safe_reset_next is called after re-taking the lock and before completing the current iteration of the loop body.
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int
hlist_unhashed(const struct hlist_node *h)¶ Has node been removed from list and reinitialized?
Parameters
const struct hlist_node *h- Node to be checked
Description
Not that not all removal functions will leave a node in unhashed
state. For example, hlist_nulls_del_init_rcu() does leave the
node in unhashed state, but hlist_nulls_del() does not.
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int
hlist_unhashed_lockless(const struct hlist_node *h)¶ Version of hlist_unhashed for lockless use
Parameters
const struct hlist_node *h- Node to be checked
Description
This variant of hlist_unhashed() must be used in lockless contexts
to avoid potential load-tearing. The READ_ONCE() is paired with the
various WRITE_ONCE() in hlist helpers that are defined below.
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int
hlist_empty(const struct hlist_head *h)¶ Is the specified hlist_head structure an empty hlist?
Parameters
const struct hlist_head *h- Structure to check.
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void
hlist_del(struct hlist_node *n)¶ Delete the specified hlist_node from its list
Parameters
struct hlist_node *n- Node to delete.
Description
Note that this function leaves the node in hashed state. Use
hlist_del_init() or similar instead to unhash n.
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void
hlist_del_init(struct hlist_node *n)¶ Delete the specified hlist_node from its list and initialize
Parameters
struct hlist_node *n- Node to delete.
Description
Note that this function leaves the node in unhashed state.
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void
hlist_add_head(struct hlist_node *n, struct hlist_head *h)¶ add a new entry at the beginning of the hlist
Parameters
struct hlist_node *n- new entry to be added
struct hlist_head *h- hlist head to add it after
Description
Insert a new entry after the specified head. This is good for implementing stacks.
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void
hlist_add_before(struct hlist_node *n, struct hlist_node *next)¶ add a new entry before the one specified
Parameters
struct hlist_node *n- new entry to be added
struct hlist_node *next- hlist node to add it before, which must be non-NULL
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void
hlist_add_behind(struct hlist_node *n, struct hlist_node *prev)¶ add a new entry after the one specified
Parameters
struct hlist_node *n- new entry to be added
struct hlist_node *prev- hlist node to add it after, which must be non-NULL
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void
hlist_add_fake(struct hlist_node *n)¶ create a fake hlist consisting of a single headless node
Parameters
struct hlist_node *n- Node to make a fake list out of
Description
This makes n appear to be its own predecessor on a headless hlist.
The point of this is to allow things like hlist_del() to work correctly
in cases where there is no list.
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bool
hlist_fake(struct hlist_node *h)¶
Parameters
struct hlist_node *h- Node to check for being a self-referential fake hlist.
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bool
hlist_is_singular_node(struct hlist_node *n, struct hlist_head *h)¶ is node the only element of the specified hlist?
Parameters
struct hlist_node *n- Node to check for singularity.
struct hlist_head *h- Header for potentially singular list.
Description
Check whether the node is the only node of the head without accessing head, thus avoiding unnecessary cache misses.
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void
hlist_move_list(struct hlist_head *old, struct hlist_head *new)¶ Move an hlist
Parameters
struct hlist_head *old- hlist_head for old list.
struct hlist_head *new- hlist_head for new list.
Description
Move a list from one list head to another. Fixup the pprev reference of the first entry if it exists.
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hlist_for_each_entry(pos, head, member)¶ iterate over list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the hlist_node within the struct.
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hlist_for_each_entry_continue(pos, member)¶ iterate over a hlist continuing after current point
Parameters
pos- the type * to use as a loop cursor.
member- the name of the hlist_node within the struct.
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hlist_for_each_entry_from(pos, member)¶ iterate over a hlist continuing from current point
Parameters
pos- the type * to use as a loop cursor.
member- the name of the hlist_node within the struct.
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hlist_for_each_entry_safe(pos, n, head, member)¶ iterate over list of given type safe against removal of list entry
Parameters
pos- the type * to use as a loop cursor.
n- a
struct hlist_nodeto use as temporary storage head- the head for your list.
member- the name of the hlist_node within the struct.
Basic C Library Functions¶
When writing drivers, you cannot in general use routines which are from the C Library. Some of the functions have been found generally useful and they are listed below. The behaviour of these functions may vary slightly from those defined by ANSI, and these deviations are noted in the text.
String Conversions¶
-
unsigned long long
simple_strtoull(const char *cp, char **endp, unsigned int base)¶ convert a string to an unsigned long long
Parameters
const char *cp- The start of the string
char **endp- A pointer to the end of the parsed string will be placed here
unsigned int base- The number base to use
Description
This function has caveats. Please use kstrtoull instead.
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unsigned long
simple_strtoul(const char *cp, char **endp, unsigned int base)¶ convert a string to an unsigned long
Parameters
const char *cp- The start of the string
char **endp- A pointer to the end of the parsed string will be placed here
unsigned int base- The number base to use
Description
This function has caveats. Please use kstrtoul instead.
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long
simple_strtol(const char *cp, char **endp, unsigned int base)¶ convert a string to a signed long
Parameters
const char *cp- The start of the string
char **endp- A pointer to the end of the parsed string will be placed here
unsigned int base- The number base to use
Description
This function has caveats. Please use kstrtol instead.
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long long
simple_strtoll(const char *cp, char **endp, unsigned int base)¶ convert a string to a signed long long
Parameters
const char *cp- The start of the string
char **endp- A pointer to the end of the parsed string will be placed here
unsigned int base- The number base to use
Description
This function has caveats. Please use kstrtoll instead.
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int
vsnprintf(char *buf, size_t size, const char *fmt, va_list args)¶ Format a string and place it in a buffer
Parameters
char *buf- The buffer to place the result into
size_t size- The size of the buffer, including the trailing null space
const char *fmt- The format string to use
va_list args- Arguments for the format string
Description
This function generally follows C99 vsnprintf, but has some extensions and a few limitations:
``n``is unsupported``p``*is handled by pointer()
See pointer() or How to get printk format specifiers right for more extensive description.
Please update the documentation in both places when making changes
The return value is the number of characters which would
be generated for the given input, excluding the trailing
‘0’, as per ISO C99. If you want to have the exact
number of characters written into buf as return value
(not including the trailing ‘0’), use vscnprintf(). If the
return is greater than or equal to size, the resulting
string is truncated.
If you’re not already dealing with a va_list consider using snprintf().
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int
vscnprintf(char *buf, size_t size, const char *fmt, va_list args)¶ Format a string and place it in a buffer
Parameters
char *buf- The buffer to place the result into
size_t size- The size of the buffer, including the trailing null space
const char *fmt- The format string to use
va_list args- Arguments for the format string
Description
The return value is the number of characters which have been written into the buf not including the trailing ‘0’. If size is == 0 the function returns 0.
If you’re not already dealing with a va_list consider using scnprintf().
See the vsnprintf() documentation for format string extensions over C99.
-
int
snprintf(char *buf, size_t size, const char *fmt, ...)¶ Format a string and place it in a buffer
Parameters
char *buf- The buffer to place the result into
size_t size- The size of the buffer, including the trailing null space
const char *fmt- The format string to use
...- Arguments for the format string
Description
The return value is the number of characters which would be generated for the given input, excluding the trailing null, as per ISO C99. If the return is greater than or equal to size, the resulting string is truncated.
See the vsnprintf() documentation for format string extensions over C99.
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int
scnprintf(char *buf, size_t size, const char *fmt, ...)¶ Format a string and place it in a buffer
Parameters
char *buf- The buffer to place the result into
size_t size- The size of the buffer, including the trailing null space
const char *fmt- The format string to use
...- Arguments for the format string
Description
The return value is the number of characters written into buf not including the trailing ‘0’. If size is == 0 the function returns 0.
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int
vsprintf(char *buf, const char *fmt, va_list args)¶ Format a string and place it in a buffer
Parameters
char *buf- The buffer to place the result into
const char *fmt- The format string to use
va_list args- Arguments for the format string
Description
The function returns the number of characters written
into buf. Use vsnprintf() or vscnprintf() in order to avoid
buffer overflows.
If you’re not already dealing with a va_list consider using sprintf().
See the vsnprintf() documentation for format string extensions over C99.
-
int
sprintf(char *buf, const char *fmt, ...)¶ Format a string and place it in a buffer
Parameters
char *buf- The buffer to place the result into
const char *fmt- The format string to use
...- Arguments for the format string
Description
The function returns the number of characters written
into buf. Use snprintf() or scnprintf() in order to avoid
buffer overflows.
See the vsnprintf() documentation for format string extensions over C99.
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int
vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args)¶ Parse a format string and place args’ binary value in a buffer
Parameters
u32 *bin_buf- The buffer to place args’ binary value
size_t size- The size of the buffer(by words(32bits), not characters)
const char *fmt- The format string to use
va_list args- Arguments for the format string
Description
The format follows C99 vsnprintf, except n is ignored, and its argument
is skipped.
The return value is the number of words(32bits) which would be generated for the given input.
NOTE
If the return value is greater than size, the resulting bin_buf is NOT
valid for bstr_printf().
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int
bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf)¶ Format a string from binary arguments and place it in a buffer
Parameters
char *buf- The buffer to place the result into
size_t size- The size of the buffer, including the trailing null space
const char *fmt- The format string to use
const u32 *bin_buf- Binary arguments for the format string
Description
This function like C99 vsnprintf, but the difference is that vsnprintf gets arguments from stack, and bstr_printf gets arguments from bin_buf which is a binary buffer that generated by vbin_printf.
- The format follows C99 vsnprintf, but has some extensions:
- see vsnprintf comment for details.
The return value is the number of characters which would
be generated for the given input, excluding the trailing
‘0’, as per ISO C99. If you want to have the exact
number of characters written into buf as return value
(not including the trailing ‘0’), use vscnprintf(). If the
return is greater than or equal to size, the resulting
string is truncated.
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int
bprintf(u32 *bin_buf, size_t size, const char *fmt, ...)¶ Parse a format string and place args’ binary value in a buffer
Parameters
u32 *bin_buf- The buffer to place args’ binary value
size_t size- The size of the buffer(by words(32bits), not characters)
const char *fmt- The format string to use
...- Arguments for the format string
Description
The function returns the number of words(u32) written into bin_buf.
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int
vsscanf(const char *buf, const char *fmt, va_list args)¶ Unformat a buffer into a list of arguments
Parameters
const char *buf- input buffer
const char *fmt- format of buffer
va_list args- arguments
-
int
sscanf(const char *buf, const char *fmt, ...)¶ Unformat a buffer into a list of arguments
Parameters
const char *buf- input buffer
const char *fmt- formatting of buffer
...- resulting arguments
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int
kstrtol(const char *s, unsigned int base, long *res)¶ convert a string to a long
Parameters
const char *s- The start of the string. The string must be null-terminated, and may also include a single newline before its terminating null. The first character may also be a plus sign or a minus sign.
unsigned int base- The number base to use. The maximum supported base is 16. If base is given as 0, then the base of the string is automatically detected with the conventional semantics - If it begins with 0x the number will be parsed as a hexadecimal (case insensitive), if it otherwise begins with 0, it will be parsed as an octal number. Otherwise it will be parsed as a decimal.
long *res- Where to write the result of the conversion on success.
Description
Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
Preferred over simple_strtol(). Return code must be checked.
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int
kstrtoul(const char *s, unsigned int base, unsigned long *res)¶ convert a string to an unsigned long
Parameters
const char *s- The start of the string. The string must be null-terminated, and may also include a single newline before its terminating null. The first character may also be a plus sign, but not a minus sign.
unsigned int base- The number base to use. The maximum supported base is 16. If base is given as 0, then the base of the string is automatically detected with the conventional semantics - If it begins with 0x the number will be parsed as a hexadecimal (case insensitive), if it otherwise begins with 0, it will be parsed as an octal number. Otherwise it will be parsed as a decimal.
unsigned long *res- Where to write the result of the conversion on success.
Description
Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
Preferred over simple_strtoul(). Return code must be checked.
-
int
kstrtoull(const char *s, unsigned int base, unsigned long long *res)¶ convert a string to an unsigned long long
Parameters
const char *s- The start of the string. The string must be null-terminated, and may also include a single newline before its terminating null. The first character may also be a plus sign, but not a minus sign.
unsigned int base- The number base to use. The maximum supported base is 16. If base is given as 0, then the base of the string is automatically detected with the conventional semantics - If it begins with 0x the number will be parsed as a hexadecimal (case insensitive), if it otherwise begins with 0, it will be parsed as an octal number. Otherwise it will be parsed as a decimal.
unsigned long long *res- Where to write the result of the conversion on success.
Description
Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
Preferred over simple_strtoull(). Return code must be checked.
-
int
kstrtoll(const char *s, unsigned int base, long long *res)¶ convert a string to a long long
Parameters
const char *s- The start of the string. The string must be null-terminated, and may also include a single newline before its terminating null. The first character may also be a plus sign or a minus sign.
unsigned int base- The number base to use. The maximum supported base is 16. If base is given as 0, then the base of the string is automatically detected with the conventional semantics - If it begins with 0x the number will be parsed as a hexadecimal (case insensitive), if it otherwise begins with 0, it will be parsed as an octal number. Otherwise it will be parsed as a decimal.
long long *res- Where to write the result of the conversion on success.
Description
Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
Preferred over simple_strtoll(). Return code must be checked.
-
int
kstrtouint(const char *s, unsigned int base, unsigned int *res)¶ convert a string to an unsigned int
Parameters
const char *s- The start of the string. The string must be null-terminated, and may also include a single newline before its terminating null. The first character may also be a plus sign, but not a minus sign.
unsigned int base- The number base to use. The maximum supported base is 16. If base is given as 0, then the base of the string is automatically detected with the conventional semantics - If it begins with 0x the number will be parsed as a hexadecimal (case insensitive), if it otherwise begins with 0, it will be parsed as an octal number. Otherwise it will be parsed as a decimal.
unsigned int *res- Where to write the result of the conversion on success.
Description
Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
Preferred over simple_strtoul(). Return code must be checked.
-
int
kstrtoint(const char *s, unsigned int base, int *res)¶ convert a string to an int
Parameters
const char *s- The start of the string. The string must be null-terminated, and may also include a single newline before its terminating null. The first character may also be a plus sign or a minus sign.
unsigned int base- The number base to use. The maximum supported base is 16. If base is given as 0, then the base of the string is automatically detected with the conventional semantics - If it begins with 0x the number will be parsed as a hexadecimal (case insensitive), if it otherwise begins with 0, it will be parsed as an octal number. Otherwise it will be parsed as a decimal.
int *res- Where to write the result of the conversion on success.
Description
Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
Preferred over simple_strtol(). Return code must be checked.
-
int
kstrtobool(const char *s, bool *res)¶ convert common user inputs into boolean values
Parameters
const char *s- input string
bool *res- result
Description
This routine returns 0 iff the first character is one of ‘Yy1Nn0’, or [oO][NnFf] for “on” and “off”. Otherwise it will return -EINVAL. Value pointed to by res is updated upon finding a match.
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void
string_get_size(u64 size, u64 blk_size, const enum string_size_units units, char *buf, int len)¶ get the size in the specified units
Parameters
u64 size- The size to be converted in blocks
u64 blk_size- Size of the block (use 1 for size in bytes)
const enum string_size_units units- units to use (powers of 1000 or 1024)
char *buf- buffer to format to
int len- length of buffer
Description
This function returns a string formatted to 3 significant figures giving the size in the required units. buf should have room for at least 9 bytes and will always be zero terminated.
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int
string_unescape(char *src, char *dst, size_t size, unsigned int flags)¶ unquote characters in the given string
Parameters
char *src- source buffer (escaped)
char *dst- destination buffer (unescaped)
size_t size- size of the destination buffer (0 to unlimit)
unsigned int flags- combination of the flags.
Description
The function unquotes characters in the given string.
Because the size of the output will be the same as or less than the size of the input, the transformation may be performed in place.
Caller must provide valid source and destination pointers. Be aware that destination buffer will always be NULL-terminated. Source string must be NULL-terminated as well. The supported flags are:
UNESCAPE_SPACE:
'\f' - form feed
'\n' - new line
'\r' - carriage return
'\t' - horizontal tab
'\v' - vertical tab
UNESCAPE_OCTAL:
'\NNN' - byte with octal value NNN (1 to 3 digits)
UNESCAPE_HEX:
'\xHH' - byte with hexadecimal value HH (1 to 2 digits)
UNESCAPE_SPECIAL:
'\"' - double quote
'\\' - backslash
'\a' - alert (BEL)
'\e' - escape
UNESCAPE_ANY:
all previous together
Return
The amount of the characters processed to the destination buffer excluding trailing ‘0’ is returned.
-
int
string_escape_mem(const char *src, size_t isz, char *dst, size_t osz, unsigned int flags, const char *only)¶ quote characters in the given memory buffer
Parameters
const char *src- source buffer (unescaped)
size_t isz- source buffer size
char *dst- destination buffer (escaped)
size_t osz- destination buffer size
unsigned int flags- combination of the flags
const char *only- NULL-terminated string containing characters used to limit the selected escape class. If characters are included in only that would not normally be escaped by the classes selected in flags, they will be copied to dst unescaped.
Description
The process of escaping byte buffer includes several parts. They are applied in the following sequence.
- The character is matched to the printable class, if asked, and in case of match it passes through to the output.
- The character is not matched to the one from only string and thus must go as-is to the output.
- The character is checked if it falls into the class given by flags.
ESCAPE_OCTALandESCAPE_HEXare going last since they cover any character. Note that they actually can’t go together, otherwiseESCAPE_HEXwill be ignored.
Caller must provide valid source and destination pointers. Be aware that destination buffer will not be NULL-terminated, thus caller have to append it if needs. The supported flags are:
%ESCAPE_SPACE: (special white space, not space itself)
'\f' - form feed
'\n' - new line
'\r' - carriage return
'\t' - horizontal tab
'\v' - vertical tab
%ESCAPE_SPECIAL:
'\\' - backslash
'\a' - alert (BEL)
'\e' - escape
%ESCAPE_NULL:
'\0' - null
%ESCAPE_OCTAL:
'\NNN' - byte with octal value NNN (3 digits)
%ESCAPE_ANY:
all previous together
%ESCAPE_NP:
escape only non-printable characters (checked by isprint)
%ESCAPE_ANY_NP:
all previous together
%ESCAPE_HEX:
'\xHH' - byte with hexadecimal value HH (2 digits)
Return
The total size of the escaped output that would be generated for the given input and flags. To check whether the output was truncated, compare the return value to osz. There is room left in dst for a ‘0’ terminator if and only if ret < osz.
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void
kfree_strarray(char **array, size_t n)¶ free a number of dynamically allocated strings contained in an array and the array itself
Parameters
char **array- Dynamically allocated array of strings to free.
size_t n- Number of strings (starting from the beginning of the array) to free.
Description
Passing a non-NULL array and n == 0 as well as NULL array are valid use-cases. If array is NULL, the function does nothing.
String Manipulation¶
-
int
strncasecmp(const char *s1, const char *s2, size_t len)¶ Case insensitive, length-limited string comparison
Parameters
const char *s1- One string
const char *s2- The other string
size_t len- the maximum number of characters to compare
-
char *
strcpy(char *dest, const char *src)¶ Copy a
NULterminated string
Parameters
char *dest- Where to copy the string to
const char *src- Where to copy the string from
-
char *
strncpy(char *dest, const char *src, size_t count)¶ Copy a length-limited, C-string
Parameters
char *dest- Where to copy the string to
const char *src- Where to copy the string from
size_t count- The maximum number of bytes to copy
Description
The result is not NUL-terminated if the source exceeds
count bytes.
In the case where the length of src is less than that of
count, the remainder of dest will be padded with NUL.
-
size_t
strlcpy(char *dest, const char *src, size_t size)¶ Copy a C-string into a sized buffer
Parameters
char *dest- Where to copy the string to
const char *src- Where to copy the string from
size_t size- size of destination buffer
Description
Compatible with *BSD: the result is always a valid
NUL-terminated string that fits in the buffer (unless,
of course, the buffer size is zero). It does not pad
out the result like strncpy() does.
-
ssize_t
strscpy(char *dest, const char *src, size_t count)¶ Copy a C-string into a sized buffer
Parameters
char *dest- Where to copy the string to
const char *src- Where to copy the string from
size_t count- Size of destination buffer
Description
Copy the string, or as much of it as fits, into the dest buffer. The behavior is undefined if the string buffers overlap. The destination buffer is always NUL terminated, unless it’s zero-sized.
Preferred to strlcpy() since the API doesn’t require reading memory
from the src string beyond the specified “count” bytes, and since
the return value is easier to error-check than strlcpy()’s.
In addition, the implementation is robust to the string changing out
from underneath it, unlike the current strlcpy() implementation.
Preferred to strncpy() since it always returns a valid string, and
doesn’t unnecessarily force the tail of the destination buffer to be
zeroed. If zeroing is desired please use strscpy_pad().
Return
- The number of characters copied (not including the trailing
NUL) - -E2BIG if count is 0 or src was truncated.
-
ssize_t
strscpy_pad(char *dest, const char *src, size_t count)¶ Copy a C-string into a sized buffer
Parameters
char *dest- Where to copy the string to
const char *src- Where to copy the string from
size_t count- Size of destination buffer
Description
Copy the string, or as much of it as fits, into the dest buffer. The
behavior is undefined if the string buffers overlap. The destination
buffer is always NUL terminated, unless it’s zero-sized.
If the source string is shorter than the destination buffer, zeros the tail of the destination buffer.
For full explanation of why you may want to consider using the
‘strscpy’ functions please see the function docstring for strscpy().
Return
- The number of characters copied (not including the trailing
NUL) - -E2BIG if count is 0 or src was truncated.
-
char *
stpcpy(char *__restrict__ dest, const char *__restrict__ src)¶ copy a string from src to dest returning a pointer to the new end of dest, including src’s
NUL-terminator. May overrun dest.
Parameters
char *__restrict__ dest- pointer to end of string being copied into. Must be large enough to receive copy.
const char *__restrict__ src- pointer to the beginning of string being copied from. Must not overlap dest.
Description
stpcpy differs from strcpy in a key way: the return value is a pointer
to the new NUL-terminating character in dest. (For strcpy, the return
value is a pointer to the start of dest). This interface is considered
unsafe as it doesn’t perform bounds checking of the inputs. As such it’s
not recommended for usage. Instead, its definition is provided in case
the compiler lowers other libcalls to stpcpy.
-
char *
strcat(char *dest, const char *src)¶ Append one
NUL-terminatedstring to another
Parameters
char *dest- The string to be appended to
const char *src- The string to append to it
-
char *
strncat(char *dest, const char *src, size_t count)¶ Append a length-limited, C-string to another
Parameters
char *dest- The string to be appended to
const char *src- The string to append to it
size_t count- The maximum numbers of bytes to copy
Description
Note that in contrast to strncpy(), strncat() ensures the result is
terminated.
-
size_t
strlcat(char *dest, const char *src, size_t count)¶ Append a length-limited, C-string to another
Parameters
char *dest- The string to be appended to
const char *src- The string to append to it
size_t count- The size of the destination buffer.
-
int
strcmp(const char *cs, const char *ct)¶ Compare two strings
Parameters
const char *cs- One string
const char *ct- Another string
-
int
strncmp(const char *cs, const char *ct, size_t count)¶ Compare two length-limited strings
Parameters
const char *cs- One string
const char *ct- Another string
size_t count- The maximum number of bytes to compare
-
char *
strchr(const char *s, int c)¶ Find the first occurrence of a character in a string
Parameters
const char *s- The string to be searched
int c- The character to search for
Description
Note that the NUL-terminator is considered part of the string, and can
be searched for.
-
char *
strchrnul(const char *s, int c)¶ Find and return a character in a string, or end of string
Parameters
const char *s- The string to be searched
int c- The character to search for
Description
Returns pointer to first occurrence of ‘c’ in s. If c is not found, then return a pointer to the null byte at the end of s.
-
char *
strrchr(const char *s, int c)¶ Find the last occurrence of a character in a string
Parameters
const char *s- The string to be searched
int c- The character to search for
-
char *
strnchr(const char *s, size_t count, int c)¶ Find a character in a length limited string
Parameters
const char *s- The string to be searched
size_t count- The number of characters to be searched
int c- The character to search for
Description
Note that the NUL-terminator is considered part of the string, and can
be searched for.
-
char *
skip_spaces(const char *str)¶ Removes leading whitespace from str.
Parameters
const char *str- The string to be stripped.
Description
Returns a pointer to the first non-whitespace character in str.
-
char *
strim(char *s)¶ Removes leading and trailing whitespace from s.
Parameters
char *s- The string to be stripped.
Description
Note that the first trailing whitespace is replaced with a NUL-terminator
in the given string s. Returns a pointer to the first non-whitespace
character in s.
-
size_t
strlen(const char *s)¶ Find the length of a string
Parameters
const char *s- The string to be sized
-
size_t
strnlen(const char *s, size_t count)¶ Find the length of a length-limited string
Parameters
const char *s- The string to be sized
size_t count- The maximum number of bytes to search
-
size_t
strspn(const char *s, const char *accept)¶ Calculate the length of the initial substring of s which only contain letters in accept
Parameters
const char *s- The string to be searched
const char *accept- The string to search for
-
size_t
strcspn(const char *s, const char *reject)¶ Calculate the length of the initial substring of s which does not contain letters in reject
Parameters
const char *s- The string to be searched
const char *reject- The string to avoid
-
char *
strpbrk(const char *cs, const char *ct)¶ Find the first occurrence of a set of characters
Parameters
const char *cs- The string to be searched
const char *ct- The characters to search for
-
char *
strsep(char **s, const char *ct)¶ Split a string into tokens
Parameters
char **s- The string to be searched
const char *ct- The characters to search for
Description
strsep() updates s to point after the token, ready for the next call.
It returns empty tokens, too, behaving exactly like the libc function of that name. In fact, it was stolen from glibc2 and de-fancy-fied. Same semantics, slimmer shape. ;)
-
bool
sysfs_streq(const char *s1, const char *s2)¶ return true if strings are equal, modulo trailing newline
Parameters
const char *s1- one string
const char *s2- another string
Description
This routine returns true iff two strings are equal, treating both NUL and newline-then-NUL as equivalent string terminations. It’s geared for use with sysfs input strings, which generally terminate with newlines but are compared against values without newlines.
-
int
match_string(const char * const *array, size_t n, const char *string)¶ matches given string in an array
Parameters
const char * const *array- array of strings
size_t n- number of strings in the array or -1 for NULL terminated arrays
const char *string- string to match with
Description
This routine will look for a string in an array of strings up to the n-th element in the array or until the first NULL element.
Historically the value of -1 for n, was used to search in arrays that are NULL terminated. However, the function does not make a distinction when finishing the search: either n elements have been compared OR the first NULL element was found.
Return
index of a string in the array if matches, or -EINVAL otherwise.
-
int
__sysfs_match_string(const char * const *array, size_t n, const char *str)¶ matches given string in an array
Parameters
const char * const *array- array of strings
size_t n- number of strings in the array or -1 for NULL terminated arrays
const char *str- string to match with
Description
Returns index of str in the array or -EINVAL, just like match_string().
Uses sysfs_streq instead of strcmp for matching.
This routine will look for a string in an array of strings up to the n-th element in the array or until the first NULL element.
Historically the value of -1 for n, was used to search in arrays that are NULL terminated. However, the function does not make a distinction when finishing the search: either n elements have been compared OR the first NULL element was found.
-
void *
memset(void *s, int c, size_t count)¶ Fill a region of memory with the given value
Parameters
void *s- Pointer to the start of the area.
int c- The byte to fill the area with
size_t count- The size of the area.
Description
Do not use memset() to access IO space, use memset_io() instead.
-
void *
memset16(uint16_t *s, uint16_t v, size_t count)¶ Fill a memory area with a uint16_t
Parameters
uint16_t *s- Pointer to the start of the area.
uint16_t v- The value to fill the area with
size_t count- The number of values to store
Description
Differs from memset() in that it fills with a uint16_t instead
of a byte. Remember that count is the number of uint16_ts to
store, not the number of bytes.
-
void *
memset32(uint32_t *s, uint32_t v, size_t count)¶ Fill a memory area with a uint32_t
Parameters
uint32_t *s- Pointer to the start of the area.
uint32_t v- The value to fill the area with
size_t count- The number of values to store
Description
Differs from memset() in that it fills with a uint32_t instead
of a byte. Remember that count is the number of uint32_ts to
store, not the number of bytes.
-
void *
memset64(uint64_t *s, uint64_t v, size_t count)¶ Fill a memory area with a uint64_t
Parameters
uint64_t *s- Pointer to the start of the area.
uint64_t v- The value to fill the area with
size_t count- The number of values to store
Description
Differs from memset() in that it fills with a uint64_t instead
of a byte. Remember that count is the number of uint64_ts to
store, not the number of bytes.
-
void *
memcpy(void *dest, const void *src, size_t count)¶ Copy one area of memory to another
Parameters
void *dest- Where to copy to
const void *src- Where to copy from
size_t count- The size of the area.
Description
You should not use this function to access IO space, use memcpy_toio() or memcpy_fromio() instead.
-
void *
memmove(void *dest, const void *src, size_t count)¶ Copy one area of memory to another
Parameters
void *dest- Where to copy to
const void *src- Where to copy from
size_t count- The size of the area.
Description
Unlike memcpy(), memmove() copes with overlapping areas.
-
__visible int
memcmp(const void *cs, const void *ct, size_t count)¶ Compare two areas of memory
Parameters
const void *cs- One area of memory
const void *ct- Another area of memory
size_t count- The size of the area.
-
int
bcmp(const void *a, const void *b, size_t len)¶ returns 0 if and only if the buffers have identical contents.
Parameters
const void *a- pointer to first buffer.
const void *b- pointer to second buffer.
size_t len- size of buffers.
Description
The sign or magnitude of a non-zero return value has no particular
meaning, and architectures may implement their own more efficient bcmp(). So
while this particular implementation is a simple (tail) call to memcmp, do
not rely on anything but whether the return value is zero or non-zero.
-
void *
memscan(void *addr, int c, size_t size)¶ Find a character in an area of memory.
Parameters
void *addr- The memory area
int c- The byte to search for
size_t size- The size of the area.
Description
returns the address of the first occurrence of c, or 1 byte past the area if c is not found
-
char *
strstr(const char *s1, const char *s2)¶ Find the first substring in a
NULterminated string
Parameters
const char *s1- The string to be searched
const char *s2- The string to search for
-
char *
strnstr(const char *s1, const char *s2, size_t len)¶ Find the first substring in a length-limited string
Parameters
const char *s1- The string to be searched
const char *s2- The string to search for
size_t len- the maximum number of characters to search
-
void *
memchr(const void *s, int c, size_t n)¶ Find a character in an area of memory.
Parameters
const void *s- The memory area
int c- The byte to search for
size_t n- The size of the area.
Description
returns the address of the first occurrence of c, or NULL
if c is not found
-
void *
memchr_inv(const void *start, int c, size_t bytes)¶ Find an unmatching character in an area of memory.
Parameters
const void *start- The memory area
int c- Find a character other than c
size_t bytes- The size of the area.
Description
returns the address of the first character other than c, or NULL
if the whole buffer contains just c.
-
char *
strreplace(char *s, char old, char new)¶ Replace all occurrences of character in string.
Parameters
char *s- The string to operate on.
char old- The character being replaced.
char new- The character old is replaced with.
Description
Returns pointer to the nul byte at the end of s.
-
sysfs_match_string(_a, _s)¶ matches given string in an array
Parameters
_a- array of strings
_s- string to match with
Description
Helper for __sysfs_match_string(). Calculates the size of a automatically.
-
bool
strstarts(const char *str, const char *prefix)¶ does str start with prefix?
Parameters
const char *str- string to examine
const char *prefix- prefix to look for.
-
void
memzero_explicit(void *s, size_t count)¶ Fill a region of memory (e.g. sensitive keying data) with 0s.
Parameters
void *s- Pointer to the start of the area.
size_t count- The size of the area.
Note
usually using memset() is just fine (!), but in cases
where clearing out _local_ data at the end of a scope is
necessary, memzero_explicit() should be used instead in
order to prevent the compiler from optimising away zeroing.
Description
memzero_explicit() doesn’t need an arch-specific version as
it just invokes the one of memset() implicitly.
-
const char *
kbasename(const char *path)¶ return the last part of a pathname.
Parameters
const char *path- path to extract the filename from.
-
void
memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count, int pad)¶ Copy one buffer to another with padding
Parameters
void *dest- Where to copy to
size_t dest_len- The destination buffer size
const void *src- Where to copy from
size_t count- The number of bytes to copy
int pad- Character to use for padding if space is left in destination.
-
size_t
str_has_prefix(const char *str, const char *prefix)¶ Test if a string has a given prefix
Parameters
const char *str- The string to test
const char *prefix- The string to see if str starts with
Description
- A common way to test a prefix of a string is to do:
- strncmp(str, prefix, sizeof(prefix) - 1)
But this can lead to bugs due to typos, or if prefix is a pointer
and not a constant. Instead use str_has_prefix().
Return
- strlen(prefix) if str starts with prefix
- 0 if str does not start with prefix
-
char *
kstrdup(const char *s, gfp_t gfp)¶ allocate space for and copy an existing string
Parameters
const char *s- the string to duplicate
gfp_t gfp- the GFP mask used in the
kmalloc()call when allocating memory
Return
newly allocated copy of s or NULL in case of error
-
const char *
kstrdup_const(const char *s, gfp_t gfp)¶ conditionally duplicate an existing const string
Parameters
const char *s- the string to duplicate
gfp_t gfp- the GFP mask used in the
kmalloc()call when allocating memory
Note
Strings allocated by kstrdup_const should be freed by kfree_const and
must not be passed to krealloc().
Return
source string if it is in .rodata section otherwise fallback to kstrdup.
-
char *
kstrndup(const char *s, size_t max, gfp_t gfp)¶ allocate space for and copy an existing string
Parameters
const char *s- the string to duplicate
size_t max- read at most max chars from s
gfp_t gfp- the GFP mask used in the
kmalloc()call when allocating memory
Note
Use kmemdup_nul() instead if the size is known exactly.
Return
newly allocated copy of s or NULL in case of error
-
void *
kmemdup(const void *src, size_t len, gfp_t gfp)¶ duplicate region of memory
Parameters
const void *src- memory region to duplicate
size_t len- memory region length
gfp_t gfp- GFP mask to use
Return
newly allocated copy of src or NULL in case of error
-
char *
kmemdup_nul(const char *s, size_t len, gfp_t gfp)¶ Create a NUL-terminated string from unterminated data
Parameters
const char *s- The data to stringify
size_t len- The size of the data
gfp_t gfp- the GFP mask used in the
kmalloc()call when allocating memory
Return
newly allocated copy of s with NUL-termination or NULL in
case of error
-
void *
memdup_user(const void __user *src, size_t len)¶ duplicate memory region from user space
Parameters
const void __user *src- source address in user space
size_t len- number of bytes to copy
Return
an ERR_PTR() on failure. Result is physically
contiguous, to be freed by kfree().
-
void *
vmemdup_user(const void __user *src, size_t len)¶ duplicate memory region from user space
Parameters
const void __user *src- source address in user space
size_t len- number of bytes to copy
Return
an ERR_PTR() on failure. Result may be not
physically contiguous. Use kvfree() to free.
-
char *
strndup_user(const char __user *s, long n)¶ duplicate an existing string from user space
Parameters
const char __user *s- The string to duplicate
long n- Maximum number of bytes to copy, including the trailing NUL.
Return
newly allocated copy of s or an ERR_PTR() in case of error
-
void *
memdup_user_nul(const void __user *src, size_t len)¶ duplicate memory region from user space and NUL-terminate
Parameters
const void __user *src- source address in user space
size_t len- number of bytes to copy
Return
an ERR_PTR() on failure.
Basic Kernel Library Functions¶
The Linux kernel provides more basic utility functions.
Bit Operations¶
-
void
set_bit(long nr, volatile unsigned long *addr)¶ Atomically set a bit in memory
Parameters
long nr- the bit to set
volatile unsigned long *addr- the address to start counting from
Description
This is a relaxed atomic operation (no implied memory barriers).
Note that nr may be almost arbitrarily large; this function is not restricted to acting on a single-word quantity.
-
void
clear_bit(long nr, volatile unsigned long *addr)¶ Clears a bit in memory
Parameters
long nr- Bit to clear
volatile unsigned long *addr- Address to start counting from
Description
This is a relaxed atomic operation (no implied memory barriers).
-
void
change_bit(long nr, volatile unsigned long *addr)¶ Toggle a bit in memory
Parameters
long nr- Bit to change
volatile unsigned long *addr- Address to start counting from
Description
This is a relaxed atomic operation (no implied memory barriers).
Note that nr may be almost arbitrarily large; this function is not restricted to acting on a single-word quantity.
-
bool
test_and_set_bit(long nr, volatile unsigned long *addr)¶ Set a bit and return its old value
Parameters
long nr- Bit to set
volatile unsigned long *addr- Address to count from
Description
This is an atomic fully-ordered operation (implied full memory barrier).
-
bool
test_and_clear_bit(long nr, volatile unsigned long *addr)¶ Clear a bit and return its old value
Parameters
long nr- Bit to clear
volatile unsigned long *addr- Address to count from
Description
This is an atomic fully-ordered operation (implied full memory barrier).
-
bool
test_and_change_bit(long nr, volatile unsigned long *addr)¶ Change a bit and return its old value
Parameters
long nr- Bit to change
volatile unsigned long *addr- Address to count from
Description
This is an atomic fully-ordered operation (implied full memory barrier).
-
void
__set_bit(long nr, volatile unsigned long *addr)¶ Set a bit in memory
Parameters
long nr- the bit to set
volatile unsigned long *addr- the address to start counting from
Description
Unlike set_bit(), this function is non-atomic. If it is called on the same
region of memory concurrently, the effect may be that only one operation
succeeds.
-
void
__clear_bit(long nr, volatile unsigned long *addr)¶ Clears a bit in memory
Parameters
long nr- the bit to clear
volatile unsigned long *addr- the address to start counting from
Description
Unlike clear_bit(), this function is non-atomic. If it is called on the same
region of memory concurrently, the effect may be that only one operation
succeeds.
-
void
__change_bit(long nr, volatile unsigned long *addr)¶ Toggle a bit in memory
Parameters
long nr- the bit to change
volatile unsigned long *addr- the address to start counting from
Description
Unlike change_bit(), this function is non-atomic. If it is called on the same
region of memory concurrently, the effect may be that only one operation
succeeds.
-
bool
__test_and_set_bit(long nr, volatile unsigned long *addr)¶ Set a bit and return its old value
Parameters
long nr- Bit to set
volatile unsigned long *addr- Address to count from
Description
This operation is non-atomic. If two instances of this operation race, one can appear to succeed but actually fail.
-
bool
__test_and_clear_bit(long nr, volatile unsigned long *addr)¶ Clear a bit and return its old value
Parameters
long nr- Bit to clear
volatile unsigned long *addr- Address to count from
Description
This operation is non-atomic. If two instances of this operation race, one can appear to succeed but actually fail.
-
bool
__test_and_change_bit(long nr, volatile unsigned long *addr)¶ Change a bit and return its old value
Parameters
long nr- Bit to change
volatile unsigned long *addr- Address to count from
Description
This operation is non-atomic. If two instances of this operation race, one can appear to succeed but actually fail.
-
bool
test_bit(long nr, const volatile unsigned long *addr)¶ Determine whether a bit is set
Parameters
long nr- bit number to test
const volatile unsigned long *addr- Address to start counting from
-
void
clear_bit_unlock(long nr, volatile unsigned long *addr)¶ Clear a bit in memory, for unlock
Parameters
long nr- the bit to set
volatile unsigned long *addr- the address to start counting from
Description
This operation is atomic and provides release barrier semantics.
-
void
__clear_bit_unlock(long nr, volatile unsigned long *addr)¶ Clears a bit in memory
Parameters
long nr- Bit to clear
volatile unsigned long *addr- Address to start counting from
Description
This is a non-atomic operation but implies a release barrier before the memory operation. It can be used for an unlock if no other CPUs can concurrently modify other bits in the word.
-
bool
test_and_set_bit_lock(long nr, volatile unsigned long *addr)¶ Set a bit and return its old value, for lock
Parameters
long nr- Bit to set
volatile unsigned long *addr- Address to count from
Description
This operation is atomic and provides acquire barrier semantics if the returned value is 0. It can be used to implement bit locks.
-
bool
clear_bit_unlock_is_negative_byte(long nr, volatile unsigned long *addr)¶ Clear a bit in memory and test if bottom byte is negative, for unlock.
Parameters
long nr- the bit to clear
volatile unsigned long *addr- the address to start counting from
Description
This operation is atomic and provides release barrier semantics.
This is a bit of a one-trick-pony for the filemap code, which clears PG_locked and tests PG_waiters,
Bitmap Operations¶
bitmaps provide an array of bits, implemented using an array of unsigned longs. The number of valid bits in a given bitmap does _not_ need to be an exact multiple of BITS_PER_LONG.
The possible unused bits in the last, partially used word of a bitmap are ‘don’t care’. The implementation makes no particular effort to keep them zero. It ensures that their value will not affect the results of any operation. The bitmap operations that return Boolean (bitmap_empty, for example) or scalar (bitmap_weight, for example) results carefully filter out these unused bits from impacting their results.
The byte ordering of bitmaps is more natural on little endian architectures. See the big-endian headers include/asm-ppc64/bitops.h and include/asm-s390/bitops.h for the best explanations of this ordering.
The DECLARE_BITMAP(name,bits) macro, in linux/types.h, can be used to declare an array named ‘name’ of just enough unsigned longs to contain all bit positions from 0 to ‘bits’ - 1.
The available bitmap operations and their rough meaning in the case that the bitmap is a single unsigned long are thus:
The generated code is more efficient when nbits is known at compile-time and at most BITS_PER_LONG.
bitmap_zero(dst, nbits) *dst = 0UL
bitmap_fill(dst, nbits) *dst = ~0UL
bitmap_copy(dst, src, nbits) *dst = *src
bitmap_and(dst, src1, src2, nbits) *dst = *src1 & *src2
bitmap_or(dst, src1, src2, nbits) *dst = *src1 | *src2
bitmap_xor(dst, src1, src2, nbits) *dst = *src1 ^ *src2
bitmap_andnot(dst, src1, src2, nbits) *dst = *src1 & ~(*src2)
bitmap_complement(dst, src, nbits) *dst = ~(*src)
bitmap_equal(src1, src2, nbits) Are *src1 and *src2 equal?
bitmap_intersects(src1, src2, nbits) Do *src1 and *src2 overlap?
bitmap_subset(src1, src2, nbits) Is *src1 a subset of *src2?
bitmap_empty(src, nbits) Are all bits zero in *src?
bitmap_full(src, nbits) Are all bits set in *src?
bitmap_weight(src, nbits) Hamming Weight: number set bits
bitmap_set(dst, pos, nbits) Set specified bit area
bitmap_clear(dst, pos, nbits) Clear specified bit area
bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free area
bitmap_find_next_zero_area_off(buf, len, pos, n, mask, mask_off) as above
bitmap_next_clear_region(map, :c:type:`start`, :c:type:`end`, nbits) Find next clear region
bitmap_next_set_region(map, :c:type:`start`, :c:type:`end`, nbits) Find next set region
bitmap_for_each_clear_region(map, rs, re, start, end)
Iterate over all clear regions
bitmap_for_each_set_region(map, rs, re, start, end)
Iterate over all set regions
bitmap_shift_right(dst, src, n, nbits) *dst = *src >> n
bitmap_shift_left(dst, src, n, nbits) *dst = *src << n
bitmap_cut(dst, src, first, n, nbits) Cut n bits from first, copy rest
bitmap_replace(dst, old, new, mask, nbits) *dst = (*old & ~(*mask)) | (*new & *mask)
bitmap_remap(dst, src, old, new, nbits) *dst = map(old, new)(src)
bitmap_bitremap(oldbit, old, new, nbits) newbit = map(old, new)(oldbit)
bitmap_onto(dst, orig, relmap, nbits) *dst = orig relative to relmap
bitmap_fold(dst, orig, sz, nbits) dst bits = orig bits mod sz
bitmap_parse(buf, buflen, dst, nbits) Parse bitmap dst from kernel buf
bitmap_parse_user(ubuf, ulen, dst, nbits) Parse bitmap dst from user buf
bitmap_parselist(buf, dst, nbits) Parse bitmap dst from kernel buf
bitmap_parselist_user(buf, dst, nbits) Parse bitmap dst from user buf
bitmap_find_free_region(bitmap, bits, order) Find and allocate bit region
bitmap_release_region(bitmap, pos, order) Free specified bit region
bitmap_allocate_region(bitmap, pos, order) Allocate specified bit region
bitmap_from_arr32(dst, buf, nbits) Copy nbits from u32[] buf to dst
bitmap_to_arr32(buf, src, nbits) Copy nbits from buf to u32[] dst
bitmap_get_value8(map, start) Get 8bit value from map at start
bitmap_set_value8(map, value, start) Set 8bit value to map at start
Note, bitmap_zero() and bitmap_fill() operate over the region of unsigned longs, that is, bits behind bitmap till the unsigned long boundary will be zeroed or filled as well. Consider to use bitmap_clear() or bitmap_set() to make explicit zeroing or filling respectively.
Also the following operations in asm/bitops.h apply to bitmaps.:
set_bit(bit, addr) *addr |= bit
clear_bit(bit, addr) *addr &= ~bit
change_bit(bit, addr) *addr ^= bit
test_bit(bit, addr) Is bit set in *addr?
test_and_set_bit(bit, addr) Set bit and return old value
test_and_clear_bit(bit, addr) Clear bit and return old value
test_and_change_bit(bit, addr) Change bit and return old value
find_first_zero_bit(addr, nbits) Position first zero bit in *addr
find_first_bit(addr, nbits) Position first set bit in *addr
find_next_zero_bit(addr, nbits, bit)
Position next zero bit in *addr >= bit
find_next_bit(addr, nbits, bit) Position next set bit in *addr >= bit
find_next_and_bit(addr1, addr2, nbits, bit)
Same as find_next_bit, but in
(*addr1 & *addr2)
-
void
__bitmap_shift_right(unsigned long *dst, const unsigned long *src, unsigned shift, unsigned nbits)¶ logical right shift of the bits in a bitmap
Parameters
unsigned long *dst- destination bitmap
const unsigned long *src- source bitmap
unsigned shift- shift by this many bits
unsigned nbits- bitmap size, in bits
Description
Shifting right (dividing) means moving bits in the MS -> LS bit direction. Zeros are fed into the vacated MS positions and the LS bits shifted off the bottom are lost.
-
void
__bitmap_shift_left(unsigned long *dst, const unsigned long *src, unsigned int shift, unsigned int nbits)¶ logical left shift of the bits in a bitmap
Parameters
unsigned long *dst- destination bitmap
const unsigned long *src- source bitmap
unsigned int shift- shift by this many bits
unsigned int nbits- bitmap size, in bits
Description
Shifting left (multiplying) means moving bits in the LS -> MS direction. Zeros are fed into the vacated LS bit positions and those MS bits shifted off the top are lost.
-
void
bitmap_cut(unsigned long *dst, const unsigned long *src, unsigned int first, unsigned int cut, unsigned int nbits)¶ remove bit region from bitmap and right shift remaining bits
Parameters
unsigned long *dst- destination bitmap, might overlap with src
const unsigned long *src- source bitmap
unsigned int first- start bit of region to be removed
unsigned int cut- number of bits to remove
unsigned int nbits- bitmap size, in bits
Description
Set the n-th bit of dst iff the n-th bit of src is set and n is less than first, or the m-th bit of src is set for any m such that first <= n < nbits, and m = n + cut.
In pictures, example for a big-endian 32-bit architecture:
The src bitmap is:
31 63
| |
10000000 11000001 11110010 00010101 10000000 11000001 01110010 00010101
| | | |
16 14 0 32
if cut is 3, and first is 14, bits 14-16 in src are cut and dst is:
31 63
| |
10110000 00011000 00110010 00010101 00010000 00011000 00101110 01000010
| | |
14 (bit 17 0 32
from @src)
Note that dst and src might overlap partially or entirely.
This is implemented in the obvious way, with a shift and carry step for each moved bit. Optimisation is left as an exercise for the compiler.
-
unsigned long
bitmap_find_next_zero_area_off(unsigned long *map, unsigned long size, unsigned long start, unsigned int nr, unsigned long align_mask, unsigned long align_offset)¶ find a contiguous aligned zero area
Parameters
unsigned long *map- The address to base the search on
unsigned long size- The bitmap size in bits
unsigned long start- The bitnumber to start searching at
unsigned int nr- The number of zeroed bits we’re looking for
unsigned long align_mask- Alignment mask for zero area
unsigned long align_offset- Alignment offset for zero area.
Description
The align_mask should be one less than a power of 2; the effect is that the bit offset of all zero areas this function finds plus align_offset is multiple of that power of 2.
-
int
bitmap_parse_user(const char __user *ubuf, unsigned int ulen, unsigned long *maskp, int nmaskbits)¶ convert an ASCII hex string in a user buffer into a bitmap
Parameters
const char __user *ubuf- pointer to user buffer containing string.
unsigned int ulen- buffer size in bytes. If string is smaller than this then it must be terminated with a 0.
unsigned long *maskp- pointer to bitmap array that will contain result.
int nmaskbits- size of bitmap, in bits.
-
int
bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp, int nmaskbits)¶ convert bitmap to list or hex format ASCII string
Parameters
bool list- indicates whether the bitmap must be list
char *buf- page aligned buffer into which string is placed
const unsigned long *maskp- pointer to bitmap to convert
int nmaskbits- size of bitmap, in bits
Description
Output format is a comma-separated list of decimal numbers and ranges if list is specified or hex digits grouped into comma-separated sets of 8 digits/set. Returns the number of characters written to buf.
It is assumed that buf is a pointer into a PAGE_SIZE, page-aligned
area and that sufficient storage remains at buf to accommodate the
bitmap_print_to_pagebuf() output. Returns the number of characters
actually printed to buf, excluding terminating ‘0’.
-
int
bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)¶ convert list format ASCII string to bitmap
Parameters
const char *buf- read user string from this buffer; must be terminated with a 0 or n.
unsigned long *maskp- write resulting mask here
int nmaskbits- number of bits in mask to be written
Description
Input format is a comma-separated list of decimal numbers and ranges. Consecutively set bits are shown as two hyphen-separated decimal numbers, the smallest and largest bit numbers set in the range. Optionally each range can be postfixed to denote that only parts of it should be set. The range will divided to groups of specific size. From each group will be used only defined amount of bits. Syntax: range:used_size/group_size
Example
0-1023:2/256 ==> 0,1,256,257,512,513,768,769
Return
0 on success, -errno on invalid input strings. Error values:
-EINVAL: wrong region format-EINVAL: invalid character in string-ERANGE: bit number specified too large for mask-EOVERFLOW: integer overflow in the input parameters
-
int
bitmap_parselist_user(const char __user *ubuf, unsigned int ulen, unsigned long *maskp, int nmaskbits)¶
Parameters
const char __user *ubuf- pointer to user buffer containing string.
unsigned int ulen- buffer size in bytes. If string is smaller than this then it must be terminated with a 0.
unsigned long *maskp- pointer to bitmap array that will contain result.
int nmaskbits- size of bitmap, in bits.
Description
Wrapper for bitmap_parselist(), providing it with user buffer.
-
int
bitmap_parse(const char *start, unsigned int buflen, unsigned long *maskp, int nmaskbits)¶ convert an ASCII hex string into a bitmap.
Parameters
const char *start- pointer to buffer containing string.
unsigned int buflen- buffer size in bytes. If string is smaller than this then it must be terminated with a 0 or n. In that case, UINT_MAX may be provided instead of string length.
unsigned long *maskp- pointer to bitmap array that will contain result.
int nmaskbits- size of bitmap, in bits.
Description
Commas group hex digits into chunks. Each chunk defines exactly 32
bits of the resultant bitmask. No chunk may specify a value larger
than 32 bits (-EOVERFLOW), and if a chunk specifies a smaller value
then leading 0-bits are prepended. -EINVAL is returned for illegal
characters. Grouping such as “1,,5”, “,44”, “,” or “” is allowed.
Leading, embedded and trailing whitespace accepted.
-
int
bitmap_find_free_region(unsigned long *bitmap, unsigned int bits, int order)¶ find a contiguous aligned mem region
Parameters
unsigned long *bitmap- array of unsigned longs corresponding to the bitmap
unsigned int bits- number of bits in the bitmap
int order- region size (log base 2 of number of bits) to find
Description
Find a region of free (zero) bits in a bitmap of bits bits and allocate them (set them to one). Only consider regions of length a power (order) of two, aligned to that power of two, which makes the search algorithm much faster.
Return the bit offset in bitmap of the allocated region, or -errno on failure.
-
void
bitmap_release_region(unsigned long *bitmap, unsigned int pos, int order)¶ release allocated bitmap region
Parameters
unsigned long *bitmap- array of unsigned longs corresponding to the bitmap
unsigned int pos- beginning of bit region to release
int order- region size (log base 2 of number of bits) to release
Description
This is the complement to __bitmap_find_free_region() and releases the found region (by clearing it in the bitmap).
No return value.
-
int
bitmap_allocate_region(unsigned long *bitmap, unsigned int pos, int order)¶ allocate bitmap region
Parameters
unsigned long *bitmap- array of unsigned longs corresponding to the bitmap
unsigned int pos- beginning of bit region to allocate
int order- region size (log base 2 of number of bits) to allocate
Description
Allocate (set bits in) a specified region of a bitmap.
Return 0 on success, or -EBUSY if specified region wasn’t
free (not all bits were zero).
-
void
bitmap_copy_le(unsigned long *dst, const unsigned long *src, unsigned int nbits)¶ copy a bitmap, putting the bits into little-endian order.
Parameters
unsigned long *dst- destination buffer
const unsigned long *src- bitmap to copy
unsigned int nbits- number of bits in the bitmap
Description
Require nbits % BITS_PER_LONG == 0.
-
void
bitmap_from_arr32(unsigned long *bitmap, const u32 *buf, unsigned int nbits)¶ copy the contents of u32 array of bits to bitmap
Parameters
unsigned long *bitmap- array of unsigned longs, the destination bitmap
const u32 *buf- array of u32 (in host byte order), the source bitmap
unsigned int nbits- number of bits in bitmap
-
void
bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits)¶ copy the contents of bitmap to a u32 array of bits
Parameters
u32 *buf- array of u32 (in host byte order), the dest bitmap
const unsigned long *bitmap- array of unsigned longs, the source bitmap
unsigned int nbits- number of bits in bitmap
-
int
bitmap_pos_to_ord(const unsigned long *buf, unsigned int pos, unsigned int nbits)¶ find ordinal of set bit at given position in bitmap
Parameters
const unsigned long *buf- pointer to a bitmap
unsigned int pos- a bit position in buf (0 <= pos < nbits)
unsigned int nbits- number of valid bit positions in buf
Description
Map the bit at position pos in buf (of length nbits) to the ordinal of which set bit it is. If it is not set or if pos is not a valid bit position, map to -1.
If for example, just bits 4 through 7 are set in buf, then pos values 4 through 7 will get mapped to 0 through 3, respectively, and other pos values will get mapped to -1. When pos value 7 gets mapped to (returns) ord value 3 in this example, that means that bit 7 is the 3rd (starting with 0th) set bit in buf.
The bit positions 0 through bits are valid positions in buf.
-
unsigned int
bitmap_ord_to_pos(const unsigned long *buf, unsigned int ord, unsigned int nbits)¶ find position of n-th set bit in bitmap
Parameters
const unsigned long *buf- pointer to bitmap
unsigned int ord- ordinal bit position (n-th set bit, n >= 0)
unsigned int nbits- number of valid bit positions in buf
Description
Map the ordinal offset of bit ord in buf to its position in buf. Value of ord should be in range 0 <= ord < weight(buf). If ord >= weight(buf), returns nbits.
If for example, just bits 4 through 7 are set in buf, then ord values 0 through 3 will get mapped to 4 through 7, respectively, and all other ord values returns nbits. When ord value 3 gets mapped to (returns) pos value 7 in this example, that means that the 3rd set bit (starting with 0th) is at position 7 in buf.
The bit positions 0 through nbits-1 are valid positions in buf.
-
void
bitmap_remap(unsigned long *dst, const unsigned long *src, const unsigned long *old, const unsigned long *new, unsigned int nbits)¶ Apply map defined by a pair of bitmaps to another bitmap
Parameters
unsigned long *dst- remapped result
const unsigned long *src- subset to be remapped
const unsigned long *old- defines domain of map
const unsigned long *new- defines range of map
unsigned int nbits- number of bits in each of these bitmaps
Description
Let old and new define a mapping of bit positions, such that whatever position is held by the n-th set bit in old is mapped to the n-th set bit in new. In the more general case, allowing for the possibility that the weight ‘w’ of new is less than the weight of old, map the position of the n-th set bit in old to the position of the m-th set bit in new, where m == n % w.
If either of the old and new bitmaps are empty, or if src and dst point to the same location, then this routine copies src to dst.
The positions of unset bits in old are mapped to themselves (the identify map).
Apply the above specified mapping to src, placing the result in dst, clearing any bits previously set in dst.
For example, lets say that old has bits 4 through 7 set, and new has bits 12 through 15 set. This defines the mapping of bit position 4 to 12, 5 to 13, 6 to 14 and 7 to 15, and of all other bit positions unchanged. So if say src comes into this routine with bits 1, 5 and 7 set, then dst should leave with bits 1, 13 and 15 set.
-
int
bitmap_bitremap(int oldbit, const unsigned long *old, const unsigned long *new, int bits)¶ Apply map defined by a pair of bitmaps to a single bit
Parameters
int oldbit- bit position to be mapped
const unsigned long *old- defines domain of map
const unsigned long *new- defines range of map
int bits- number of bits in each of these bitmaps
Description
Let old and new define a mapping of bit positions, such that whatever position is held by the n-th set bit in old is mapped to the n-th set bit in new. In the more general case, allowing for the possibility that the weight ‘w’ of new is less than the weight of old, map the position of the n-th set bit in old to the position of the m-th set bit in new, where m == n % w.
The positions of unset bits in old are mapped to themselves (the identify map).
Apply the above specified mapping to bit position oldbit, returning the new bit position.
For example, lets say that old has bits 4 through 7 set, and new has bits 12 through 15 set. This defines the mapping of bit position 4 to 12, 5 to 13, 6 to 14 and 7 to 15, and of all other bit positions unchanged. So if say oldbit is 5, then this routine returns 13.
-
void
bitmap_onto(unsigned long *dst, const unsigned long *orig, const unsigned long *relmap, unsigned int bits)¶ translate one bitmap relative to another
Parameters
unsigned long *dst- resulting translated bitmap
const unsigned long *orig- original untranslated bitmap
const unsigned long *relmap- bitmap relative to which translated
unsigned int bits- number of bits in each of these bitmaps
Description
Set the n-th bit of dst iff there exists some m such that the n-th bit of relmap is set, the m-th bit of orig is set, and the n-th bit of relmap is also the m-th _set_ bit of relmap. (If you understood the previous sentence the first time your read it, you’re overqualified for your current job.)
In other words, orig is mapped onto (surjectively) dst, using the map { <n, m> | the n-th bit of relmap is the m-th set bit of relmap }.
Any set bits in orig above bit number W, where W is the
weight of (number of set bits in) relmap are mapped nowhere.
In particular, if for all bits m set in orig, m >= W, then
dst will end up empty. In situations where the possibility
of such an empty result is not desired, one way to avoid it is
to use the bitmap_fold() operator, below, to first fold the
orig bitmap over itself so that all its set bits x are in the
range 0 <= x < W. The bitmap_fold() operator does this by
setting the bit (m % W) in dst, for each bit (m) set in orig.
- Example [1] for bitmap_onto():
Let’s say relmap has bits 30-39 set, and orig has bits 1, 3, 5, 7, 9 and 11 set. Then on return from this routine, dst will have bits 31, 33, 35, 37 and 39 set.
When bit 0 is set in orig, it means turn on the bit in dst corresponding to whatever is the first bit (if any) that is turned on in relmap. Since bit 0 was off in the above example, we leave off that bit (bit 30) in dst.
When bit 1 is set in orig (as in the above example), it means turn on the bit in dst corresponding to whatever is the second bit that is turned on in relmap. The second bit in relmap that was turned on in the above example was bit 31, so we turned on bit 31 in dst.
Similarly, we turned on bits 33, 35, 37 and 39 in dst, because they were the 4th, 6th, 8th and 10th set bits set in relmap, and the 4th, 6th, 8th and 10th bits of orig (i.e. bits 3, 5, 7 and 9) were also set.
When bit 11 is set in orig, it means turn on the bit in dst corresponding to whatever is the twelfth bit that is turned on in relmap. In the above example, there were only ten bits turned on in relmap (30..39), so that bit 11 was set in orig had no affect on dst.
- Example [2] for bitmap_fold() + bitmap_onto():
Let’s say relmap has these ten bits set:
40 41 42 43 45 48 53 61 74 95
(for the curious, that’s 40 plus the first ten terms of the Fibonacci sequence.)
Further lets say we use the following code, invoking
bitmap_fold()then bitmap_onto, as suggested above to avoid the possibility of an empty dst result:unsigned long *tmp; // a temporary bitmap's bits bitmap_fold(tmp, orig, bitmap_weight(relmap, bits), bits); bitmap_onto(dst, tmp, relmap, bits);
Then this table shows what various values of dst would be, for various orig’s. I list the zero-based positions of each set bit. The tmp column shows the intermediate result, as computed by using
bitmap_fold()to fold the orig bitmap modulo ten (the weight of relmap):
| [1] | (1, 2) For these marked lines, if we hadn’t first done bitmap_fold()
into tmp, then the dst result would have been empty. |
If either of orig or relmap is empty (no set bits), then dst will be returned empty.
If (as explained above) the only set bits in orig are in positions m where m >= W, (where W is the weight of relmap) then dst will once again be returned empty.
All bits in dst not set by the above rule are cleared.
-
void
bitmap_fold(unsigned long *dst, const unsigned long *orig, unsigned int sz, unsigned int nbits)¶ fold larger bitmap into smaller, modulo specified size
Parameters
unsigned long *dst- resulting smaller bitmap
const unsigned long *orig- original larger bitmap
unsigned int sz- specified size
unsigned int nbits- number of bits in each of these bitmaps
Description
For each bit oldbit in orig, set bit oldbit mod sz in dst.
Clear all other bits in dst. See further the comment and
Example [2] for bitmap_onto() for why and how to use this.
-
unsigned long
bitmap_find_next_zero_area(unsigned long *map, unsigned long size, unsigned long start, unsigned int nr, unsigned long align_mask)¶ find a contiguous aligned zero area
Parameters
unsigned long *map- The address to base the search on
unsigned long size- The bitmap size in bits
unsigned long start- The bitnumber to start searching at
unsigned int nr- The number of zeroed bits we’re looking for
unsigned long align_mask- Alignment mask for zero area
Description
The align_mask should be one less than a power of 2; the effect is that the bit offset of all zero areas this function finds is multiples of that power of 2. A align_mask of 0 means no alignment is required.
-
bool
bitmap_or_equal(const unsigned long *src1, const unsigned long *src2, const unsigned long *src3, unsigned int nbits)¶ Check whether the or of two bitmaps is equal to a third
Parameters
const unsigned long *src1- Pointer to bitmap 1
const unsigned long *src2- Pointer to bitmap 2 will be or’ed with bitmap 1
const unsigned long *src3- Pointer to bitmap 3. Compare to the result of *src1 | *src2
unsigned int nbits- number of bits in each of these bitmaps
Return
True if (*src1 | *src2) == *src3, false otherwise
-
BITMAP_FROM_U64(n)¶ Represent u64 value in the format suitable for bitmap.
Parameters
n- u64 value
Description
Linux bitmaps are internally arrays of unsigned longs, i.e. 32-bit integers in 32-bit environment, and 64-bit integers in 64-bit one.
There are four combinations of endianness and length of the word in linux ABIs: LE64, BE64, LE32 and BE32.
On 64-bit kernels 64-bit LE and BE numbers are naturally ordered in bitmaps and therefore don’t require any special handling.
On 32-bit kernels 32-bit LE ABI orders lo word of 64-bit number in memory prior to hi, and 32-bit BE orders hi word prior to lo. The bitmap on the other hand is represented as an array of 32-bit words and the position of bit N may therefore be calculated as: word #(N/32) and bit #(N``32``) in that word. For example, bit #42 is located at 10th position of 2nd word. It matches 32-bit LE ABI, and we can simply let the compiler store 64-bit values in memory as it usually does. But for BE we need to swap hi and lo words manually.
With all that, the macro BITMAP_FROM_U64() does explicit reordering of hi and
lo parts of u64. For LE32 it does nothing, and for BE environment it swaps
hi and lo words, as is expected by bitmap.
-
void
bitmap_from_u64(unsigned long *dst, u64 mask)¶ Check and swap words within u64.
Parameters
unsigned long *dst- destination bitmap
u64 mask- source bitmap
Description
In 32-bit Big Endian kernel, when using (u32 *)(:c:type:`val`)[*]
to read u64 mask, we will get the wrong word.
That is (u32 *)(:c:type:`val`)[0] gets the upper 32 bits,
but we expect the lower 32-bits of u64.
-
unsigned long
bitmap_get_value8(const unsigned long *map, unsigned long start)¶ get an 8-bit value within a memory region
Parameters
const unsigned long *map- address to the bitmap memory region
unsigned long start- bit offset of the 8-bit value; must be a multiple of 8
Description
Returns the 8-bit value located at the start bit offset within the src memory region.
-
void
bitmap_set_value8(unsigned long *map, unsigned long value, unsigned long start)¶ set an 8-bit value within a memory region
Parameters
unsigned long *map- address to the bitmap memory region
unsigned long value- the 8-bit value; values wider than 8 bits may clobber bitmap
unsigned long start- bit offset of the 8-bit value; must be a multiple of 8
Command-line Parsing¶
-
int
get_option(char **str, int *pint)¶ Parse integer from an option string
Parameters
char **str- option string
int *pint(optional output) integer value parsed from str
Read an int from an option string; if available accept a subsequent comma as well.
When pint is NULL the function can be used as a validator of the current option in the string.
Return values: 0 - no int in string 1 - int found, no subsequent comma 2 - int found including a subsequent comma 3 - hyphen found to denote a range
Leading hyphen without integer is no integer case, but we consume it for the sake of simplification.
-
char *
get_options(const char *str, int nints, int *ints)¶ Parse a string into a list of integers
Parameters
const char *str- String to be parsed
int nints- size of integer array
int *intsinteger array
This function parses a string containing a comma-separated list of integers, a hyphen-separated range of _positive_ integers, or a combination of both. The parse halts when the array is full, or when no more numbers can be retrieved from the string.
Return value is the character in the string which caused the parse to end (typically a null terminator, if str is completely parseable).
-
unsigned long long
memparse(const char *ptr, char **retptr)¶ parse a string with mem suffixes into a number
Parameters
const char *ptr- Where parse begins
char **retptr(output) Optional pointer to next char after parse completes
Parses a string into a number. The number stored at ptr is potentially suffixed with K, M, G, T, P, E.
Sorting¶
-
void
sort_r(void *base, size_t num, size_t size, cmp_r_func_t cmp_func, swap_func_t swap_func, const void *priv)¶ sort an array of elements
Parameters
void *base- pointer to data to sort
size_t num- number of elements
size_t size- size of each element
cmp_r_func_t cmp_func- pointer to comparison function
swap_func_t swap_func- pointer to swap function or NULL
const void *priv- third argument passed to comparison function
Description
This function does a heapsort on the given array. You may provide a swap_func function if you need to do something more than a memory copy (e.g. fix up pointers or auxiliary data), but the built-in swap avoids a slow retpoline and so is significantly faster.
Sorting time is O(n log n) both on average and worst-case. While quicksort is slightly faster on average, it suffers from exploitable O(n*n) worst-case behavior and extra memory requirements that make it less suitable for kernel use.
-
void
list_sort(void *priv, struct list_head *head, int (*cmp)(void *priv, struct list_head *a, struct list_head *b))¶ sort a list
Parameters
void *priv- private data, opaque to
list_sort(), passed to cmp struct list_head *head- the list to sort
int (*cmp)(void *priv, struct list_head *a, struct list_head *b)- the elements comparison function
Description
The comparison funtion cmp must return > 0 if a should sort after b (“a > b” if you want an ascending sort), and <= 0 if a should sort before b or their original order should be preserved. It is always called with the element that came first in the input in a, and list_sort is a stable sort, so it is not necessary to distinguish the a < b and a == b cases.
This is compatible with two styles of cmp function: - The traditional style which returns <0 / =0 / >0, or - Returning a boolean 0/1. The latter offers a chance to save a few cycles in the comparison (which is used by e.g. plug_ctx_cmp() in block/blk-mq.c).
A good way to write a multi-word comparison is:
if (a->high != b->high)
return a->high > b->high;
if (a->middle != b->middle)
return a->middle > b->middle;
return a->low > b->low;
This mergesort is as eager as possible while always performing at least 2:1 balanced merges. Given two pending sublists of size 2^k, they are merged to a size-2^(k+1) list as soon as we have 2^k following elements.
Thus, it will avoid cache thrashing as long as 3*2^k elements can fit into the cache. Not quite as good as a fully-eager bottom-up mergesort, but it does use 0.2*n fewer comparisons, so is faster in the common case that everything fits into L1.
The merging is controlled by “count”, the number of elements in the pending lists. This is beautiully simple code, but rather subtle.
Each time we increment “count”, we set one bit (bit k) and clear bits k-1 .. 0. Each time this happens (except the very first time for each bit, when count increments to 2^k), we merge two lists of size 2^k into one list of size 2^(k+1).
This merge happens exactly when the count reaches an odd multiple of 2^k, which is when we have 2^k elements pending in smaller lists, so it’s safe to merge away two lists of size 2^k.
After this happens twice, we have created two lists of size 2^(k+1), which will be merged into a list of size 2^(k+2) before we create a third list of size 2^(k+1), so there are never more than two pending.
The number of pending lists of size 2^k is determined by the state of bit k of “count” plus two extra pieces of information:
- The state of bit k-1 (when k == 0, consider bit -1 always set), and
- Whether the higher-order bits are zero or non-zero (i.e. is count >= 2^(k+1)).
There are six states we distinguish. “x” represents some arbitrary bits, and “y” represents some arbitrary non-zero bits: 0: 00x: 0 pending of size 2^k; x pending of sizes < 2^k 1: 01x: 0 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k 2: x10x: 0 pending of size 2^k; 2^k + x pending of sizes < 2^k 3: x11x: 1 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k 4: y00x: 1 pending of size 2^k; 2^k + x pending of sizes < 2^k 5: y01x: 2 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k (merge and loop back to state 2)
We gain lists of size 2^k in the 2->3 and 4->5 transitions (because bit k-1 is set while the more significant bits are non-zero) and merge them away in the 5->2 transition. Note in particular that just before the 5->2 transition, all lower-order bits are 11 (state 3), so there is one list of each smaller size.
When we reach the end of the input, we merge all the pending lists, from smallest to largest. If you work through cases 2 to 5 above, you can see that the number of elements we merge with a list of size 2^k varies from 2^(k-1) (cases 3 and 5 when x == 0) to 2^(k+1) - 1 (second merge of case 5 when x == 2^(k-1) - 1).
Text Searching¶
INTRODUCTION
The textsearch infrastructure provides text searching facilities for both linear and non-linear data. Individual search algorithms are implemented in modules and chosen by the user.
ARCHITECTURE
User
+----------------+
| finish()|<--------------(6)-----------------+
|get_next_block()|<--------------(5)---------------+ |
| | Algorithm | |
| | +------------------------------+
| | | init() find() destroy() |
| | +------------------------------+
| | Core API ^ ^ ^
| | +---------------+ (2) (4) (8)
| (1)|----->| prepare() |---+ | |
| (3)|----->| find()/next() |-----------+ |
| (7)|----->| destroy() |----------------------+
+----------------+ +---------------+
(1) User configures a search by calling textsearch_prepare() specifying
the search parameters such as the pattern and algorithm name.
(2) Core requests the algorithm to allocate and initialize a search
configuration according to the specified parameters.
(3) User starts the search(es) by calling textsearch_find() or
textsearch_next() to fetch subsequent occurrences. A state variable
is provided to the algorithm to store persistent variables.
(4) Core eventually resets the search offset and forwards the find()
request to the algorithm.
(5) Algorithm calls get_next_block() provided by the user continuously
to fetch the data to be searched in block by block.
(6) Algorithm invokes finish() after the last call to get_next_block
to clean up any leftovers from get_next_block. (Optional)
(7) User destroys the configuration by calling textsearch_destroy().
(8) Core notifies the algorithm to destroy algorithm specific
allocations. (Optional)
USAGE
Before a search can be performed, a configuration must be created by calling
textsearch_prepare()specifying the searching algorithm, the pattern to look for and flags. As a flag, you can set TS_IGNORECASE to perform case insensitive matching. But it might slow down performance of algorithm, so you should use it at own your risk. The returned configuration may then be used for an arbitrary amount of times and even in parallel as long as a separate struct ts_state variable is provided to every instance.The actual search is performed by either calling
textsearch_find_continuous()for linear data or by providing an own get_next_block() implementation and callingtextsearch_find(). Both functions return the position of the first occurrence of the pattern or UINT_MAX if no match was found. Subsequent occurrences can be found by callingtextsearch_next()regardless of the linearity of the data.Once you’re done using a configuration it must be given back via textsearch_destroy.
EXAMPLE:
int pos;
struct ts_config *conf;
struct ts_state state;
const char *pattern = "chicken";
const char *example = "We dance the funky chicken";
conf = textsearch_prepare("kmp", pattern, strlen(pattern),
GFP_KERNEL, TS_AUTOLOAD);
if (IS_ERR(conf)) {
err = PTR_ERR(conf);
goto errout;
}
pos = textsearch_find_continuous(conf, &state, example, strlen(example));
if (pos != UINT_MAX)
panic("Oh my god, dancing chickens at %d\n", pos);
textsearch_destroy(conf);
-
int
textsearch_register(struct ts_ops *ops)¶ register a textsearch module
Parameters
struct ts_ops *ops- operations lookup table
Description
This function must be called by textsearch modules to announce
their presence. The specified &**ops** must have name set to a
unique identifier and the callbacks find(), init(), get_pattern(),
and get_pattern_len() must be implemented.
Returns 0 or -EEXISTS if another module has already registered with same name.
-
int
textsearch_unregister(struct ts_ops *ops)¶ unregister a textsearch module
Parameters
struct ts_ops *ops- operations lookup table
Description
This function must be called by textsearch modules to announce
their disappearance for examples when the module gets unloaded.
The ops parameter must be the same as the one during the
registration.
Returns 0 on success or -ENOENT if no matching textsearch registration was found.
-
unsigned int
textsearch_find_continuous(struct ts_config *conf, struct ts_state *state, const void *data, unsigned int len)¶ search a pattern in continuous/linear data
Parameters
struct ts_config *conf- search configuration
struct ts_state *state- search state
const void *data- data to search in
unsigned int len- length of data
Description
A simplified version of textsearch_find() for continuous/linear data.
Call textsearch_next() to retrieve subsequent matches.
Returns the position of first occurrence of the pattern or
UINT_MAX if no occurrence was found.
-
struct ts_config *
textsearch_prepare(const char *algo, const void *pattern, unsigned int len, gfp_t gfp_mask, int flags)¶ Prepare a search
Parameters
const char *algo- name of search algorithm
const void *pattern- pattern data
unsigned int len- length of pattern
gfp_t gfp_mask- allocation mask
int flags- search flags
Description
Looks up the search algorithm module and creates a new textsearch configuration for the specified pattern.
Returns a new textsearch configuration according to the specified parameters or a ERR_PTR(). If a zero length pattern is passed, this function returns EINVAL.
Note
- The format of the pattern may not be compatible between
- the various search algorithms.
-
void
textsearch_destroy(struct ts_config *conf)¶ destroy a search configuration
Parameters
struct ts_config *conf- search configuration
Description
Releases all references of the configuration and frees up the memory.
-
unsigned int
textsearch_next(struct ts_config *conf, struct ts_state *state)¶ continue searching for a pattern
Parameters
struct ts_config *conf- search configuration
struct ts_state *state- search state
Description
Continues a search looking for more occurrences of the pattern.
textsearch_find() must be called to find the first occurrence
in order to reset the state.
Returns the position of the next occurrence of the pattern or UINT_MAX if not match was found.
-
unsigned int
textsearch_find(struct ts_config *conf, struct ts_state *state)¶ start searching for a pattern
Parameters
struct ts_config *conf- search configuration
struct ts_state *state- search state
Description
Returns the position of first occurrence of the pattern or UINT_MAX if no match was found.
-
void *
textsearch_get_pattern(struct ts_config *conf)¶ return head of the pattern
Parameters
struct ts_config *conf- search configuration
-
unsigned int
textsearch_get_pattern_len(struct ts_config *conf)¶ return length of the pattern
Parameters
struct ts_config *conf- search configuration
CRC and Math Functions in Linux¶
CRC Functions¶
-
uint8_t
crc4(uint8_t c, uint64_t x, int bits)¶ calculate the 4-bit crc of a value.
Parameters
uint8_t c- starting crc4
uint64_t x- value to checksum
int bits- number of bits in x to checksum
Description
Returns the crc4 value of x, using polynomial 0b10111.
The x value is treated as left-aligned, and bits above bits are ignored in the crc calculations.
-
u8
crc7_be(u8 crc, const u8 *buffer, size_t len)¶ update the CRC7 for the data buffer
Parameters
u8 crc- previous CRC7 value
const u8 *buffer- data pointer
size_t len- number of bytes in the buffer
Context
any
Description
Returns the updated CRC7 value. The CRC7 is left-aligned in the byte (the lsbit is always 0), as that makes the computation easier, and all callers want it in that form.
-
void
crc8_populate_msb(u8 table[CRC8_TABLE_SIZE], u8 polynomial)¶ fill crc table for given polynomial in reverse bit order.
Parameters
u8 table[CRC8_TABLE_SIZE]- table to be filled.
u8 polynomial- polynomial for which table is to be filled.
-
void
crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE], u8 polynomial)¶ fill crc table for given polynomial in regular bit order.
Parameters
u8 table[CRC8_TABLE_SIZE]- table to be filled.
u8 polynomial- polynomial for which table is to be filled.
-
u8
crc8(const u8 table[CRC8_TABLE_SIZE], u8 *pdata, size_t nbytes, u8 crc)¶ calculate a crc8 over the given input data.
Parameters
const u8 table[CRC8_TABLE_SIZE]- crc table used for calculation.
u8 *pdata- pointer to data buffer.
size_t nbytes- number of bytes in data buffer.
u8 crc- previous returned crc8 value.
-
u16
crc16(u16 crc, u8 const *buffer, size_t len)¶ compute the CRC-16 for the data buffer
Parameters
u16 crc- previous CRC value
u8 const *buffer- data pointer
size_t len- number of bytes in the buffer
Description
Returns the updated CRC value.
-
u32 __pure
crc32_le_generic(u32 crc, unsigned char const *p, size_t len, const u32 (*tab)[256], u32 polynomial)¶ Calculate bitwise little-endian Ethernet AUTODIN II CRC32/CRC32C
Parameters
u32 crc- seed value for computation. ~0 for Ethernet, sometimes 0 for other uses, or the previous crc32/crc32c value if computing incrementally.
unsigned char const *p- pointer to buffer over which CRC32/CRC32C is run
size_t len- length of buffer p
const u32 (*tab)[256]- little-endian Ethernet table
u32 polynomial- CRC32/CRC32c LE polynomial
-
u32 __attribute_const__
crc32_generic_shift(u32 crc, size_t len, u32 polynomial)¶ Append len 0 bytes to crc, in logarithmic time
Parameters
u32 crc- The original little-endian CRC (i.e. lsbit is x^31 coefficient)
size_t len- The number of bytes. crc is multiplied by x^(8***len**)
u32 polynomial- The modulus used to reduce the result to 32 bits.
Description
It’s possible to parallelize CRC computations by computing a CRC over separate ranges of a buffer, then summing them. This shifts the given CRC by 8*len bits (i.e. produces the same effect as appending len bytes of zero to the data), in time proportional to log(len).
-
u32 __pure
crc32_be_generic(u32 crc, unsigned char const *p, size_t len, const u32 (*tab)[256], u32 polynomial)¶ Calculate bitwise big-endian Ethernet AUTODIN II CRC32
Parameters
u32 crc- seed value for computation. ~0 for Ethernet, sometimes 0 for other uses, or the previous crc32 value if computing incrementally.
unsigned char const *p- pointer to buffer over which CRC32 is run
size_t len- length of buffer p
const u32 (*tab)[256]- big-endian Ethernet table
u32 polynomial- CRC32 BE polynomial
-
u16
crc_ccitt(u16 crc, u8 const *buffer, size_t len)¶ recompute the CRC (CRC-CCITT variant) for the data buffer
Parameters
u16 crc- previous CRC value
u8 const *buffer- data pointer
size_t len- number of bytes in the buffer
-
u16
crc_ccitt_false(u16 crc, u8 const *buffer, size_t len)¶ recompute the CRC (CRC-CCITT-FALSE variant) for the data buffer
Parameters
u16 crc- previous CRC value
u8 const *buffer- data pointer
size_t len- number of bytes in the buffer
-
u16
crc_itu_t(u16 crc, const u8 *buffer, size_t len)¶ Compute the CRC-ITU-T for the data buffer
Parameters
u16 crc- previous CRC value
const u8 *buffer- data pointer
size_t len- number of bytes in the buffer
Description
Returns the updated CRC value
Base 2 log and power Functions¶
-
bool
is_power_of_2(unsigned long n)¶ check if a value is a power of two
Parameters
unsigned long n- the value to check
Description
Determine whether some value is a power of two, where zero is not considered a power of two.
Return
true if n is a power of 2, otherwise false.
-
unsigned long
__roundup_pow_of_two(unsigned long n)¶ round up to nearest power of two
Parameters
unsigned long n- value to round up
-
unsigned long
__rounddown_pow_of_two(unsigned long n)¶ round down to nearest power of two
Parameters
unsigned long n- value to round down
-
const_ilog2(n)¶ log base 2 of 32-bit or a 64-bit constant unsigned value
Parameters
n- parameter
Description
Use this where sparse expects a true constant expression, e.g. for array indices.
-
ilog2(n)¶ log base 2 of 32-bit or a 64-bit unsigned value
Parameters
n- parameter
Description
constant-capable log of base 2 calculation - this can be used to initialise global variables from constant data, hence the massive ternary operator construction
selects the appropriately-sized optimised version depending on sizeof(n)
-
roundup_pow_of_two(n)¶ round the given value up to nearest power of two
Parameters
n- parameter
Description
round the given value up to the nearest power of two - the result is undefined when n == 0 - this can be used to initialise global variables from constant data
-
rounddown_pow_of_two(n)¶ round the given value down to nearest power of two
Parameters
n- parameter
Description
round the given value down to the nearest power of two - the result is undefined when n == 0 - this can be used to initialise global variables from constant data
-
order_base_2(n)¶ calculate the (rounded up) base 2 order of the argument
Parameters
n- parameter
Description
- The first few values calculated by this routine:
- ob2(0) = 0 ob2(1) = 0 ob2(2) = 1 ob2(3) = 2 ob2(4) = 2 ob2(5) = 3 … and so on.
-
bits_per(n)¶ calculate the number of bits required for the argument
Parameters
n- parameter
Description
This is constant-capable and can be used for compile time initializations, e.g bitfields.
The first few values calculated by this routine: bf(0) = 1 bf(1) = 1 bf(2) = 2 bf(3) = 2 bf(4) = 3 … and so on.
Integer power Functions¶
-
u64
int_pow(u64 base, unsigned int exp)¶ computes the exponentiation of the given base and exponent
Parameters
u64 base- base which will be raised to the given power
unsigned int exp- power to be raised to
Description
Computes: pow(base, exp), i.e. base raised to the exp power
-
unsigned long
int_sqrt(unsigned long x)¶ computes the integer square root
Parameters
unsigned long x- integer of which to calculate the sqrt
Description
Computes: floor(sqrt(x))
-
u32
int_sqrt64(u64 x)¶ strongly typed int_sqrt function when minimum 64 bit input is expected.
Parameters
u64 x- 64bit integer of which to calculate the sqrt
Division Functions¶
-
do_div(n, base)¶ returns 2 values: calculate remainder and update new dividend
Parameters
n- uint64_t dividend (will be updated)
base- uint32_t divisor
Description
Summary:
uint32_t remainder = n % base;
n = n / base;
Return
(uint32_t)remainder
NOTE
macro parameter n is evaluated multiple times, beware of side effects!
-
u64
div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)¶ unsigned 64bit divide with 32bit divisor with remainder
Parameters
u64 dividend- unsigned 64bit dividend
u32 divisor- unsigned 32bit divisor
u32 *remainder- pointer to unsigned 32bit remainder
Return
sets *remainder, then returns dividend / divisor
Description
This is commonly provided by 32bit archs to provide an optimized 64bit divide.
-
u64
div_u64(u64 dividend, u32 divisor)¶ unsigned 64bit divide with 32bit divisor
Parameters
u64 dividend- unsigned 64bit dividend
u32 divisor- unsigned 32bit divisor
Description
This is the most common 64bit divide and should be used if possible, as many 32bit archs can optimize this variant better than a full 64bit divide.
-
s64
div_s64(s64 dividend, s32 divisor)¶ signed 64bit divide with 32bit divisor
Parameters
s64 dividend- signed 64bit dividend
s32 divisor- signed 32bit divisor
-
DIV64_U64_ROUND_CLOSEST(dividend, divisor)¶ unsigned 64bit divide with 64bit divisor rounded to nearest integer
Parameters
dividend- unsigned 64bit dividend
divisor- unsigned 64bit divisor
Description
Divide unsigned 64bit dividend by unsigned 64bit divisor and round to closest integer.
Return
dividend / divisor rounded to nearest integer
-
s64
div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)¶ signed 64bit divide with 64bit divisor and remainder
Parameters
s64 dividend- 64bit dividend
s32 divisor- 64bit divisor
s32 *remainder- 64bit remainder
-
u64
div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)¶ unsigned 64bit divide with 64bit divisor and remainder
Parameters
u64 dividend- 64bit dividend
u64 divisor- 64bit divisor
u64 *remainder- 64bit remainder
Description
This implementation is a comparable to algorithm used by div64_u64. But this operation, which includes math for calculating the remainder, is kept distinct to avoid slowing down the div64_u64 operation on 32bit systems.
-
u64
div64_u64(u64 dividend, u64 divisor)¶ unsigned 64bit divide with 64bit divisor
Parameters
u64 dividend- 64bit dividend
u64 divisor- 64bit divisor
Description
This implementation is a modified version of the algorithm proposed by the book ‘Hacker’s Delight’. The original source and full proof can be found here and is available for use without restriction.
‘http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt’
-
s64
div64_s64(s64 dividend, s64 divisor)¶ signed 64bit divide with 64bit divisor
Parameters
s64 dividend- 64bit dividend
s64 divisor- 64bit divisor
-
unsigned long
gcd(unsigned long a, unsigned long b)¶ calculate and return the greatest common divisor of 2 unsigned longs
Parameters
unsigned long a- first value
unsigned long b- second value
UUID/GUID¶
-
void
generate_random_uuid(unsigned char uuid[16])¶ generate a random UUID
Parameters
unsigned char uuid[16]- where to put the generated UUID
Description
Random UUID interface
Used to create a Boot ID or a filesystem UUID/GUID, but can be useful for other kernel drivers.
-
bool
uuid_is_valid(const char *uuid)¶ checks if a UUID string is valid
Parameters
const char *uuid- UUID string to check
Description
- It checks if the UUID string is following the format:
- xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
where x is a hex digit.
Return
true if input is valid UUID string.
Kernel IPC facilities¶
IPC utilities¶
-
int
ipc_init(void)¶ initialise ipc subsystem
Parameters
void- no arguments
Description
The various sysv ipc resources (semaphores, messages and shared memory) are initialised.
A callback routine is registered into the memory hotplug notifier chain: since msgmni scales to lowmem this callback routine will be called upon successful memory add / remove to recompute msmgni.
-
void
ipc_init_ids(struct ipc_ids *ids)¶ initialise ipc identifiers
Parameters
struct ipc_ids *ids- ipc identifier set
Description
Set up the sequence range to use for the ipc identifier range (limited below ipc_mni) then initialise the keys hashtable and ids idr.
-
void
ipc_init_proc_interface(const char *path, const char *header, int ids, int (*show)(struct seq_file *, void *))¶ create a proc interface for sysipc types using a seq_file interface.
Parameters
const char *path- Path in procfs
const char *header- Banner to be printed at the beginning of the file.
int ids- ipc id table to iterate.
int (*show)(struct seq_file *, void *)- show routine.
-
struct kern_ipc_perm *
ipc_findkey(struct ipc_ids *ids, key_t key)¶ find a key in an ipc identifier set
Parameters
struct ipc_ids *ids- ipc identifier set
key_t key- key to find
Description
Returns the locked pointer to the ipc structure if found or NULL otherwise. If key is found ipc points to the owning ipc structure
Called with writer ipc_ids.rwsem held.
-
int
ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)¶ add an ipc identifier
Parameters
struct ipc_ids *ids- ipc identifier set
struct kern_ipc_perm *new- new ipc permission set
int limit- limit for the number of used ids
Description
Add an entry ‘new’ to the ipc ids idr. The permissions object is initialised and the first free entry is set up and the index assigned is returned. The ‘new’ entry is returned in a locked state on success.
On failure the entry is not locked and a negative err-code is returned. The caller must use ipc_rcu_putref() to free the identifier.
Called with writer ipc_ids.rwsem held.
-
int
ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids, const struct ipc_ops *ops, struct ipc_params *params)¶ create a new ipc object
Parameters
struct ipc_namespace *ns- ipc namespace
struct ipc_ids *ids- ipc identifier set
const struct ipc_ops *ops- the actual creation routine to call
struct ipc_params *params- its parameters
Description
This routine is called by sys_msgget, sys_semget() and sys_shmget() when the key is IPC_PRIVATE.
-
int
ipc_check_perms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, const struct ipc_ops *ops, struct ipc_params *params)¶ check security and permissions for an ipc object
Parameters
struct ipc_namespace *ns- ipc namespace
struct kern_ipc_perm *ipcp- ipc permission set
const struct ipc_ops *ops- the actual security routine to call
struct ipc_params *params- its parameters
Description
This routine is called by sys_msgget(), sys_semget() and sys_shmget() when the key is not IPC_PRIVATE and that key already exists in the ds IDR.
On success, the ipc id is returned.
It is called with ipc_ids.rwsem and ipcp->lock held.
-
int
ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids, const struct ipc_ops *ops, struct ipc_params *params)¶ get an ipc object or create a new one
Parameters
struct ipc_namespace *ns- ipc namespace
struct ipc_ids *ids- ipc identifier set
const struct ipc_ops *ops- the actual creation routine to call
struct ipc_params *params- its parameters
Description
This routine is called by sys_msgget, sys_semget() and sys_shmget() when the key is not IPC_PRIVATE. It adds a new entry if the key is not found and does some permission / security checkings if the key is found.
On success, the ipc id is returned.
-
void
ipc_kht_remove(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)¶ remove an ipc from the key hashtable
Parameters
struct ipc_ids *ids- ipc identifier set
struct kern_ipc_perm *ipcp- ipc perm structure containing the key to remove
Description
ipc_ids.rwsem (as a writer) and the spinlock for this ID are held before this function is called, and remain locked on the exit.
-
void
ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)¶ remove an ipc identifier
Parameters
struct ipc_ids *ids- ipc identifier set
struct kern_ipc_perm *ipcp- ipc perm structure containing the identifier to remove
Description
ipc_ids.rwsem (as a writer) and the spinlock for this ID are held before this function is called, and remain locked on the exit.
-
void
ipc_set_key_private(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)¶ switch the key of an existing ipc to IPC_PRIVATE
Parameters
struct ipc_ids *ids- ipc identifier set
struct kern_ipc_perm *ipcp- ipc perm structure containing the key to modify
Description
ipc_ids.rwsem (as a writer) and the spinlock for this ID are held before this function is called, and remain locked on the exit.
-
int
ipcperms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, short flag)¶ check ipc permissions
Parameters
struct ipc_namespace *ns- ipc namespace
struct kern_ipc_perm *ipcp- ipc permission set
short flag- desired permission set
Description
Check user, group, other permissions for access to ipc resources. return 0 if allowed
flag will most probably be 0 or S_...UGO from <linux/stat.h>
-
void
kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out)¶ convert kernel ipc permissions to user
Parameters
struct kern_ipc_perm *in- kernel permissions
struct ipc64_perm *out- new style ipc permissions
Description
Turn the kernel object in into a set of permissions descriptions for returning to userspace (out).
-
void
ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out)¶ convert new ipc permissions to old
Parameters
struct ipc64_perm *in- new style ipc permissions
struct ipc_perm *out- old style ipc permissions
Description
Turn the new style permissions object in into a compatibility object and store it into the out pointer.
-
struct kern_ipc_perm *
ipc_obtain_object_idr(struct ipc_ids *ids, int id)¶
Parameters
struct ipc_ids *ids- ipc identifier set
int id- ipc id to look for
Description
Look for an id in the ipc ids idr and return associated ipc object.
Call inside the RCU critical section. The ipc object is not locked on exit.
-
struct kern_ipc_perm *
ipc_obtain_object_check(struct ipc_ids *ids, int id)¶
Parameters
struct ipc_ids *ids- ipc identifier set
int id- ipc id to look for
Description
Similar to ipc_obtain_object_idr() but also checks the ipc object
sequence number.
Call inside the RCU critical section. The ipc object is not locked on exit.
-
int
ipcget(struct ipc_namespace *ns, struct ipc_ids *ids, const struct ipc_ops *ops, struct ipc_params *params)¶ Common sys_*get() code
Parameters
struct ipc_namespace *ns- namespace
struct ipc_ids *ids- ipc identifier set
const struct ipc_ops *ops- operations to be called on ipc object creation, permission checks and further checks
struct ipc_params *params- the parameters needed by the previous operations.
Description
Common routine called by sys_msgget(), sys_semget() and sys_shmget().
-
int
ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)¶ update the permissions of an ipc object
Parameters
struct ipc64_perm *in- the permission given as input.
struct kern_ipc_perm *out- the permission of the ipc to set.
-
struct kern_ipc_perm *
ipcctl_obtain_check(struct ipc_namespace *ns, struct ipc_ids *ids, int id, int cmd, struct ipc64_perm *perm, int extra_perm)¶ retrieve an ipc object and check permissions
Parameters
struct ipc_namespace *ns- ipc namespace
struct ipc_ids *ids- the table of ids where to look for the ipc
int id- the id of the ipc to retrieve
int cmd- the cmd to check
struct ipc64_perm *perm- the permission to set
int extra_perm- one extra permission parameter used by msq
Description
This function does some common audit and permissions check for some IPC_XXX cmd and is called from semctl_down, shmctl_down and msgctl_down.
- It:
- retrieves the ipc object with the given id in the given table.
- performs some audit and permission check, depending on the given cmd
- returns a pointer to the ipc object or otherwise, the corresponding error.
Call holding the both the rwsem and the rcu read lock.
-
int
ipc_parse_version(int *cmd)¶ ipc call version
Parameters
int *cmd- pointer to command
Description
Return IPC_64 for new style IPC and IPC_OLD for old style IPC. The cmd value is turned from an encoding command and version into just the command code.
FIFO Buffer¶
kfifo interface¶
-
DECLARE_KFIFO_PTR(fifo, type)¶ macro to declare a fifo pointer object
Parameters
fifo- name of the declared fifo
type- type of the fifo elements
-
DECLARE_KFIFO(fifo, type, size)¶ macro to declare a fifo object
Parameters
fifo- name of the declared fifo
type- type of the fifo elements
size- the number of elements in the fifo, this must be a power of 2
-
INIT_KFIFO(fifo)¶ Initialize a fifo declared by DECLARE_KFIFO
Parameters
fifo- name of the declared fifo datatype
-
DEFINE_KFIFO(fifo, type, size)¶ macro to define and initialize a fifo
Parameters
fifo- name of the declared fifo datatype
type- type of the fifo elements
size- the number of elements in the fifo, this must be a power of 2
Note
the macro can be used for global and local fifo data type variables.
-
kfifo_initialized(fifo)¶ Check if the fifo is initialized
Parameters
fifo- address of the fifo to check
Description
Return true if fifo is initialized, otherwise false.
Assumes the fifo was 0 before.
-
kfifo_esize(fifo)¶ returns the size of the element managed by the fifo
Parameters
fifo- address of the fifo to be used
-
kfifo_recsize(fifo)¶ returns the size of the record length field
Parameters
fifo- address of the fifo to be used
-
kfifo_size(fifo)¶ returns the size of the fifo in elements
Parameters
fifo- address of the fifo to be used
-
kfifo_reset(fifo)¶ removes the entire fifo content
Parameters
fifo- address of the fifo to be used
Note
usage of kfifo_reset() is dangerous. It should be only called when the
fifo is exclusived locked or when it is secured that no other thread is
accessing the fifo.
-
kfifo_reset_out(fifo)¶ skip fifo content
Parameters
fifo- address of the fifo to be used
Note
The usage of kfifo_reset_out() is safe until it will be only called
from the reader thread and there is only one concurrent reader. Otherwise
it is dangerous and must be handled in the same way as kfifo_reset().
-
kfifo_len(fifo)¶ returns the number of used elements in the fifo
Parameters
fifo- address of the fifo to be used
-
kfifo_is_empty(fifo)¶ returns true if the fifo is empty
Parameters
fifo- address of the fifo to be used
-
kfifo_is_empty_spinlocked(fifo, lock)¶ returns true if the fifo is empty using a spinlock for locking
Parameters
fifo- address of the fifo to be used
lock- spinlock to be used for locking
-
kfifo_is_empty_spinlocked_noirqsave(fifo, lock)¶ returns true if the fifo is empty using a spinlock for locking, doesn’t disable interrupts
Parameters
fifo- address of the fifo to be used
lock- spinlock to be used for locking
-
kfifo_is_full(fifo)¶ returns true if the fifo is full
Parameters
fifo- address of the fifo to be used
-
kfifo_avail(fifo)¶ returns the number of unused elements in the fifo
Parameters
fifo- address of the fifo to be used
-
kfifo_skip(fifo)¶ skip output data
Parameters
fifo- address of the fifo to be used
-
kfifo_peek_len(fifo)¶ gets the size of the next fifo record
Parameters
fifo- address of the fifo to be used
Description
This function returns the size of the next fifo record in number of bytes.
-
kfifo_alloc(fifo, size, gfp_mask)¶ dynamically allocates a new fifo buffer
Parameters
fifo- pointer to the fifo
size- the number of elements in the fifo, this must be a power of 2
gfp_mask- get_free_pages mask, passed to
kmalloc()
Description
This macro dynamically allocates a new fifo buffer.
The number of elements will be rounded-up to a power of 2.
The fifo will be release with kfifo_free().
Return 0 if no error, otherwise an error code.
-
kfifo_free(fifo)¶ frees the fifo
Parameters
fifo- the fifo to be freed
-
kfifo_init(fifo, buffer, size)¶ initialize a fifo using a preallocated buffer
Parameters
fifo- the fifo to assign the buffer
buffer- the preallocated buffer to be used
size- the size of the internal buffer, this have to be a power of 2
Description
This macro initializes a fifo using a preallocated buffer.
The number of elements will be rounded-up to a power of 2. Return 0 if no error, otherwise an error code.
-
kfifo_put(fifo, val)¶ put data into the fifo
Parameters
fifo- address of the fifo to be used
val- the data to be added
Description
This macro copies the given value into the fifo. It returns 0 if the fifo was full. Otherwise it returns the number processed elements.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macro.
-
kfifo_get(fifo, val)¶ get data from the fifo
Parameters
fifo- address of the fifo to be used
val- address where to store the data
Description
This macro reads the data from the fifo. It returns 0 if the fifo was empty. Otherwise it returns the number processed elements.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macro.
-
kfifo_peek(fifo, val)¶ get data from the fifo without removing
Parameters
fifo- address of the fifo to be used
val- address where to store the data
Description
This reads the data from the fifo without removing it from the fifo. It returns 0 if the fifo was empty. Otherwise it returns the number processed elements.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macro.
-
kfifo_in(fifo, buf, n)¶ put data into the fifo
Parameters
fifo- address of the fifo to be used
buf- the data to be added
n- number of elements to be added
Description
This macro copies the given buffer into the fifo and returns the number of copied elements.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macro.
-
kfifo_in_spinlocked(fifo, buf, n, lock)¶ put data into the fifo using a spinlock for locking
Parameters
fifo- address of the fifo to be used
buf- the data to be added
n- number of elements to be added
lock- pointer to the spinlock to use for locking
Description
This macro copies the given values buffer into the fifo and returns the number of copied elements.
-
kfifo_in_spinlocked_noirqsave(fifo, buf, n, lock)¶ put data into fifo using a spinlock for locking, don’t disable interrupts
Parameters
fifo- address of the fifo to be used
buf- the data to be added
n- number of elements to be added
lock- pointer to the spinlock to use for locking
Description
This is a variant of kfifo_in_spinlocked() but uses spin_lock/unlock()
for locking and doesn’t disable interrupts.
-
kfifo_out(fifo, buf, n)¶ get data from the fifo
Parameters
fifo- address of the fifo to be used
buf- pointer to the storage buffer
n- max. number of elements to get
Description
This macro get some data from the fifo and return the numbers of elements copied.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macro.
-
kfifo_out_spinlocked(fifo, buf, n, lock)¶ get data from the fifo using a spinlock for locking
Parameters
fifo- address of the fifo to be used
buf- pointer to the storage buffer
n- max. number of elements to get
lock- pointer to the spinlock to use for locking
Description
This macro get the data from the fifo and return the numbers of elements copied.
-
kfifo_out_spinlocked_noirqsave(fifo, buf, n, lock)¶ get data from the fifo using a spinlock for locking, don’t disable interrupts
Parameters
fifo- address of the fifo to be used
buf- pointer to the storage buffer
n- max. number of elements to get
lock- pointer to the spinlock to use for locking
Description
This is a variant of kfifo_out_spinlocked() which uses spin_lock/unlock()
for locking and doesn’t disable interrupts.
-
kfifo_from_user(fifo, from, len, copied)¶ puts some data from user space into the fifo
Parameters
fifo- address of the fifo to be used
from- pointer to the data to be added
len- the length of the data to be added
copied- pointer to output variable to store the number of copied bytes
Description
This macro copies at most len bytes from the from into the fifo, depending of the available space and returns -EFAULT/0.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macro.
-
kfifo_to_user(fifo, to, len, copied)¶ copies data from the fifo into user space
Parameters
fifo- address of the fifo to be used
to- where the data must be copied
len- the size of the destination buffer
copied- pointer to output variable to store the number of copied bytes
Description
This macro copies at most len bytes from the fifo into the to buffer and returns -EFAULT/0.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macro.
-
kfifo_dma_in_prepare(fifo, sgl, nents, len)¶ setup a scatterlist for DMA input
Parameters
fifo- address of the fifo to be used
sgl- pointer to the scatterlist array
nents- number of entries in the scatterlist array
len- number of elements to transfer
Description
This macro fills a scatterlist for DMA input. It returns the number entries in the scatterlist array.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macros.
-
kfifo_dma_in_finish(fifo, len)¶ finish a DMA IN operation
Parameters
fifo- address of the fifo to be used
len- number of bytes to received
Description
This macro finish a DMA IN operation. The in counter will be updated by the len parameter. No error checking will be done.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macros.
-
kfifo_dma_out_prepare(fifo, sgl, nents, len)¶ setup a scatterlist for DMA output
Parameters
fifo- address of the fifo to be used
sgl- pointer to the scatterlist array
nents- number of entries in the scatterlist array
len- number of elements to transfer
Description
This macro fills a scatterlist for DMA output which at most len bytes to transfer. It returns the number entries in the scatterlist array. A zero means there is no space available and the scatterlist is not filled.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macros.
-
kfifo_dma_out_finish(fifo, len)¶ finish a DMA OUT operation
Parameters
fifo- address of the fifo to be used
len- number of bytes transferred
Description
This macro finish a DMA OUT operation. The out counter will be updated by the len parameter. No error checking will be done.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macros.
-
kfifo_out_peek(fifo, buf, n)¶ gets some data from the fifo
Parameters
fifo- address of the fifo to be used
buf- pointer to the storage buffer
n- max. number of elements to get
Description
This macro get the data from the fifo and return the numbers of elements copied. The data is not removed from the fifo.
Note that with only one concurrent reader and one concurrent writer, you don’t need extra locking to use these macro.
relay interface support¶
Relay interface support is designed to provide an efficient mechanism for tools and facilities to relay large amounts of data from kernel space to user space.
relay interface¶
-
int
relay_buf_full(struct rchan_buf *buf)¶ boolean, is the channel buffer full?
Parameters
struct rchan_buf *bufchannel buffer
Returns 1 if the buffer is full, 0 otherwise.
-
void
relay_reset(struct rchan *chan)¶ reset the channel
Parameters
struct rchan *chanthe channel
This has the effect of erasing all data from all channel buffers and restarting the channel in its initial state. The buffers are not freed, so any mappings are still in effect.
NOTE. Care should be taken that the channel isn’t actually being used by anything when this call is made.
-
struct rchan *
relay_open(const char *base_filename, struct dentry *parent, size_t subbuf_size, size_t n_subbufs, const struct rchan_callbacks *cb, void *private_data)¶ create a new relay channel
Parameters
const char *base_filename- base name of files to create,
NULLfor buffering only struct dentry *parent- dentry of parent directory,
NULLfor root directory or buffer size_t subbuf_size- size of sub-buffers
size_t n_subbufs- number of sub-buffers
const struct rchan_callbacks *cb- client callback functions
void *private_datauser-defined data
Returns channel pointer if successful,
NULLotherwise.Creates a channel buffer for each cpu using the sizes and attributes specified. The created channel buffer files will be named base_filename0…base_filenameN-1. File permissions will be
S_IRUSR.If opening a buffer (parent = NULL) that you later wish to register in a filesystem, call
relay_late_setup_files()once the parent dentry is available.
-
int
relay_late_setup_files(struct rchan *chan, const char *base_filename, struct dentry *parent)¶ triggers file creation
Parameters
struct rchan *chan- channel to operate on
const char *base_filename- base name of files to create
struct dentry *parentdentry of parent directory,
NULLfor root directoryReturns 0 if successful, non-zero otherwise.
Use to setup files for a previously buffer-only channel created by
relay_open()with a NULL parent dentry.For example, this is useful for perfomring early tracing in kernel, before VFS is up and then exposing the early results once the dentry is available.
-
size_t
relay_switch_subbuf(struct rchan_buf *buf, size_t length)¶ switch to a new sub-buffer
Parameters
struct rchan_buf *buf- channel buffer
size_t lengthsize of current event
Returns either the length passed in or 0 if full.
Performs sub-buffer-switch tasks such as invoking callbacks, updating padding counts, waking up readers, etc.
-
void
relay_subbufs_consumed(struct rchan *chan, unsigned int cpu, size_t subbufs_consumed)¶ update the buffer’s sub-buffers-consumed count
Parameters
struct rchan *chan- the channel
unsigned int cpu- the cpu associated with the channel buffer to update
size_t subbufs_consumednumber of sub-buffers to add to current buf’s count
Adds to the channel buffer’s consumed sub-buffer count. subbufs_consumed should be the number of sub-buffers newly consumed, not the total consumed.
NOTE. Kernel clients don’t need to call this function if the channel mode is ‘overwrite’.
-
void
relay_close(struct rchan *chan)¶ close the channel
Parameters
struct rchan *chanthe channel
Closes all channel buffers and frees the channel.
-
void
relay_flush(struct rchan *chan)¶ close the channel
Parameters
struct rchan *chanthe channel
Flushes all channel buffers, i.e. forces buffer switch.
-
int
relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)¶ mmap channel buffer to process address space
Parameters
struct rchan_buf *buf- relay channel buffer
struct vm_area_struct *vmavm_area_struct describing memory to be mapped
Returns 0 if ok, negative on error
Caller should already have grabbed mmap_lock.
-
void *
relay_alloc_buf(struct rchan_buf *buf, size_t *size)¶ allocate a channel buffer
Parameters
struct rchan_buf *buf- the buffer struct
size_t *sizetotal size of the buffer
Returns a pointer to the resulting buffer,
NULLif unsuccessful. The passed in size will get page aligned, if it isn’t already.
-
struct rchan_buf *
relay_create_buf(struct rchan *chan)¶ allocate and initialize a channel buffer
Parameters
struct rchan *chanthe relay channel
Returns channel buffer if successful,
NULLotherwise.
-
void
relay_destroy_channel(struct kref *kref)¶ free the channel struct
Parameters
struct kref *kreftarget kernel reference that contains the relay channel
Should only be called from kref_put().
-
void
relay_destroy_buf(struct rchan_buf *buf)¶ destroy an rchan_buf struct and associated buffer
Parameters
struct rchan_buf *buf- the buffer struct
-
void
relay_remove_buf(struct kref *kref)¶ remove a channel buffer
Parameters
struct kref *kreftarget kernel reference that contains the relay buffer
Removes the file from the filesystem, which also frees the rchan_buf_struct and the channel buffer. Should only be called from kref_put().
-
int
relay_buf_empty(struct rchan_buf *buf)¶ boolean, is the channel buffer empty?
Parameters
struct rchan_buf *bufchannel buffer
Returns 1 if the buffer is empty, 0 otherwise.
-
void
wakeup_readers(struct irq_work *work)¶ wake up readers waiting on a channel
Parameters
struct irq_work *workcontains the channel buffer
This is the function used to defer reader waking
-
void
__relay_reset(struct rchan_buf *buf, unsigned int init)¶ reset a channel buffer
Parameters
struct rchan_buf *buf- the channel buffer
unsigned int init1 if this is a first-time initialization
See
relay_reset()for description of effect.
-
void
relay_close_buf(struct rchan_buf *buf)¶ close a channel buffer
Parameters
struct rchan_buf *bufchannel buffer
Marks the buffer finalized and restores the default callbacks. The channel buffer and channel buffer data structure are then freed automatically when the last reference is given up.
-
int
relay_file_open(struct inode *inode, struct file *filp)¶ open file op for relay files
Parameters
struct inode *inode- the inode
struct file *filpthe file
Increments the channel buffer refcount.
-
int
relay_file_mmap(struct file *filp, struct vm_area_struct *vma)¶ mmap file op for relay files
Parameters
struct file *filp- the file
struct vm_area_struct *vmathe vma describing what to map
Calls upon
relay_mmap_buf()to map the file into user space.
-
__poll_t
relay_file_poll(struct file *filp, poll_table *wait)¶ poll file op for relay files
Parameters
struct file *filp- the file
poll_table *waitpoll table
Poll implemention.
-
int
relay_file_release(struct inode *inode, struct file *filp)¶ release file op for relay files
Parameters
struct inode *inode- the inode
struct file *filpthe file
Decrements the channel refcount, as the filesystem is no longer using it.
-
size_t
relay_file_read_subbuf_avail(size_t read_pos, struct rchan_buf *buf)¶ return bytes available in sub-buffer
Parameters
size_t read_pos- file read position
struct rchan_buf *buf- relay channel buffer
-
size_t
relay_file_read_start_pos(struct rchan_buf *buf)¶ find the first available byte to read
Parameters
struct rchan_buf *bufrelay channel buffer
If the read_pos is in the middle of padding, return the position of the first actually available byte, otherwise return the original value.
-
size_t
relay_file_read_end_pos(struct rchan_buf *buf, size_t read_pos, size_t count)¶ return the new read position
Parameters
struct rchan_buf *buf- relay channel buffer
size_t read_pos- file read position
size_t count- number of bytes to be read
Module Support¶
Module Loading¶
-
int
__request_module(bool wait, const char *fmt, ...)¶ try to load a kernel module
Parameters
bool wait- wait (or not) for the operation to complete
const char *fmt- printf style format string for the name of the module
...- arguments as specified in the format string
Description
Load a module using the user mode module loader. The function returns zero on success or a negative errno code or positive exit code from “modprobe” on failure. Note that a successful module load does not mean the module did not then unload and exit on an error of its own. Callers must check that the service they requested is now available not blindly invoke it.
If module auto-loading support is disabled then this function simply returns -ENOENT.
Inter Module support¶
Refer to the file kernel/module.c for more information.
Hardware Interfaces¶
DMA Channels¶
-
int
request_dma(unsigned int dmanr, const char * device_id)¶ request and reserve a system DMA channel
Parameters
unsigned int dmanr- DMA channel number
const char * device_id- reserving device ID string, used in /proc/dma
-
void
free_dma(unsigned int dmanr)¶ free a reserved system DMA channel
Parameters
unsigned int dmanr- DMA channel number
Resources Management¶
-
struct resource *
request_resource_conflict(struct resource *root, struct resource *new)¶ request and reserve an I/O or memory resource
Parameters
struct resource *root- root resource descriptor
struct resource *new- resource descriptor desired by caller
Description
Returns 0 for success, conflict resource on error.
-
int
find_next_iomem_res(resource_size_t start, resource_size_t end, unsigned long flags, unsigned long desc, bool first_lvl, struct resource *res)¶ Finds the lowest iomem resource that covers part of [start..**end**].
Parameters
resource_size_t start- start address of the resource searched for
resource_size_t end- end address of same resource
unsigned long flags- flags which the resource must have
unsigned long desc- descriptor the resource must have
bool first_lvl- walk only the first level children, if set
struct resource *res- return ptr, if resource found
Description
If a resource is found, returns 0 and ***res is overwritten with the part of the resource that’s within [**start..**end**]; if none is found, returns -ENODEV. Returns -EINVAL for invalid parameters.
This function walks the whole tree and not just first level children unless first_lvl is true.
The caller must specify start, end, flags, and desc (which may be IORES_DESC_NONE).
-
int
reallocate_resource(struct resource *root, struct resource *old, resource_size_t newsize, struct resource_constraint *constraint)¶ allocate a slot in the resource tree given range & alignment. The resource will be relocated if the new size cannot be reallocated in the current location.
Parameters
struct resource *root- root resource descriptor
struct resource *old- resource descriptor desired by caller
resource_size_t newsize- new size of the resource descriptor
struct resource_constraint *constraint- the size and alignment constraints to be met.
-
struct resource *
lookup_resource(struct resource *root, resource_size_t start)¶ find an existing resource by a resource start address
Parameters
struct resource *root- root resource descriptor
resource_size_t start- resource start address
Description
Returns a pointer to the resource if found, NULL otherwise
-
struct resource *
insert_resource_conflict(struct resource *parent, struct resource *new)¶ Inserts resource in the resource tree
Parameters
struct resource *parent- parent of the new resource
struct resource *new- new resource to insert
Description
Returns 0 on success, conflict resource if the resource can’t be inserted.
This function is equivalent to request_resource_conflict when no conflict happens. If a conflict happens, and the conflicting resources entirely fit within the range of the new resource, then the new resource is inserted and the conflicting resources become children of the new resource.
This function is intended for producers of resources, such as FW modules and bus drivers.
-
void
insert_resource_expand_to_fit(struct resource *root, struct resource *new)¶ Insert a resource into the resource tree
Parameters
struct resource *root- root resource descriptor
struct resource *new- new resource to insert
Description
Insert a resource into the resource tree, possibly expanding it in order to make it encompass any conflicting resources.
-
resource_size_t
resource_alignment(struct resource *res)¶ calculate resource’s alignment
Parameters
struct resource *res- resource pointer
Description
Returns alignment on success, 0 (invalid alignment) on failure.
-
void
release_mem_region_adjustable(resource_size_t start, resource_size_t size)¶ release a previously reserved memory region
Parameters
resource_size_t start- resource start address
resource_size_t size- resource region size
Description
This interface is intended for memory hot-delete. The requested region is released from a currently busy memory resource. The requested region must either match exactly or fit into a single busy resource entry. In the latter case, the remaining resource is adjusted accordingly. Existing children of the busy memory resource must be immutable in the request.
Note
- Additional release conditions, such as overlapping region, can be supported after they are confirmed as valid cases.
- When a busy memory resource gets split into two entries, the code assumes that all children remain in the lower address entry for simplicity. Enhance this logic when necessary.
-
void
merge_system_ram_resource(struct resource *res)¶ mark the System RAM resource mergeable and try to merge it with adjacent, mergeable resources
Parameters
struct resource *res- resource descriptor
Description
This interface is intended for memory hotplug, whereby lots of contiguous system ram resources are added (e.g., via add_memory*()) by a driver, and the actual resource boundaries are not of interest (e.g., it might be relevant for DIMMs). Only resources that are marked mergeable, that have the same parent, and that don’t have any children are considered. All mergeable resources must be immutable during the request.
Note
- The caller has to make sure that no pointers to resources that are marked mergeable are used anymore after this call - the resource might be freed and the pointer might be stale!
release_mem_region_adjustable()will split on demand on memory hotunplug
-
int
request_resource(struct resource *root, struct resource *new)¶ request and reserve an I/O or memory resource
Parameters
struct resource *root- root resource descriptor
struct resource *new- resource descriptor desired by caller
Description
Returns 0 for success, negative error code on error.
-
int
release_resource(struct resource *old)¶ release a previously reserved resource
Parameters
struct resource *old- resource pointer
-
int
walk_iomem_res_desc(unsigned long desc, unsigned long flags, u64 start, u64 end, void *arg, int (*func)(struct resource *, void *))¶ Walks through iomem resources and calls func() with matching resource ranges. *
Parameters
unsigned long desc- I/O resource descriptor. Use IORES_DESC_NONE to skip desc check.
unsigned long flags- I/O resource flags
u64 start- start addr
u64 end- end addr
void *arg- function argument for the callback func
int (*func)(struct resource *, void *)- callback function that is called for each qualifying resource area
Description
This walks through whole tree and not just first level children. All the memory ranges which overlap start,end and also match flags and desc are valid candidates.
NOTE
For a new descriptor search, define a new IORES_DESC in <linux/ioport.h> and set it in ‘desc’ of a target resource entry.
-
int
region_intersects(resource_size_t start, size_t size, unsigned long flags, unsigned long desc)¶ determine intersection of region with known resources
Parameters
resource_size_t start- region start address
size_t size- size of region
unsigned long flags- flags of resource (in iomem_resource)
unsigned long desc- descriptor of resource (in iomem_resource) or IORES_DESC_NONE
Description
Check if the specified region partially overlaps or fully eclipses a resource identified by flags and desc (optional with IORES_DESC_NONE). Return REGION_DISJOINT if the region does not overlap flags/desc, return REGION_MIXED if the region overlaps flags/desc and another resource, and return REGION_INTERSECTS if the region overlaps flags/desc and no other defined resource. Note that REGION_INTERSECTS is also returned in the case when the specified region overlaps RAM and undefined memory holes.
region_intersect() is used by memory remapping functions to ensure the user is not remapping RAM and is a vast speed up over walking through the resource table page by page.
-
int
allocate_resource(struct resource *root, struct resource *new, resource_size_t size, resource_size_t min, resource_size_t max, resource_size_t align, resource_size_t (*alignf)(void *, const struct resource *, resource_size_t, resource_size_t), void *alignf_data)¶ allocate empty slot in the resource tree given range & alignment. The resource will be reallocated with a new size if it was already allocated
Parameters
struct resource *root- root resource descriptor
struct resource *new- resource descriptor desired by caller
resource_size_t size- requested resource region size
resource_size_t min- minimum boundary to allocate
resource_size_t max- maximum boundary to allocate
resource_size_t align- alignment requested, in bytes
resource_size_t (*alignf)(void *, const struct resource *, resource_size_t, resource_size_t)- alignment function, optional, called if not NULL
void *alignf_data- arbitrary data to pass to the alignf function
-
int
insert_resource(struct resource *parent, struct resource *new)¶ Inserts a resource in the resource tree
Parameters
struct resource *parent- parent of the new resource
struct resource *new- new resource to insert
Description
Returns 0 on success, -EBUSY if the resource can’t be inserted.
This function is intended for producers of resources, such as FW modules and bus drivers.
-
int
remove_resource(struct resource *old)¶ Remove a resource in the resource tree
Parameters
struct resource *old- resource to remove
Description
Returns 0 on success, -EINVAL if the resource is not valid.
This function removes a resource previously inserted by insert_resource()
or insert_resource_conflict(), and moves the children (if any) up to
where they were before. insert_resource() and insert_resource_conflict()
insert a new resource, and move any conflicting resources down to the
children of the new resource.
insert_resource(), insert_resource_conflict() and remove_resource() are
intended for producers of resources, such as FW modules and bus drivers.
-
int
adjust_resource(struct resource *res, resource_size_t start, resource_size_t size)¶ modify a resource’s start and size
Parameters
struct resource *res- resource to modify
resource_size_t start- new start value
resource_size_t size- new size
Description
Given an existing resource, change its start and size to match the arguments. Returns 0 on success, -EBUSY if it can’t fit. Existing children of the resource are assumed to be immutable.
-
struct resource *
__request_region(struct resource *parent, resource_size_t start, resource_size_t n, const char *name, int flags)¶ create a new busy resource region
Parameters
struct resource *parent- parent resource descriptor
resource_size_t start- resource start address
resource_size_t n- resource region size
const char *name- reserving caller’s ID string
int flags- IO resource flags
-
void
__release_region(struct resource *parent, resource_size_t start, resource_size_t n)¶ release a previously reserved resource region
Parameters
struct resource *parent- parent resource descriptor
resource_size_t start- resource start address
resource_size_t n- resource region size
Description
The described resource region must match a currently busy region.
-
int
devm_request_resource(struct device *dev, struct resource *root, struct resource *new)¶ request and reserve an I/O or memory resource
Parameters
struct device *dev- device for which to request the resource
struct resource *root- root of the resource tree from which to request the resource
struct resource *new- descriptor of the resource to request
Description
This is a device-managed version of request_resource(). There is usually
no need to release resources requested by this function explicitly since
that will be taken care of when the device is unbound from its driver.
If for some reason the resource needs to be released explicitly, because
of ordering issues for example, drivers must call devm_release_resource()
rather than the regular release_resource().
When a conflict is detected between any existing resources and the newly requested resource, an error message will be printed.
Returns 0 on success or a negative error code on failure.
-
void
devm_release_resource(struct device *dev, struct resource *new)¶ release a previously requested resource
Parameters
struct device *dev- device for which to release the resource
struct resource *new- descriptor of the resource to release
Description
Releases a resource previously requested using devm_request_resource().
-
struct resource *
devm_request_free_mem_region(struct device *dev, struct resource *base, unsigned long size)¶ find free region for device private memory
Parameters
struct device *dev- device struct to bind the resource to
struct resource *base- resource tree to look in
unsigned long size- size in bytes of the device memory to add
Description
This function tries to find an empty range of physical address big enough to contain the new resource, so that it can later be hotplugged as ZONE_DEVICE memory, which in turn allocates struct pages.
MTRR Handling¶
-
int
arch_phys_wc_add(unsigned long base, unsigned long size)¶ add a WC MTRR and handle errors if PAT is unavailable
Parameters
unsigned long base- Physical base address
unsigned long size- Size of region
Description
If PAT is available, this does nothing. If PAT is unavailable, it attempts to add a WC MTRR covering size bytes starting at base and logs an error if this fails.
The called should provide a power of two size on an equivalent power of two boundary.
Drivers must store the return value to pass to mtrr_del_wc_if_needed, but drivers should not try to interpret that return value.
Security Framework¶
-
int
security_init(void)¶ initializes the security framework
Parameters
void- no arguments
Description
This should be called early in the kernel initialization sequence.
-
void
security_add_hooks(struct security_hook_list *hooks, int count, char *lsm)¶ Add a modules hooks to the hook lists.
Parameters
struct security_hook_list *hooks- the hooks to add
int count- the number of hooks to add
char *lsm- the name of the security module
Description
Each LSM has to register its hooks with the infrastructure.
-
int
lsm_cred_alloc(struct cred *cred, gfp_t gfp)¶ allocate a composite cred blob
Parameters
struct cred *cred- the cred that needs a blob
gfp_t gfp- allocation type
Description
Allocate the cred blob for all the modules
Returns 0, or -ENOMEM if memory can’t be allocated.
-
void
lsm_early_cred(struct cred *cred)¶ during initialization allocate a composite cred blob
Parameters
struct cred *cred- the cred that needs a blob
Description
Allocate the cred blob for all the modules
-
int
lsm_file_alloc(struct file *file)¶ allocate a composite file blob
Parameters
struct file *file- the file that needs a blob
Description
Allocate the file blob for all the modules
Returns 0, or -ENOMEM if memory can’t be allocated.
-
int
lsm_inode_alloc(struct inode *inode)¶ allocate a composite inode blob
Parameters
struct inode *inode- the inode that needs a blob
Description
Allocate the inode blob for all the modules
Returns 0, or -ENOMEM if memory can’t be allocated.
-
int
lsm_task_alloc(struct task_struct *task)¶ allocate a composite task blob
Parameters
struct task_struct *task- the task that needs a blob
Description
Allocate the task blob for all the modules
Returns 0, or -ENOMEM if memory can’t be allocated.
-
int
lsm_ipc_alloc(struct kern_ipc_perm *kip)¶ allocate a composite ipc blob
Parameters
struct kern_ipc_perm *kip- the ipc that needs a blob
Description
Allocate the ipc blob for all the modules
Returns 0, or -ENOMEM if memory can’t be allocated.
-
int
lsm_msg_msg_alloc(struct msg_msg *mp)¶ allocate a composite msg_msg blob
Parameters
struct msg_msg *mp- the msg_msg that needs a blob
Description
Allocate the ipc blob for all the modules
Returns 0, or -ENOMEM if memory can’t be allocated.
-
void
lsm_early_task(struct task_struct *task)¶ during initialization allocate a composite task blob
Parameters
struct task_struct *task- the task that needs a blob
Description
Allocate the task blob for all the modules
-
struct dentry *
securityfs_create_file(const char *name, umode_t mode, struct dentry *parent, void *data, const struct file_operations *fops)¶ create a file in the securityfs filesystem
Parameters
const char *name- a pointer to a string containing the name of the file to create.
umode_t mode- the permission that the file should have
struct dentry *parent- a pointer to the parent dentry for this file. This should be a
directory dentry if set. If this parameter is
NULL, then the file will be created in the root of the securityfs filesystem. void *data- a pointer to something that the caller will want to get to later on. The inode.i_private pointer will point to this value on the open() call.
const struct file_operations *fops- a pointer to a struct file_operations that should be used for this file.
Description
This function creates a file in securityfs with the given name.
This function returns a pointer to a dentry if it succeeds. This
pointer must be passed to the securityfs_remove() function when the file is
to be removed (no automatic cleanup happens if your module is unloaded,
you are responsible here). If an error occurs, the function will return
the error value (via ERR_PTR).
If securityfs is not enabled in the kernel, the value -ENODEV is
returned.
-
struct dentry *
securityfs_create_dir(const char *name, struct dentry *parent)¶ create a directory in the securityfs filesystem
Parameters
const char *name- a pointer to a string containing the name of the directory to create.
struct dentry *parent- a pointer to the parent dentry for this file. This should be a
directory dentry if set. If this parameter is
NULL, then the directory will be created in the root of the securityfs filesystem.
Description
This function creates a directory in securityfs with the given name.
This function returns a pointer to a dentry if it succeeds. This
pointer must be passed to the securityfs_remove() function when the file is
to be removed (no automatic cleanup happens if your module is unloaded,
you are responsible here). If an error occurs, the function will return
the error value (via ERR_PTR).
If securityfs is not enabled in the kernel, the value -ENODEV is
returned.
-
struct dentry *
securityfs_create_symlink(const char *name, struct dentry *parent, const char *target, const struct inode_operations *iops)¶ create a symlink in the securityfs filesystem
Parameters
const char *name- a pointer to a string containing the name of the symlink to create.
struct dentry *parent- a pointer to the parent dentry for the symlink. This should be a
directory dentry if set. If this parameter is
NULL, then the directory will be created in the root of the securityfs filesystem. const char *target- a pointer to a string containing the name of the symlink’s target.
If this parameter is
NULL, then the iops parameter needs to be setup to handle .readlink and .get_link inode_operations. const struct inode_operations *iops- a pointer to the struct inode_operations to use for the symlink. If
this parameter is
NULL, then the default simple_symlink_inode operations will be used.
Description
This function creates a symlink in securityfs with the given name.
This function returns a pointer to a dentry if it succeeds. This
pointer must be passed to the securityfs_remove() function when the file is
to be removed (no automatic cleanup happens if your module is unloaded,
you are responsible here). If an error occurs, the function will return
the error value (via ERR_PTR).
If securityfs is not enabled in the kernel, the value -ENODEV is
returned.
-
void
securityfs_remove(struct dentry *dentry)¶ removes a file or directory from the securityfs filesystem
Parameters
struct dentry *dentry- a pointer to a the dentry of the file or directory to be removed.
Description
This function removes a file or directory in securityfs that was previously
created with a call to another securityfs function (like
securityfs_create_file() or variants thereof.)
This function is required to be called in order for the file to be removed. No automatic cleanup of files will happen when a module is removed; you are responsible here.
Audit Interfaces¶
-
struct audit_buffer *
audit_log_start(struct audit_context *ctx, gfp_t gfp_mask, int type)¶ obtain an audit buffer
Parameters
struct audit_context *ctx- audit_context (may be NULL)
gfp_t gfp_mask- type of allocation
int type- audit message type
Description
Returns audit_buffer pointer on success or NULL on error.
Obtain an audit buffer. This routine does locking to obtain the audit buffer, but then no locking is required for calls to audit_log_*format. If the task (ctx) is a task that is currently in a syscall, then the syscall is marked as auditable and an audit record will be written at syscall exit. If there is no associated task, then task context (ctx) should be NULL.
-
void
audit_log_format(struct audit_buffer *ab, const char *fmt, ...)¶ format a message into the audit buffer.
Parameters
struct audit_buffer *ab- audit_buffer
const char *fmt- format string
...- optional parameters matching fmt string
Description
All the work is done in audit_log_vformat.
-
void
audit_log_end(struct audit_buffer *ab)¶ end one audit record
Parameters
struct audit_buffer *ab- the audit_buffer
Description
We can not do a netlink send inside an irq context because it blocks (last arg, flags, is not set to MSG_DONTWAIT), so the audit buffer is placed on a queue and a tasklet is scheduled to remove them from the queue outside the irq context. May be called in any context.
-
void
audit_log(struct audit_context *ctx, gfp_t gfp_mask, int type, const char *fmt, ...)¶ Log an audit record
Parameters
struct audit_context *ctx- audit context
gfp_t gfp_mask- type of allocation
int type- audit message type
const char *fmt- format string to use
...- variable parameters matching the format string
Description
This is a convenience function that calls audit_log_start, audit_log_vformat, and audit_log_end. It may be called in any context.
-
int
audit_alloc(struct task_struct *tsk)¶ allocate an audit context block for a task
Parameters
struct task_struct *tsk- task
Description
Filter on the task information and allocate a per-task audit context if necessary. Doing so turns on system call auditing for the specified task. This is called from copy_process, so no lock is needed.
-
void
__audit_free(struct task_struct *tsk)¶ free a per-task audit context
Parameters
struct task_struct *tsk- task whose audit context block to free
Description
Called from copy_process and do_exit
-
void
__audit_syscall_entry(int major, unsigned long a1, unsigned long a2, unsigned long a3, unsigned long a4)¶ fill in an audit record at syscall entry
Parameters
int major- major syscall type (function)
unsigned long a1- additional syscall register 1
unsigned long a2- additional syscall register 2
unsigned long a3- additional syscall register 3
unsigned long a4- additional syscall register 4
Description
Fill in audit context at syscall entry. This only happens if the audit context was created when the task was created and the state or filters demand the audit context be built. If the state from the per-task filter or from the per-syscall filter is AUDIT_RECORD_CONTEXT, then the record will be written at syscall exit time (otherwise, it will only be written if another part of the kernel requests that it be written).
-
void
__audit_syscall_exit(int success, long return_code)¶ deallocate audit context after a system call
Parameters
int success- success value of the syscall
long return_code- return value of the syscall
Description
Tear down after system call. If the audit context has been marked as auditable (either because of the AUDIT_RECORD_CONTEXT state from filtering, or because some other part of the kernel wrote an audit message), then write out the syscall information. In call cases, free the names stored from getname().
-
struct filename *
__audit_reusename(const __user char *uptr)¶ fill out filename with info from existing entry
Parameters
const __user char *uptr- userland ptr to pathname
Description
Search the audit_names list for the current audit context. If there is an existing entry with a matching “uptr” then return the filename associated with that audit_name. If not, return NULL.
-
void
__audit_getname(struct filename *name)¶ add a name to the list
Parameters
struct filename *name- name to add
Description
Add a name to the list of audit names for this context. Called from fs/namei.c:getname().
-
void
__audit_inode(struct filename *name, const struct dentry *dentry, unsigned int flags)¶ store the inode and device from a lookup
Parameters
struct filename *name- name being audited
const struct dentry *dentry- dentry being audited
unsigned int flags- attributes for this particular entry
-
int
auditsc_get_stamp(struct audit_context *ctx, struct timespec64 *t, unsigned int *serial)¶ get local copies of audit_context values
Parameters
struct audit_context *ctx- audit_context for the task
struct timespec64 *t- timespec64 to store time recorded in the audit_context
unsigned int *serial- serial value that is recorded in the audit_context
Description
Also sets the context as auditable.
-
void
__audit_mq_open(int oflag, umode_t mode, struct mq_attr *attr)¶ record audit data for a POSIX MQ open
Parameters
int oflag- open flag
umode_t mode- mode bits
struct mq_attr *attr- queue attributes
-
void
__audit_mq_sendrecv(mqd_t mqdes, size_t msg_len, unsigned int msg_prio, const struct timespec64 *abs_timeout)¶ record audit data for a POSIX MQ timed send/receive
Parameters
mqd_t mqdes- MQ descriptor
size_t msg_len- Message length
unsigned int msg_prio- Message priority
const struct timespec64 *abs_timeout- Message timeout in absolute time
-
void
__audit_mq_notify(mqd_t mqdes, const struct sigevent *notification)¶ record audit data for a POSIX MQ notify
Parameters
mqd_t mqdes- MQ descriptor
const struct sigevent *notification- Notification event
-
void
__audit_mq_getsetattr(mqd_t mqdes, struct mq_attr *mqstat)¶ record audit data for a POSIX MQ get/set attribute
Parameters
mqd_t mqdes- MQ descriptor
struct mq_attr *mqstat- MQ flags
-
void
__audit_ipc_obj(struct kern_ipc_perm *ipcp)¶ record audit data for ipc object
Parameters
struct kern_ipc_perm *ipcp- ipc permissions
-
void
__audit_ipc_set_perm(unsigned long qbytes, uid_t uid, gid_t gid, umode_t mode)¶ record audit data for new ipc permissions
Parameters
unsigned long qbytes- msgq bytes
uid_t uid- msgq user id
gid_t gid- msgq group id
umode_t mode- msgq mode (permissions)
Description
Called only after audit_ipc_obj().
-
int
__audit_socketcall(int nargs, unsigned long *args)¶ record audit data for sys_socketcall
Parameters
int nargs- number of args, which should not be more than AUDITSC_ARGS.
unsigned long *args- args array
-
void
__audit_fd_pair(int fd1, int fd2)¶ record audit data for pipe and socketpair
Parameters
int fd1- the first file descriptor
int fd2- the second file descriptor
-
int
__audit_sockaddr(int len, void *a)¶ record audit data for sys_bind, sys_connect, sys_sendto
Parameters
int len- data length in user space
void *a- data address in kernel space
Description
Returns 0 for success or NULL context or < 0 on error.
-
int
audit_signal_info_syscall(struct task_struct *t)¶ record signal info for syscalls
Parameters
struct task_struct *t- task being signaled
Description
If the audit subsystem is being terminated, record the task (pid) and uid that is doing that.
-
int
__audit_log_bprm_fcaps(struct linux_binprm *bprm, const struct cred *new, const struct cred *old)¶ store information about a loading bprm and relevant fcaps
Parameters
struct linux_binprm *bprm- pointer to the bprm being processed
const struct cred *new- the proposed new credentials
const struct cred *old- the old credentials
Description
Simply check if the proc already has the caps given by the file and if not store the priv escalation info for later auditing at the end of the syscall
-Eric
-
void
__audit_log_capset(const struct cred *new, const struct cred *old)¶ store information about the arguments to the capset syscall
Parameters
const struct cred *new- the new credentials
const struct cred *old- the old (current) credentials
Description
Record the arguments userspace sent to sys_capset for later printing by the audit system if applicable
-
void
audit_core_dumps(long signr)¶ record information about processes that end abnormally
Parameters
long signr- signal value
Description
If a process ends with a core dump, something fishy is going on and we should record the event for investigation.
-
void
audit_seccomp(unsigned long syscall, long signr, int code)¶ record information about a seccomp action
Parameters
unsigned long syscall- syscall number
long signr- signal value
int code- the seccomp action
Description
Record the information associated with a seccomp action. Event filtering for seccomp actions that are not to be logged is done in seccomp_log(). Therefore, this function forces auditing independent of the audit_enabled and dummy context state because seccomp actions should be logged even when audit is not in use.
-
int
audit_rule_change(int type, int seq, void *data, size_t datasz)¶ apply all rules to the specified message type
Parameters
int type- audit message type
int seq- netlink audit message sequence (serial) number
void *data- payload data
size_t datasz- size of payload data
Parameters
struct sk_buff *request_skb- skb of request we are replying to (used to target the reply)
int seq- netlink audit message sequence (serial) number
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int
parent_len(const char *path)¶ find the length of the parent portion of a pathname
Parameters
const char *path- pathname of which to determine length
-
int
audit_compare_dname_path(const struct qstr *dname, const char *path, int parentlen)¶ compare given dentry name with last component in given path. Return of 0 indicates a match.
Parameters
const struct qstr *dname- dentry name that we’re comparing
const char *path- full pathname that we’re comparing
int parentlen- length of the parent if known. Passing in AUDIT_NAME_FULL here indicates that we must compute this value.
Accounting Framework¶
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long
sys_acct(const char __user * name)¶ enable/disable process accounting
Parameters
const char __user * name- file name for accounting records or NULL to shutdown accounting
Description
sys_acct() is the only system call needed to implement process
accounting. It takes the name of the file where accounting records
should be written. If the filename is NULL, accounting will be
shutdown.
Return
0 for success or negative errno values for failure.
-
void
acct_collect(long exitcode, int group_dead)¶ collect accounting information into pacct_struct
Parameters
long exitcode- task exit code
int group_dead- not 0, if this thread is the last one in the process.
-
void
acct_process(void)¶ handles process accounting for an exiting task
Parameters
void- no arguments
Block Devices¶
-
void
blk_queue_flag_set(unsigned int flag, struct request_queue *q)¶ atomically set a queue flag
Parameters
unsigned int flag- flag to be set
struct request_queue *q- request queue
-
void
blk_queue_flag_clear(unsigned int flag, struct request_queue *q)¶ atomically clear a queue flag
Parameters
unsigned int flag- flag to be cleared
struct request_queue *q- request queue
-
bool
blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q)¶ atomically test and set a queue flag
Parameters
unsigned int flag- flag to be set
struct request_queue *q- request queue
Description
Returns the previous value of flag - 0 if the flag was not set and 1 if the flag was already set.
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const char *
blk_op_str(unsigned int op)¶ Return string XXX in the REQ_OP_XXX.
Parameters
unsigned int op- REQ_OP_XXX.
Description
Centralize block layer function to convert REQ_OP_XXX into string format. Useful in the debugging and tracing bio or request. For invalid REQ_OP_XXX it returns string “UNKNOWN”.
-
void
blk_sync_queue(struct request_queue *q)¶ cancel any pending callbacks on a queue
Parameters
struct request_queue *q- the queue
Description
The block layer may perform asynchronous callback activity on a queue, such as calling the unplug function after a timeout. A block device may call blk_sync_queue to ensure that any such activity is cancelled, thus allowing it to release resources that the callbacks might use. The caller must already have made sure that its ->submit_bio will not re-add plugging prior to calling this function.
This function does not cancel any asynchronous activity arising out of elevator or throttling code. That would require elevator_exit() and blkcg_exit_queue() to be called with queue lock initialized.
-
void
blk_set_pm_only(struct request_queue *q)¶ increment pm_only counter
Parameters
struct request_queue *q- request queue pointer
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void
blk_put_queue(struct request_queue *q)¶ decrement the request_queue refcount
Parameters
struct request_queue *q- the request_queue structure to decrement the refcount for
Description
Decrements the refcount of the request_queue kobject. When this reaches 0
we’ll have blk_release_queue() called.
Context
Any context, but the last reference must not be dropped from atomic context.
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void
blk_cleanup_queue(struct request_queue *q)¶ shutdown a request queue
Parameters
struct request_queue *q- request queue to shutdown
Description
Mark q DYING, drain all pending requests, mark q DEAD, destroy and put it. All future requests will be failed immediately with -ENODEV.
Context
can sleep
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bool
blk_get_queue(struct request_queue *q)¶ increment the request_queue refcount
Parameters
struct request_queue *q- the request_queue structure to increment the refcount for
Description
Increment the refcount of the request_queue kobject.
Context
Any context.
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struct request *
blk_get_request(struct request_queue *q, unsigned int op, blk_mq_req_flags_t flags)¶ allocate a request
Parameters
struct request_queue *q- request queue to allocate a request for
unsigned int op- operation (REQ_OP_*) and REQ_* flags, e.g. REQ_SYNC.
blk_mq_req_flags_t flags- BLK_MQ_REQ_* flags, e.g. BLK_MQ_REQ_NOWAIT.
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blk_qc_t
submit_bio_noacct(struct bio *bio)¶ re-submit a bio to the block device layer for I/O
Parameters
struct bio *bio- The bio describing the location in memory and on the device.
Description
This is a version of submit_bio() that shall only be used for I/O that is
resubmitted to lower level drivers by stacking block drivers. All file
systems and other upper level users of the block layer should use
submit_bio() instead.
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blk_qc_t
submit_bio(struct bio *bio)¶ submit a bio to the block device layer for I/O
Parameters
struct bio *bio- The
struct biowhich describes the I/O
Description
submit_bio() is used to submit I/O requests to block devices. It is passed a
fully set up struct bio that describes the I/O that needs to be done. The
bio will be send to the device described by the bi_disk and bi_partno fields.
The success/failure status of the request, along with notification of completion, is delivered asynchronously through the ->bi_end_io() callback in bio. The bio must NOT be touched by thecaller until ->bi_end_io() has been called.
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blk_status_t
blk_insert_cloned_request(struct request_queue *q, struct request *rq)¶ Helper for stacking drivers to submit a request
Parameters
struct request_queue *q- the queue to submit the request
struct request *rq- the request being queued
-
unsigned int
blk_rq_err_bytes(const struct request *rq)¶ determine number of bytes till the next failure boundary
Parameters
const struct request *rq- request to examine
Description
A request could be merge of IOs which require different failure handling. This function determines the number of bytes which can be failed from the beginning of the request without crossing into area which need to be retried further.
Return
The number of bytes to fail.
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bool
blk_update_request(struct request *req, blk_status_t error, unsigned int nr_bytes)¶ Special helper function for request stacking drivers
Parameters
struct request *req- the request being processed
blk_status_t error- block status code
unsigned int nr_bytes- number of bytes to complete req
Description
Ends I/O on a number of bytes attached to req, but doesn’t complete the request structure even if req doesn’t have leftover. If req has leftover, sets it up for the next range of segments.
This special helper function is only for request stacking drivers (e.g. request-based dm) so that they can handle partial completion. Actual device drivers should use blk_mq_end_request instead.
Passing the result of blk_rq_bytes() as nr_bytes guarantees
falsereturn from this function.
Note
The RQF_SPECIAL_PAYLOAD flag is ignored on purpose in both blk_rq_bytes() and inblk_update_request().
Return
false- this request doesn’t have any more datatrue- this request has more data
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void
rq_flush_dcache_pages(struct request *rq)¶ Helper function to flush all pages in a request
Parameters
struct request *rq- the request to be flushed
Description
Flush all pages in rq.
-
int
blk_lld_busy(struct request_queue *q)¶ Check if underlying low-level drivers of a device are busy
Parameters
struct request_queue *q- the queue of the device being checked
Description
Check if underlying low-level drivers of a device are busy. If the drivers want to export their busy state, they must set own exporting function using blk_queue_lld_busy() first.
Basically, this function is used only by request stacking drivers to stop dispatching requests to underlying devices when underlying devices are busy. This behavior helps more I/O merging on the queue of the request stacking driver and prevents I/O throughput regression on burst I/O load.
Return
0 - Not busy (The request stacking driver should dispatch request) 1 - Busy (The request stacking driver should stop dispatching request)
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void
blk_rq_unprep_clone(struct request *rq)¶ Helper function to free all bios in a cloned request
Parameters
struct request *rq- the clone request to be cleaned up
Description
Free all bios in rq for a cloned request.
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int
blk_rq_prep_clone(struct request *rq, struct request *rq_src, struct bio_set *bs, gfp_t gfp_mask, int (*bio_ctr)(struct bio *, struct bio *, void *), void *data)¶ Helper function to setup clone request
Parameters
struct request *rq- the request to be setup
struct request *rq_src- original request to be cloned
struct bio_set *bs- bio_set that bios for clone are allocated from
gfp_t gfp_mask- memory allocation mask for bio
int (*bio_ctr)(struct bio *, struct bio *, void *)- setup function to be called for each clone bio.
Returns
0for success, non0for failure. void *data- private data to be passed to bio_ctr
Description
Clones bios in rq_src to rq, and copies attributes of rq_src to rq. Also, pages which the original bios are pointing to are not copied and the cloned bios just point same pages. So cloned bios must be completed before original bios, which means the caller must complete rq before rq_src.
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void
blk_start_plug(struct blk_plug *plug)¶ initialize blk_plug and track it inside the task_struct
Parameters
struct blk_plug *plug- The
struct blk_plugthat needs to be initialized
Description
blk_start_plug()indicates to the block layer an intent by the caller to submit multiple I/O requests in a batch. The block layer may use this hint to defer submitting I/Os from the caller untilblk_finish_plug()is called. However, the block layer may choose to submit requests before a call toblk_finish_plug()if the number of queued I/Os exceedsBLK_MAX_REQUEST_COUNT, or if the size of the I/O is larger thanBLK_PLUG_FLUSH_SIZE. The queued I/Os may also be submitted early if the task schedules (see below).Tracking blk_plug inside the task_struct will help with auto-flushing the pending I/O should the task end up blocking between
blk_start_plug()andblk_finish_plug(). This is important from a performance perspective, but also ensures that we don’t deadlock. For instance, if the task is blocking for a memory allocation, memory reclaim could end up wanting to free a page belonging to that request that is currently residing in our private plug. By flushing the pending I/O when the process goes to sleep, we avoid this kind of deadlock.
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void
blk_finish_plug(struct blk_plug *plug)¶ mark the end of a batch of submitted I/O
Parameters
struct blk_plug *plug- The
struct blk_plugpassed toblk_start_plug()
Description
Indicate that a batch of I/O submissions is complete. This function
must be paired with an initial call to blk_start_plug(). The intent
is to allow the block layer to optimize I/O submission. See the
documentation for blk_start_plug() for more information.
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int
blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)¶ try to increase q->q_usage_counter
Parameters
struct request_queue *q- request queue pointer
blk_mq_req_flags_t flags- BLK_MQ_REQ_NOWAIT and/or BLK_MQ_REQ_PM
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blk_status_t
blk_cloned_rq_check_limits(struct request_queue *q, struct request *rq)¶ Helper function to check a cloned request for the new queue limits
Parameters
struct request_queue *q- the queue
struct request *rq- the request being checked
Description
rq may have been made based on weaker limitations of upper-level queues in request stacking drivers, and it may violate the limitation of q. Since the block layer and the underlying device driver trust rq after it is inserted to q, it should be checked against q before the insertion using this generic function.
Request stacking drivers like request-based dm may change the queue limits when retrying requests on other queues. Those requests need to be checked against the new queue limits again during dispatch.
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int
blk_rq_map_user_iov(struct request_queue *q, struct request *rq, struct rq_map_data *map_data, const struct iov_iter *iter, gfp_t gfp_mask)¶ map user data to a request, for passthrough requests
Parameters
struct request_queue *q- request queue where request should be inserted
struct request *rq- request to map data to
struct rq_map_data *map_data- pointer to the rq_map_data holding pages (if necessary)
const struct iov_iter *iter- iovec iterator
gfp_t gfp_mask- memory allocation flags
Description
Data will be mapped directly for zero copy I/O, if possible. Otherwise a kernel bounce buffer is used.
A matching
blk_rq_unmap_user()must be issued at the end of I/O, while still in process context.
Note
- The mapped bio may need to be bounced through blk_queue_bounce()
- before being submitted to the device, as pages mapped may be out of
reach. It’s the callers responsibility to make sure this happens. The
original bio must be passed back in to
blk_rq_unmap_user()for proper unmapping.
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int
blk_rq_unmap_user(struct bio *bio)¶ unmap a request with user data
Parameters
struct bio *bio- start of bio list
Description
Unmap a rq previously mapped by blk_rq_map_user(). The caller must supply the original rq->bio from the blk_rq_map_user() return, since the I/O completion may have changed rq->bio.
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int
blk_rq_map_kern(struct request_queue *q, struct request *rq, void *kbuf, unsigned int len, gfp_t gfp_mask)¶ map kernel data to a request, for passthrough requests
Parameters
struct request_queue *q- request queue where request should be inserted
struct request *rq- request to fill
void *kbuf- the kernel buffer
unsigned int len- length of user data
gfp_t gfp_mask- memory allocation flags
Description
Data will be mapped directly if possible. Otherwise a bounce buffer is used. Can be called multiple times to append multiple buffers.
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void
blk_release_queue(struct kobject *kobj)¶ releases all allocated resources of the request_queue
Parameters
struct kobject *kobj- pointer to a kobject, whose container is a request_queue
Description
This function releases all allocated resources of the request queue.
The struct request_queue refcount is incremented with blk_get_queue() and
decremented with blk_put_queue(). Once the refcount reaches 0 this function
is called.
For drivers that have a request_queue on a gendisk and added with
__device_add_disk() the refcount to request_queue will reach 0 with
the last put_disk() called by the driver. For drivers which don’t use
__device_add_disk() this happens with blk_cleanup_queue().
Drivers exist which depend on the release of the request_queue to be synchronous, it should not be deferred.
Context
can sleep
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void
blk_unregister_queue(struct gendisk *disk)¶ counterpart of blk_register_queue()
Parameters
struct gendisk *disk- Disk of which the request queue should be unregistered from sysfs.
Note
the caller is responsible for guaranteeing that this function is called after blk_register_queue() has finished.
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void
blk_set_default_limits(struct queue_limits *lim)¶ reset limits to default values
Parameters
struct queue_limits *lim- the queue_limits structure to reset
Description
Returns a queue_limit struct to its default state.
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void
blk_set_stacking_limits(struct queue_limits *lim)¶ set default limits for stacking devices
Parameters
struct queue_limits *lim- the queue_limits structure to reset
Description
Returns a queue_limit struct to its default state. Should be used by stacking drivers like DM that have no internal limits.
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void
blk_queue_bounce_limit(struct request_queue *q, u64 max_addr)¶ set bounce buffer limit for queue
Parameters
struct request_queue *q- the request queue for the device
u64 max_addr- the maximum address the device can handle
Description
Different hardware can have different requirements as to what pages it can do I/O directly to. A low level driver can call blk_queue_bounce_limit to have lower memory pages allocated as bounce buffers for doing I/O to pages residing above max_addr.
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void
blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)¶ set max sectors for a request for this queue
Parameters
struct request_queue *q- the request queue for the device
unsigned int max_hw_sectors- max hardware sectors in the usual 512b unit
Description
Enables a low level driver to set a hard upper limit, max_hw_sectors, on the size of requests. max_hw_sectors is set by the device driver based upon the capabilities of the I/O controller.
max_dev_sectors is a hard limit imposed by the storage device for READ/WRITE requests. It is set by the disk driver.
max_sectors is a soft limit imposed by the block layer for filesystem type requests. This value can be overridden on a per-device basis in /sys/block/<device>/queue/max_sectors_kb. The soft limit can not exceed max_hw_sectors.
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void
blk_queue_chunk_sectors(struct request_queue *q, unsigned int chunk_sectors)¶ set size of the chunk for this queue
Parameters
struct request_queue *q- the request queue for the device
unsigned int chunk_sectors- chunk sectors in the usual 512b unit
Description
If a driver doesn’t want IOs to cross a given chunk size, it can set this limit and prevent merging across chunks. Note that the block layer must accept a page worth of data at any offset. So if the crossing of chunks is a hard limitation in the driver, it must still be prepared to split single page bios.
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void
blk_queue_max_discard_sectors(struct request_queue *q, unsigned int max_discard_sectors)¶ set max sectors for a single discard
Parameters
struct request_queue *q- the request queue for the device
unsigned int max_discard_sectors- maximum number of sectors to discard
-
void
blk_queue_max_write_same_sectors(struct request_queue *q, unsigned int max_write_same_sectors)¶ set max sectors for a single write same
Parameters
struct request_queue *q- the request queue for the device
unsigned int max_write_same_sectors- maximum number of sectors to write per command
-
void
blk_queue_max_write_zeroes_sectors(struct request_queue *q, unsigned int max_write_zeroes_sectors)¶ set max sectors for a single write zeroes
Parameters
struct request_queue *q- the request queue for the device
unsigned int max_write_zeroes_sectors- maximum number of sectors to write per command
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void
blk_queue_max_zone_append_sectors(struct request_queue *q, unsigned int max_zone_append_sectors)¶ set max sectors for a single zone append
Parameters
struct request_queue *q- the request queue for the device
unsigned int max_zone_append_sectors- maximum number of sectors to write per command
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void
blk_queue_max_segments(struct request_queue *q, unsigned short max_segments)¶ set max hw segments for a request for this queue
Parameters
struct request_queue *q- the request queue for the device
unsigned short max_segments- max number of segments
Description
Enables a low level driver to set an upper limit on the number of hw data segments in a request.
-
void
blk_queue_max_discard_segments(struct request_queue *q, unsigned short max_segments)¶ set max segments for discard requests
Parameters
struct request_queue *q- the request queue for the device
unsigned short max_segments- max number of segments
Description
Enables a low level driver to set an upper limit on the number of segments in a discard request.
-
void
blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)¶ set max segment size for blk_rq_map_sg
Parameters
struct request_queue *q- the request queue for the device
unsigned int max_size- max size of segment in bytes
Description
Enables a low level driver to set an upper limit on the size of a coalesced segment
-
void
blk_queue_logical_block_size(struct request_queue *q, unsigned int size)¶ set logical block size for the queue
Parameters
struct request_queue *q- the request queue for the device
unsigned int size- the logical block size, in bytes
Description
This should be set to the lowest possible block size that the storage device can address. The default of 512 covers most hardware.
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void
blk_queue_physical_block_size(struct request_queue *q, unsigned int size)¶ set physical block size for the queue
Parameters
struct request_queue *q- the request queue for the device
unsigned int size- the physical block size, in bytes
Description
This should be set to the lowest possible sector size that the hardware can operate on without reverting to read-modify-write operations.
-
void
blk_queue_alignment_offset(struct request_queue *q, unsigned int offset)¶ set physical block alignment offset
Parameters
struct request_queue *q- the request queue for the device
unsigned int offset- alignment offset in bytes
Description
Some devices are naturally misaligned to compensate for things like the legacy DOS partition table 63-sector offset. Low-level drivers should call this function for devices whose first sector is not naturally aligned.
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void
blk_limits_io_min(struct queue_limits *limits, unsigned int min)¶ set minimum request size for a device
Parameters
struct queue_limits *limits- the queue limits
unsigned int min- smallest I/O size in bytes
Description
Some devices have an internal block size bigger than the reported hardware sector size. This function can be used to signal the smallest I/O the device can perform without incurring a performance penalty.
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void
blk_queue_io_min(struct request_queue *q, unsigned int min)¶ set minimum request size for the queue
Parameters
struct request_queue *q- the request queue for the device
unsigned int min- smallest I/O size in bytes
Description
Storage devices may report a granularity or preferred minimum I/O size which is the smallest request the device can perform without incurring a performance penalty. For disk drives this is often the physical block size. For RAID arrays it is often the stripe chunk size. A properly aligned multiple of minimum_io_size is the preferred request size for workloads where a high number of I/O operations is desired.
-
void
blk_limits_io_opt(struct queue_limits *limits, unsigned int opt)¶ set optimal request size for a device
Parameters
struct queue_limits *limits- the queue limits
unsigned int opt- smallest I/O size in bytes
Description
Storage devices may report an optimal I/O size, which is the device’s preferred unit for sustained I/O. This is rarely reported for disk drives. For RAID arrays it is usually the stripe width or the internal track size. A properly aligned multiple of optimal_io_size is the preferred request size for workloads where sustained throughput is desired.
-
void
blk_queue_io_opt(struct request_queue *q, unsigned int opt)¶ set optimal request size for the queue
Parameters
struct request_queue *q- the request queue for the device
unsigned int opt- optimal request size in bytes
Description
Storage devices may report an optimal I/O size, which is the device’s preferred unit for sustained I/O. This is rarely reported for disk drives. For RAID arrays it is usually the stripe width or the internal track size. A properly aligned multiple of optimal_io_size is the preferred request size for workloads where sustained throughput is desired.
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int
blk_stack_limits(struct queue_limits *t, struct queue_limits *b, sector_t start)¶ adjust queue_limits for stacked devices
Parameters
struct queue_limits *t- the stacking driver limits (top device)
struct queue_limits *b- the underlying queue limits (bottom, component device)
sector_t start- first data sector within component device
Description
This function is used by stacking drivers like MD and DM to ensure that all component devices have compatible block sizes and alignments. The stacking driver must provide a queue_limits struct (top) and then iteratively call the stacking function for all component (bottom) devices. The stacking function will attempt to combine the values and ensure proper alignment.
Returns 0 if the top and bottom queue_limits are compatible. The top device’s block sizes and alignment offsets may be adjusted to ensure alignment with the bottom device. If no compatible sizes and alignments exist, -1 is returned and the resulting top queue_limits will have the misaligned flag set to indicate that the alignment_offset is undefined.
-
void
disk_stack_limits(struct gendisk *disk, struct block_device *bdev, sector_t offset)¶ adjust queue limits for stacked drivers
Parameters
struct gendisk *disk- MD/DM gendisk (top)
struct block_device *bdev- the underlying block device (bottom)
sector_t offset- offset to beginning of data within component device
Description
Merges the limits for a top level gendisk and a bottom level block_device.
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void
blk_queue_update_dma_pad(struct request_queue *q, unsigned int mask)¶ update pad mask
Parameters
struct request_queue *q- the request queue for the device
unsigned int mask- pad mask
Description
Update dma pad mask.
Appending pad buffer to a request modifies the last entry of a scatter list such that it includes the pad buffer.
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void
blk_queue_segment_boundary(struct request_queue *q, unsigned long mask)¶ set boundary rules for segment merging
Parameters
struct request_queue *q- the request queue for the device
unsigned long mask- the memory boundary mask
-
void
blk_queue_virt_boundary(struct request_queue *q, unsigned long mask)¶ set boundary rules for bio merging
Parameters
struct request_queue *q- the request queue for the device
unsigned long mask- the memory boundary mask
-
void
blk_queue_dma_alignment(struct request_queue *q, int mask)¶ set dma length and memory alignment
Parameters
struct request_queue *q- the request queue for the device
int mask- alignment mask
Description
set required memory and length alignment for direct dma transactions. this is used when building direct io requests for the queue.
-
void
blk_queue_update_dma_alignment(struct request_queue *q, int mask)¶ update dma length and memory alignment
Parameters
struct request_queue *q- the request queue for the device
int mask- alignment mask
Description
update required memory and length alignment for direct dma transactions. If the requested alignment is larger than the current alignment, then the current queue alignment is updated to the new value, otherwise it is left alone. The design of this is to allow multiple objects (driver, device, transport etc) to set their respective alignments without having them interfere.
-
void
blk_set_queue_depth(struct request_queue *q, unsigned int depth)¶ tell the block layer about the device queue depth
Parameters
struct request_queue *q- the request queue for the device
unsigned int depth- queue depth
-
void
blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)¶ configure queue’s write cache
Parameters
struct request_queue *q- the request queue for the device
bool wc- write back cache on or off
bool fua- device supports FUA writes, if true
Description
Tell the block layer about the write cache of q.
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void
blk_queue_required_elevator_features(struct request_queue *q, unsigned int features)¶ Set a queue required elevator features
Parameters
struct request_queue *q- the request queue for the target device
unsigned int features- Required elevator features OR’ed together
Description
Tell the block layer that for the device controlled through q, only the only elevators that can be used are those that implement at least the set of features specified by features.
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bool
blk_queue_can_use_dma_map_merging(struct request_queue *q, struct device *dev)¶ configure queue for merging segments.
Parameters
struct request_queue *q- the request queue for the device
struct device *dev- the device pointer for dma
Description
Tell the block layer about merging the segments by dma map of q.
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void
blk_queue_set_zoned(struct gendisk *disk, enum blk_zoned_model model)¶ configure a disk queue zoned model.
Parameters
struct gendisk *disk- the gendisk of the queue to configure
enum blk_zoned_model model- the zoned model to set
Description
Set the zoned model of the request queue of disk according to model. When model is BLK_ZONED_HM (host managed), this should be called only if zoned block device support is enabled (CONFIG_BLK_DEV_ZONED option). If model specifies BLK_ZONED_HA (host aware), the effective model used depends on CONFIG_BLK_DEV_ZONED settings and on the existence of partitions on the disk.
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void
blk_execute_rq_nowait(struct request_queue *q, struct gendisk *bd_disk, struct request *rq, int at_head, rq_end_io_fn *done)¶ insert a request into queue for execution
Parameters
struct request_queue *q- queue to insert the request in
struct gendisk *bd_disk- matching gendisk
struct request *rq- request to insert
int at_head- insert request at head or tail of queue
rq_end_io_fn *done- I/O completion handler
Description
Insert a fully prepared request at the back of the I/O scheduler queue for execution. Don’t wait for completion.
Note
This function will invoke done directly if the queue is dead.
-
void
blk_execute_rq(struct request_queue *q, struct gendisk *bd_disk, struct request *rq, int at_head)¶ insert a request into queue for execution
Parameters
struct request_queue *q- queue to insert the request in
struct gendisk *bd_disk- matching gendisk
struct request *rq- request to insert
int at_head- insert request at head or tail of queue
Description
Insert a fully prepared request at the back of the I/O scheduler queue for execution and wait for completion.
-
int
blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask)¶ queue a flush
Parameters
struct block_device *bdev- blockdev to issue flush for
gfp_t gfp_mask- memory allocation flags (for bio_alloc)
Description
Issue a flush for the block device in question.
-
int
blkdev_issue_discard(struct block_device *bdev, sector_t sector, sector_t nr_sects, gfp_t gfp_mask, unsigned long flags)¶ queue a discard
Parameters
struct block_device *bdev- blockdev to issue discard for
sector_t sector- start sector
sector_t nr_sects- number of sectors to discard
gfp_t gfp_mask- memory allocation flags (for bio_alloc)
unsigned long flags- BLKDEV_DISCARD_* flags to control behaviour
Description
Issue a discard request for the sectors in question.
-
int
blkdev_issue_write_same(struct block_device *bdev, sector_t sector, sector_t nr_sects, gfp_t gfp_mask, struct page *page)¶ queue a write same operation
Parameters
struct block_device *bdev- target blockdev
sector_t sector- start sector
sector_t nr_sects- number of sectors to write
gfp_t gfp_mask- memory allocation flags (for bio_alloc)
struct page *page- page containing data
Description
Issue a write same request for the sectors in question.
-
int
__blkdev_issue_zeroout(struct block_device *bdev, sector_t sector, sector_t nr_sects, gfp_t gfp_mask, struct bio **biop, unsigned flags)¶ generate number of zero filed write bios
Parameters
struct block_device *bdev- blockdev to issue
sector_t sector- start sector
sector_t nr_sects- number of sectors to write
gfp_t gfp_mask- memory allocation flags (for bio_alloc)
struct bio **biop- pointer to anchor bio
unsigned flags- controls detailed behavior
Description
Zero-fill a block range, either using hardware offload or by explicitly writing zeroes to the device.
If a device is using logical block provisioning, the underlying space will not be released if
flagscontains BLKDEV_ZERO_NOUNMAP.If
flagscontains BLKDEV_ZERO_NOFALLBACK, the function will return -EOPNOTSUPP if no explicit hardware offload for zeroing is provided.
-
int
blkdev_issue_zeroout(struct block_device *bdev, sector_t sector, sector_t nr_sects, gfp_t gfp_mask, unsigned flags)¶ zero-fill a block range
Parameters
struct block_device *bdev- blockdev to write
sector_t sector- start sector
sector_t nr_sects- number of sectors to write
gfp_t gfp_mask- memory allocation flags (for bio_alloc)
unsigned flags- controls detailed behavior
Description
Zero-fill a block range, either using hardware offload or by explicitly writing zeroes to the device. See__blkdev_issue_zeroout()for the valid values forflags.
-
int
blk_rq_count_integrity_sg(struct request_queue *q, struct bio *bio)¶ Count number of integrity scatterlist elements
Parameters
struct request_queue *q- request queue
struct bio *bio- bio with integrity metadata attached
Description
Returns the number of elements required in a scatterlist corresponding to the integrity metadata in a bio.
-
int
blk_rq_map_integrity_sg(struct request_queue *q, struct bio *bio, struct scatterlist *sglist)¶ Map integrity metadata into a scatterlist
Parameters
struct request_queue *q- request queue
struct bio *bio- bio with integrity metadata attached
struct scatterlist *sglist- target scatterlist
Description
Map the integrity vectors in request into a
scatterlist. The scatterlist must be big enough to hold all
elements. I.e. sized using blk_rq_count_integrity_sg().
-
int
blk_integrity_compare(struct gendisk *gd1, struct gendisk *gd2)¶ Compare integrity profile of two disks
Parameters
struct gendisk *gd1- Disk to compare
struct gendisk *gd2- Disk to compare
Description
Meta-devices like DM and MD need to verify that all sub-devices use the same integrity format before advertising to upper layers that they can send/receive integrity metadata. This function can be used to check whether two gendisk devices have compatible integrity formats.
-
void
blk_integrity_register(struct gendisk *disk, struct blk_integrity *template)¶ Register a gendisk as being integrity-capable
Parameters
struct gendisk *disk- struct gendisk pointer to make integrity-aware
struct blk_integrity *template- block integrity profile to register
Description
When a device needs to advertise itself as being able to send/receive integrity metadata it must use this function to register the capability with the block layer. The template is a blk_integrity struct with values appropriate for the underlying hardware. See Data Integrity.
-
void
blk_integrity_unregister(struct gendisk *disk)¶ Unregister block integrity profile
Parameters
struct gendisk *disk- disk whose integrity profile to unregister
Description
This function unregisters the integrity capability from a block device.
-
int
blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)¶ handle the ioctls associated with tracing
Parameters
struct block_device *bdev- the block device
unsigned cmd- the ioctl cmd
char __user *arg- the argument data, if any
-
void
blk_trace_shutdown(struct request_queue *q)¶ stop and cleanup trace structures
Parameters
struct request_queue *q- the request queue associated with the device
-
void
blk_add_trace_rq(struct request *rq, int error, unsigned int nr_bytes, u32 what, u64 cgid)¶ Add a trace for a request oriented action
Parameters
struct request *rq- the source request
int error- return status to log
unsigned int nr_bytes- number of completed bytes
u32 what- the action
u64 cgid- the cgroup info
Description
Records an action against a request. Will log the bio offset + size.
-
void
blk_add_trace_bio(struct request_queue *q, struct bio *bio, u32 what, int error)¶ Add a trace for a bio oriented action
Parameters
struct request_queue *q- queue the io is for
struct bio *bio- the source bio
u32 what- the action
int error- error, if any
Description
Records an action against a bio. Will log the bio offset + size.
-
void
blk_add_trace_bio_remap(void *ignore, struct bio *bio, dev_t dev, sector_t from)¶ Add a trace for a bio-remap operation
Parameters
void *ignore- trace callback data parameter (not used)
struct bio *bio- the source bio
dev_t dev- source device
sector_t from- source sector
Description
Called after a bio is remapped to a different device and/or sector.
-
void
blk_add_trace_rq_remap(void *ignore, struct request *rq, dev_t dev, sector_t from)¶ Add a trace for a request-remap operation
Parameters
void *ignore- trace callback data parameter (not used)
struct request *rq- the source request
dev_t dev- target device
sector_t from- source sector
Description
Device mapper remaps request to other devices. Add a trace for that action.
-
struct block_device *
disk_map_sector_rcu(struct gendisk *disk, sector_t sector)¶ map sector to partition
Parameters
struct gendisk *disk- gendisk of interest
sector_t sector- sector to map
Description
Find out which partition sector maps to on disk. This is primarily used for stats accounting.
Context
RCU read locked.
Return
Found partition on success, part0 is returned if no partition matches or the matched partition is being deleted.
-
int
blk_mangle_minor(int minor)¶ scatter minor numbers apart
Parameters
int minor- minor number to mangle
Description
Scatter consecutively allocated minor number apart if MANGLE_DEVT is enabled. Mangling twice gives the original value.
Return
Mangled value.
Context
Don’t care.
-
int
blk_alloc_devt(struct block_device *bdev, dev_t *devt)¶ allocate a dev_t for a block device
Parameters
struct block_device *bdev- block device to allocate dev_t for
dev_t *devt- out parameter for resulting dev_t
Description
Allocate a dev_t for block device.
Return
0 on success, allocated dev_t is returned in *devt. -errno on failure.
Context
Might sleep.
-
void
blk_free_devt(dev_t devt)¶ free a dev_t
Parameters
dev_t devt- dev_t to free
Description
Free devt which was allocated using blk_alloc_devt().
Context
Might sleep.
-
void
__device_add_disk(struct device *parent, struct gendisk *disk, const struct attribute_group **groups, bool register_queue)¶ add disk information to kernel list
Parameters
struct device *parent- parent device for the disk
struct gendisk *disk- per-device partitioning information
const struct attribute_group **groups- Additional per-device sysfs groups
bool register_queue- register the queue if set to true
Description
This function registers the partitioning information in disk with the kernel.
FIXME: error handling
-
struct block_device *
bdget_disk(struct gendisk *disk, int partno)¶ do bdget() by gendisk and partition number
Parameters
struct gendisk *disk- gendisk of interest
int partno- partition number
Description
Find partition partno from disk, do bdget() on it.
Context
Don’t care.
Return
Resulting block_device on success, NULL on failure.
-
void
disk_replace_part_tbl(struct gendisk *disk, struct disk_part_tbl *new_ptbl)¶ replace disk->part_tbl in RCU-safe way
Parameters
struct gendisk *disk- disk to replace part_tbl for
struct disk_part_tbl *new_ptbl- new part_tbl to install
Description
Replace disk->part_tbl with new_ptbl in RCU-safe way. The original ptbl is freed using RCU callback.
LOCKING: Matching bd_mutex locked or the caller is the only user of disk.
-
int
disk_expand_part_tbl(struct gendisk *disk, int partno)¶ expand disk->part_tbl
Parameters
struct gendisk *disk- disk to expand part_tbl for
int partno- expand such that this partno can fit in
Description
Expand disk->part_tbl such that partno can fit in. disk->part_tbl uses RCU to allow unlocked dereferencing for stats and other stuff.
LOCKING: Matching bd_mutex locked or the caller is the only user of disk. Might sleep.
Return
0 on success, -errno on failure.
Parameters
struct device *dev- the device representing this disk
Description
This function releases all allocated resources of the gendisk.
Drivers which used __device_add_disk() have a gendisk with a request_queue
assigned. Since the request_queue sits on top of the gendisk for these
drivers we also call blk_put_queue() for them, and we expect the
request_queue refcount to reach 0 at this point, and so the request_queue
will also be freed prior to the disk.
Context
can sleep
-
void
disk_block_events(struct gendisk *disk)¶ block and flush disk event checking
Parameters
struct gendisk *disk- disk to block events for
Description
On return from this function, it is guaranteed that event checking
isn’t in progress and won’t happen until unblocked by
disk_unblock_events(). Events blocking is counted and the actual
unblocking happens after the matching number of unblocks are done.
Note that this intentionally does not block event checking from
disk_clear_events().
Context
Might sleep.
-
void
disk_unblock_events(struct gendisk *disk)¶ unblock disk event checking
Parameters
struct gendisk *disk- disk to unblock events for
Description
Undo disk_block_events(). When the block count reaches zero, it
starts events polling if configured.
Context
Don’t care. Safe to call from irq context.
-
void
disk_flush_events(struct gendisk *disk, unsigned int mask)¶ schedule immediate event checking and flushing
Parameters
struct gendisk *disk- disk to check and flush events for
unsigned int mask- events to flush
Description
Schedule immediate event checking on disk if not blocked. Events in mask are scheduled to be cleared from the driver. Note that this doesn’t clear the events from disk->ev.
Context
If mask is non-zero must be called with bdev->bd_mutex held.
-
unsigned int
disk_clear_events(struct gendisk *disk, unsigned int mask)¶ synchronously check, clear and return pending events
Parameters
struct gendisk *disk- disk to fetch and clear events from
unsigned int mask- mask of events to be fetched and cleared
Description
Disk events are synchronously checked and pending events in mask are cleared and returned. This ignores the block count.
Context
Might sleep.
-
void
disk_part_iter_init(struct disk_part_iter *piter, struct gendisk *disk, unsigned int flags)¶ initialize partition iterator
Parameters
struct disk_part_iter *piter- iterator to initialize
struct gendisk *disk- disk to iterate over
unsigned int flags- DISK_PITER_* flags
Description
Initialize piter so that it iterates over partitions of disk.
Context
Don’t care.
-
struct block_device *
disk_part_iter_next(struct disk_part_iter *piter)¶ proceed iterator to the next partition and return it
Parameters
struct disk_part_iter *piter- iterator of interest
Description
Proceed piter to the next partition and return it.
Context
Don’t care.
-
void
disk_part_iter_exit(struct disk_part_iter *piter)¶ finish up partition iteration
Parameters
struct disk_part_iter *piter- iter of interest
Description
Called when iteration is over. Cleans up piter.
Context
Don’t care.
-
bool
disk_has_partitions(struct gendisk *disk)¶
Parameters
struct gendisk *disk- gendisk of interest
Description
Walk through the partition table and check if valid partition exists.
Context
Don’t care.
Return
True if the gendisk has at least one valid non-zero size partition. Otherwise false.
-
int
__register_blkdev(unsigned int major, const char *name, void (*probe)(dev_t devt))¶ register a new block device
Parameters
unsigned int major- the requested major device number [1..BLKDEV_MAJOR_MAX-1]. If major = 0, try to allocate any unused major number.
const char *name- the name of the new block device as a zero terminated string
void (*probe)(dev_t devt)- allback that is called on access to any minor number of major
Description
The name must be unique within the system.
The return value depends on the major input parameter:
- if a major device number was requested in range [1..BLKDEV_MAJOR_MAX-1] then the function returns zero on success, or a negative error code
- if any unused major number was requested with major = 0 parameter then the return value is the allocated major number in range [1..BLKDEV_MAJOR_MAX-1] or a negative error code otherwise
See Linux allocated devices (4.x+ version) for the list of allocated major numbers.
Use register_blkdev instead for any new code.
-
void
del_gendisk(struct gendisk *disk)¶ remove the gendisk
Parameters
struct gendisk *disk- the struct gendisk to remove
Description
Removes the gendisk and all its associated resources. This deletes the partitions associated with the gendisk, and unregisters the associated request_queue.
This is the counter to the respective __device_add_disk() call.
The final removal of the struct gendisk happens when its refcount reaches 0
with put_disk(), which should be called after del_gendisk(), if
__device_add_disk() was used.
Drivers exist which depend on the release of the gendisk to be synchronous, it should not be deferred.
Context
can sleep
-
void
put_disk(struct gendisk *disk)¶ decrements the gendisk refcount
Parameters
struct gendisk *disk- the struct gendisk to decrement the refcount for
Description
This decrements the refcount for the struct gendisk. When this reaches 0
we’ll have disk_release() called.
Context
Any context, but the last reference must not be dropped from atomic context.
-
bool
bdev_check_media_change(struct block_device *bdev)¶ check if a removable media has been changed
Parameters
struct block_device *bdev- block device to check
Description
Check whether a removable media has been changed, and attempt to free all dentries and inodes and invalidates all block device page cache entries in that case.
Returns true if the block device changed, or false if not.
Char devices¶
-
int
register_chrdev_region(dev_t from, unsigned count, const char *name)¶ register a range of device numbers
Parameters
dev_t from- the first in the desired range of device numbers; must include the major number.
unsigned count- the number of consecutive device numbers required
const char *name- the name of the device or driver.
Description
Return value is zero on success, a negative error code on failure.
-
int
alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, const char *name)¶ register a range of char device numbers
Parameters
dev_t *dev- output parameter for first assigned number
unsigned baseminor- first of the requested range of minor numbers
unsigned count- the number of minor numbers required
const char *name- the name of the associated device or driver
Description
Allocates a range of char device numbers. The major number will be chosen dynamically, and returned (along with the first minor number) in dev. Returns zero or a negative error code.
-
int
__register_chrdev(unsigned int major, unsigned int baseminor, unsigned int count, const char *name, const struct file_operations *fops)¶ create and register a cdev occupying a range of minors
Parameters
unsigned int major- major device number or 0 for dynamic allocation
unsigned int baseminor- first of the requested range of minor numbers
unsigned int count- the number of minor numbers required
const char *name- name of this range of devices
const struct file_operations *fops- file operations associated with this devices
Description
If major == 0 this functions will dynamically allocate a major and return its number.
If major > 0 this function will attempt to reserve a device with the given major number and will return zero on success.
Returns a -ve errno on failure.
The name of this device has nothing to do with the name of the device in /dev. It only helps to keep track of the different owners of devices. If your module name has only one type of devices it’s ok to use e.g. the name of the module here.
-
void
unregister_chrdev_region(dev_t from, unsigned count)¶ unregister a range of device numbers
Parameters
dev_t from- the first in the range of numbers to unregister
unsigned count- the number of device numbers to unregister
Description
This function will unregister a range of count device numbers, starting with from. The caller should normally be the one who allocated those numbers in the first place…
-
void
__unregister_chrdev(unsigned int major, unsigned int baseminor, unsigned int count, const char *name)¶ unregister and destroy a cdev
Parameters
unsigned int major- major device number
unsigned int baseminor- first of the range of minor numbers
unsigned int count- the number of minor numbers this cdev is occupying
const char *name- name of this range of devices
Description
Unregister and destroy the cdev occupying the region described by
major, baseminor and count. This function undoes what
__register_chrdev() did.
-
int
cdev_add(struct cdev *p, dev_t dev, unsigned count)¶ add a char device to the system
Parameters
struct cdev *p- the cdev structure for the device
dev_t dev- the first device number for which this device is responsible
unsigned count- the number of consecutive minor numbers corresponding to this device
Description
cdev_add() adds the device represented by p to the system, making it
live immediately. A negative error code is returned on failure.
-
void
cdev_set_parent(struct cdev *p, struct kobject *kobj)¶ set the parent kobject for a char device
Parameters
struct cdev *p- the cdev structure
struct kobject *kobj- the kobject to take a reference to
Description
cdev_set_parent() sets a parent kobject which will be referenced
appropriately so the parent is not freed before the cdev. This
should be called before cdev_add.
-
int
cdev_device_add(struct cdev *cdev, struct device *dev)¶ add a char device and it’s corresponding
struct device, linkink
Parameters
struct cdev *cdev- the cdev structure
struct device *dev- the device structure
Description
cdev_device_add() adds the char device represented by cdev to the system,
just as cdev_add does. It then adds dev to the system using device_add
The dev_t for the char device will be taken from the struct device which
needs to be initialized first. This helper function correctly takes a
reference to the parent device so the parent will not get released until
all references to the cdev are released.
This helper uses dev->devt for the device number. If it is not set it will not add the cdev and it will be equivalent to device_add.
This function should be used whenever the struct cdev and the
struct device are members of the same structure whose lifetime is
managed by the struct device.
NOTE
Callers must assume that userspace was able to open the cdev and can call cdev fops callbacks at any time, even if this function fails.
Parameters
struct cdev *cdev- the cdev structure
struct device *dev- the device structure
Description
cdev_device_del() is a helper function to call cdev_del and device_del.
It should be used whenever cdev_device_add is used.
If dev->devt is not set it will not remove the cdev and will be equivalent to device_del.
NOTE
This guarantees that associated sysfs callbacks are not running or runnable, however any cdevs already open will remain and their fops will still be callable even after this function returns.
-
void
cdev_del(struct cdev *p)¶ remove a cdev from the system
Parameters
struct cdev *p- the cdev structure to be removed
Description
cdev_del() removes p from the system, possibly freeing the structure
itself.
NOTE
This guarantees that cdev device will no longer be able to be opened, however any cdevs already open will remain and their fops will still be callable even after cdev_del returns.
-
struct cdev *
cdev_alloc(void)¶ allocate a cdev structure
Parameters
void- no arguments
Description
Allocates and returns a cdev structure, or NULL on failure.
-
void
cdev_init(struct cdev *cdev, const struct file_operations *fops)¶ initialize a cdev structure
Parameters
struct cdev *cdev- the structure to initialize
const struct file_operations *fops- the file_operations for this device
Description
Initializes cdev, remembering fops, making it ready to add to the
system with cdev_add().
Clock Framework¶
The clock framework defines programming interfaces to support software
management of the system clock tree. This framework is widely used with
System-On-Chip (SOC) platforms to support power management and various
devices which may need custom clock rates. Note that these “clocks”
don’t relate to timekeeping or real time clocks (RTCs), each of which
have separate frameworks. These struct clk
instances may be used to manage for example a 96 MHz signal that is used
to shift bits into and out of peripherals or busses, or otherwise
trigger synchronous state machine transitions in system hardware.
Power management is supported by explicit software clock gating: unused clocks are disabled, so the system doesn’t waste power changing the state of transistors that aren’t in active use. On some systems this may be backed by hardware clock gating, where clocks are gated without being disabled in software. Sections of chips that are powered but not clocked may be able to retain their last state. This low power state is often called a retention mode. This mode still incurs leakage currents, especially with finer circuit geometries, but for CMOS circuits power is mostly used by clocked state changes.
Power-aware drivers only enable their clocks when the device they manage is in active use. Also, system sleep states often differ according to which clock domains are active: while a “standby” state may allow wakeup from several active domains, a “mem” (suspend-to-RAM) state may require a more wholesale shutdown of clocks derived from higher speed PLLs and oscillators, limiting the number of possible wakeup event sources. A driver’s suspend method may need to be aware of system-specific clock constraints on the target sleep state.
Some platforms support programmable clock generators. These can be used by external chips of various kinds, such as other CPUs, multimedia codecs, and devices with strict requirements for interface clocking.
-
struct
clk_notifier¶ associate a clk with a notifier
Definition
struct clk_notifier {
struct clk *clk;
struct srcu_notifier_head notifier_head;
struct list_head node;
};
Members
clk- struct clk * to associate the notifier with
notifier_head- a blocking_notifier_head for this clk
node- linked list pointers
Description
A list of struct clk_notifier is maintained by the notifier code.
An entry is created whenever code registers the first notifier on a
particular clk. Future notifiers on that clk are added to the
notifier_head.
-
struct
clk_notifier_data¶ rate data to pass to the notifier callback
Definition
struct clk_notifier_data {
struct clk *clk;
unsigned long old_rate;
unsigned long new_rate;
};
Members
clk- struct clk * being changed
old_rate- previous rate of this clk
new_rate- new rate of this clk
Description
For a pre-notifier, old_rate is the clk’s rate before this rate change, and new_rate is what the rate will be in the future. For a post-notifier, old_rate and new_rate are both set to the clk’s current rate (this was done to optimize the implementation).
-
struct
clk_bulk_data¶ Data used for bulk clk operations.
Definition
struct clk_bulk_data {
const char *id;
struct clk *clk;
};
Members
id- clock consumer ID
clk- struct clk * to store the associated clock
Description
The CLK APIs provide a series of clk_bulk_() API calls as a convenience to consumers which require multiple clks. This structure is used to manage data for these calls.
-
int
clk_notifier_register(struct clk *clk, struct notifier_block *nb)¶ change notifier callback
Parameters
struct clk *clk- clock whose rate we are interested in
struct notifier_block *nb- notifier block with callback function pointer
Description
ProTip: debugging across notifier chains can be frustrating. Make sure that your notifier callback function prints a nice big warning in case of failure.
-
int
clk_notifier_unregister(struct clk *clk, struct notifier_block *nb)¶ change notifier callback
Parameters
struct clk *clk- clock whose rate we are no longer interested in
struct notifier_block *nb- notifier block which will be unregistered
-
int
devm_clk_notifier_register(struct device *dev, struct clk *clk, struct notifier_block *nb)¶ register a managed rate-change notifier callback
Parameters
struct device *dev- device for clock “consumer”
struct clk *clk- clock whose rate we are interested in
struct notifier_block *nb- notifier block with callback function pointer
Description
Returns 0 on success, -EERROR otherwise
-
long
clk_get_accuracy(struct clk *clk)¶ obtain the clock accuracy in ppb (parts per billion) for a clock source.
Parameters
struct clk *clk- clock source
Description
This gets the clock source accuracy expressed in ppb. A perfect clock returns 0.
-
int
clk_set_phase(struct clk *clk, int degrees)¶ adjust the phase shift of a clock signal
Parameters
struct clk *clk- clock signal source
int degrees- number of degrees the signal is shifted
Description
Shifts the phase of a clock signal by the specified degrees. Returns 0 on success, -EERROR otherwise.
-
int
clk_get_phase(struct clk *clk)¶ return the phase shift of a clock signal
Parameters
struct clk *clk- clock signal source
Description
Returns the phase shift of a clock node in degrees, otherwise returns -EERROR.
-
int
clk_set_duty_cycle(struct clk *clk, unsigned int num, unsigned int den)¶ adjust the duty cycle ratio of a clock signal
Parameters
struct clk *clk- clock signal source
unsigned int num- numerator of the duty cycle ratio to be applied
unsigned int den- denominator of the duty cycle ratio to be applied
Description
Adjust the duty cycle of a clock signal by the specified ratio. Returns 0 on success, -EERROR otherwise.
-
int
clk_get_scaled_duty_cycle(struct clk *clk, unsigned int scale)¶ return the duty cycle ratio of a clock signal
Parameters
struct clk *clk- clock signal source
unsigned int scale- scaling factor to be applied to represent the ratio as an integer
Description
Returns the duty cycle ratio multiplied by the scale provided, otherwise returns -EERROR.
-
bool
clk_is_match(const struct clk *p, const struct clk *q)¶ check if two clk’s point to the same hardware clock
Parameters
const struct clk *p- clk compared against q
const struct clk *q- clk compared against p
Description
Returns true if the two struct clk pointers both point to the same hardware
clock node. Put differently, returns true if p and q
share the same struct clk_core object.
Returns false otherwise. Note that two NULL clks are treated as matching.
-
int
clk_prepare(struct clk *clk)¶ prepare a clock source
Parameters
struct clk *clk- clock source
Description
This prepares the clock source for use.
Must not be called from within atomic context.
-
void
clk_unprepare(struct clk *clk)¶ undo preparation of a clock source
Parameters
struct clk *clk- clock source
Description
This undoes a previously prepared clock. The caller must balance the number of prepare and unprepare calls.
Must not be called from within atomic context.
-
struct clk *
clk_get(struct device *dev, const char *id)¶ lookup and obtain a reference to a clock producer.
Parameters
struct device *dev- device for clock “consumer”
const char *id- clock consumer ID
Description
Returns a struct clk corresponding to the clock producer, or valid IS_ERR() condition containing errno. The implementation uses dev and id to determine the clock consumer, and thereby the clock producer. (IOW, id may be identical strings, but clk_get may return different clock producers depending on dev.)
Drivers must assume that the clock source is not enabled.
clk_get should not be called from within interrupt context.
-
int
clk_bulk_get(struct device *dev, int num_clks, struct clk_bulk_data *clks)¶ lookup and obtain a number of references to clock producer.
Parameters
struct device *dev- device for clock “consumer”
int num_clks- the number of clk_bulk_data
struct clk_bulk_data *clks- the clk_bulk_data table of consumer
Description
This helper function allows drivers to get several clk consumers in one operation. If any of the clk cannot be acquired then any clks that were obtained will be freed before returning to the caller.
Returns 0 if all clocks specified in clk_bulk_data table are obtained successfully, or valid IS_ERR() condition containing errno. The implementation uses dev and clk_bulk_data.id to determine the clock consumer, and thereby the clock producer. The clock returned is stored in each clk_bulk_data.clk field.
Drivers must assume that the clock source is not enabled.
clk_bulk_get should not be called from within interrupt context.
-
int
clk_bulk_get_all(struct device *dev, struct clk_bulk_data **clks)¶ lookup and obtain all available references to clock producer.
Parameters
struct device *dev- device for clock “consumer”
struct clk_bulk_data **clks- pointer to the clk_bulk_data table of consumer
Description
This helper function allows drivers to get all clk consumers in one operation. If any of the clk cannot be acquired then any clks that were obtained will be freed before returning to the caller.
Returns a positive value for the number of clocks obtained while the clock references are stored in the clk_bulk_data table in clks field. Returns 0 if there’re none and a negative value if something failed.
Drivers must assume that the clock source is not enabled.
clk_bulk_get should not be called from within interrupt context.
-
int
clk_bulk_get_optional(struct device *dev, int num_clks, struct clk_bulk_data *clks)¶ lookup and obtain a number of references to clock producer
Parameters
struct device *dev- device for clock “consumer”
int num_clks- the number of clk_bulk_data
struct clk_bulk_data *clks- the clk_bulk_data table of consumer
Description
Behaves the same as clk_bulk_get() except where there is no clock producer.
In this case, instead of returning -ENOENT, the function returns 0 and
NULL for a clk for which a clock producer could not be determined.
-
int
devm_clk_bulk_get(struct device *dev, int num_clks, struct clk_bulk_data *clks)¶ managed get multiple clk consumers
Parameters
struct device *dev- device for clock “consumer”
int num_clks- the number of clk_bulk_data
struct clk_bulk_data *clks- the clk_bulk_data table of consumer
Description
Return 0 on success, an errno on failure.
This helper function allows drivers to get several clk consumers in one operation with management, the clks will automatically be freed when the device is unbound.
-
int
devm_clk_bulk_get_optional(struct device *dev, int num_clks, struct clk_bulk_data *clks)¶ managed get multiple optional consumer clocks
Parameters
struct device *dev- device for clock “consumer”
int num_clks- the number of clk_bulk_data
struct clk_bulk_data *clks- pointer to the clk_bulk_data table of consumer
Description
Behaves the same as devm_clk_bulk_get() except where there is no clock
producer. In this case, instead of returning -ENOENT, the function returns
NULL for given clk. It is assumed all clocks in clk_bulk_data are optional.
Returns 0 if all clocks specified in clk_bulk_data table are obtained successfully or for any clk there was no clk provider available, otherwise returns valid IS_ERR() condition containing errno. The implementation uses dev and clk_bulk_data.id to determine the clock consumer, and thereby the clock producer. The clock returned is stored in each clk_bulk_data.clk field.
Drivers must assume that the clock source is not enabled.
clk_bulk_get should not be called from within interrupt context.
-
int
devm_clk_bulk_get_all(struct device *dev, struct clk_bulk_data **clks)¶ managed get multiple clk consumers
Parameters
struct device *dev- device for clock “consumer”
struct clk_bulk_data **clks- pointer to the clk_bulk_data table of consumer
Description
Returns a positive value for the number of clocks obtained while the clock references are stored in the clk_bulk_data table in clks field. Returns 0 if there’re none and a negative value if something failed.
This helper function allows drivers to get several clk consumers in one operation with management, the clks will automatically be freed when the device is unbound.
-
struct clk *
devm_clk_get(struct device *dev, const char *id)¶ lookup and obtain a managed reference to a clock producer.
Parameters
struct device *dev- device for clock “consumer”
const char *id- clock consumer ID
Description
Returns a struct clk corresponding to the clock producer, or valid IS_ERR() condition containing errno. The implementation uses dev and id to determine the clock consumer, and thereby the clock producer. (IOW, id may be identical strings, but clk_get may return different clock producers depending on dev.)
Drivers must assume that the clock source is not enabled.
devm_clk_get should not be called from within interrupt context.
The clock will automatically be freed when the device is unbound from the bus.
-
struct clk *
devm_clk_get_optional(struct device *dev, const char *id)¶ lookup and obtain a managed reference to an optional clock producer.
Parameters
struct device *dev- device for clock “consumer”
const char *id- clock consumer ID
Description
Behaves the same as devm_clk_get() except where there is no clock producer.
In this case, instead of returning -ENOENT, the function returns NULL.
-
struct clk *
devm_get_clk_from_child(struct device *dev, struct device_node *np, const char *con_id)¶ lookup and obtain a managed reference to a clock producer from child node.
Parameters
struct device *dev- device for clock “consumer”
struct device_node *np- pointer to clock consumer node
const char *con_id- clock consumer ID
Description
This function parses the clocks, and uses them to look up the struct clk from the registered list of clock providers by using np and con_id
The clock will automatically be freed when the device is unbound from the bus.
-
int
clk_rate_exclusive_get(struct clk *clk)¶ get exclusivity over the rate control of a producer
Parameters
struct clk *clk- clock source
Description
This function allows drivers to get exclusive control over the rate of a provider. It prevents any other consumer to execute, even indirectly, opereation which could alter the rate of the provider or cause glitches
If exlusivity is claimed more than once on clock, even by the same driver, the rate effectively gets locked as exclusivity can’t be preempted.
Must not be called from within atomic context.
Returns success (0) or negative errno.
-
void
clk_rate_exclusive_put(struct clk *clk)¶ release exclusivity over the rate control of a producer
Parameters
struct clk *clk- clock source
Description
This function allows drivers to release the exclusivity it previously got
from clk_rate_exclusive_get()
The caller must balance the number of clk_rate_exclusive_get() and
clk_rate_exclusive_put() calls.
Must not be called from within atomic context.
-
int
clk_enable(struct clk *clk)¶ inform the system when the clock source should be running.
Parameters
struct clk *clk- clock source
Description
If the clock can not be enabled/disabled, this should return success.
May be called from atomic contexts.
Returns success (0) or negative errno.
-
int
clk_bulk_enable(int num_clks, const struct clk_bulk_data *clks)¶ inform the system when the set of clks should be running.
Parameters
int num_clks- the number of clk_bulk_data
const struct clk_bulk_data *clks- the clk_bulk_data table of consumer
Description
May be called from atomic contexts.
Returns success (0) or negative errno.
-
void
clk_disable(struct clk *clk)¶ inform the system when the clock source is no longer required.
Parameters
struct clk *clk- clock source
Description
Inform the system that a clock source is no longer required by a driver and may be shut down.
May be called from atomic contexts.
Implementation detail: if the clock source is shared between
multiple drivers, clk_enable() calls must be balanced by the
same number of clk_disable() calls for the clock source to be
disabled.
-
void
clk_bulk_disable(int num_clks, const struct clk_bulk_data *clks)¶ inform the system when the set of clks is no longer required.
Parameters
int num_clks- the number of clk_bulk_data
const struct clk_bulk_data *clks- the clk_bulk_data table of consumer
Description
Inform the system that a set of clks is no longer required by a driver and may be shut down.
May be called from atomic contexts.
Implementation detail: if the set of clks is shared between
multiple drivers, clk_bulk_enable() calls must be balanced by the
same number of clk_bulk_disable() calls for the clock source to be
disabled.
-
unsigned long
clk_get_rate(struct clk *clk)¶ obtain the current clock rate (in Hz) for a clock source. This is only valid once the clock source has been enabled.
Parameters
struct clk *clk- clock source
-
void
clk_put(struct clk *clk)¶ “free” the clock source
Parameters
struct clk *clk- clock source
Note
drivers must ensure that all clk_enable calls made on this clock source are balanced by clk_disable calls prior to calling this function.
Description
clk_put should not be called from within interrupt context.
-
void
clk_bulk_put(int num_clks, struct clk_bulk_data *clks)¶ “free” the clock source
Parameters
int num_clks- the number of clk_bulk_data
struct clk_bulk_data *clks- the clk_bulk_data table of consumer
Note
drivers must ensure that all clk_bulk_enable calls made on this clock source are balanced by clk_bulk_disable calls prior to calling this function.
Description
clk_bulk_put should not be called from within interrupt context.
-
void
clk_bulk_put_all(int num_clks, struct clk_bulk_data *clks)¶ “free” all the clock source
Parameters
int num_clks- the number of clk_bulk_data
struct clk_bulk_data *clks- the clk_bulk_data table of consumer
Note
drivers must ensure that all clk_bulk_enable calls made on this clock source are balanced by clk_bulk_disable calls prior to calling this function.
Description
clk_bulk_put_all should not be called from within interrupt context.
Parameters
struct device *dev- device used to acquire the clock
struct clk *clk- clock source acquired with
devm_clk_get()
Note
drivers must ensure that all clk_enable calls made on this clock source are balanced by clk_disable calls prior to calling this function.
Description
clk_put should not be called from within interrupt context.
-
long
clk_round_rate(struct clk *clk, unsigned long rate)¶ adjust a rate to the exact rate a clock can provide
Parameters
struct clk *clk- clock source
unsigned long rate- desired clock rate in Hz
Description
This answers the question “if I were to pass rate to clk_set_rate(),
what clock rate would I end up with?” without changing the hardware
in any way. In other words:
rate = clk_round_rate(clk, r);
and:
clk_set_rate(clk, r); rate = clk_get_rate(clk);
are equivalent except the former does not modify the clock hardware in any way.
Returns rounded clock rate in Hz, or negative errno.
-
int
clk_set_rate(struct clk *clk, unsigned long rate)¶ set the clock rate for a clock source
Parameters
struct clk *clk- clock source
unsigned long rate- desired clock rate in Hz
Description
Updating the rate starts at the top-most affected clock and then walks the tree down to the bottom-most clock that needs updating.
Returns success (0) or negative errno.
-
int
clk_set_rate_exclusive(struct clk *clk, unsigned long rate)¶ set the clock rate and claim exclusivity over clock source
Parameters
struct clk *clk- clock source
unsigned long rate- desired clock rate in Hz
Description
This helper function allows drivers to atomically set the rate of a producer and claim exclusivity over the rate control of the producer.
It is essentially a combination of clk_set_rate() and
clk_rate_exclusite_get(). Caller must balance this call with a call to
clk_rate_exclusive_put()
Returns success (0) or negative errno.
-
bool
clk_has_parent(struct clk *clk, struct clk *parent)¶ check if a clock is a possible parent for another
Parameters
struct clk *clk- clock source
struct clk *parent- parent clock source
Description
This function can be used in drivers that need to check that a clock can be the parent of another without actually changing the parent.
Returns true if parent is a possible parent for clk, false otherwise.
-
int
clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max)¶ set a rate range for a clock source
Parameters
struct clk *clk- clock source
unsigned long min- desired minimum clock rate in Hz, inclusive
unsigned long max- desired maximum clock rate in Hz, inclusive
Description
Returns success (0) or negative errno.
-
int
clk_set_min_rate(struct clk *clk, unsigned long rate)¶ set a minimum clock rate for a clock source
Parameters
struct clk *clk- clock source
unsigned long rate- desired minimum clock rate in Hz, inclusive
Description
Returns success (0) or negative errno.
-
int
clk_set_max_rate(struct clk *clk, unsigned long rate)¶ set a maximum clock rate for a clock source
Parameters
struct clk *clk- clock source
unsigned long rate- desired maximum clock rate in Hz, inclusive
Description
Returns success (0) or negative errno.
-
int
clk_set_parent(struct clk *clk, struct clk *parent)¶ set the parent clock source for this clock
Parameters
struct clk *clk- clock source
struct clk *parent- parent clock source
Description
Returns success (0) or negative errno.
-
struct clk *
clk_get_parent(struct clk *clk)¶ get the parent clock source for this clock
Parameters
struct clk *clk- clock source
Description
Returns struct clk corresponding to parent clock source, or valid IS_ERR() condition containing errno.
-
struct clk *
clk_get_sys(const char *dev_id, const char *con_id)¶ get a clock based upon the device name
Parameters
const char *dev_id- device name
const char *con_id- connection ID
Description
Returns a struct clk corresponding to the clock producer, or
valid IS_ERR() condition containing errno. The implementation
uses dev_id and con_id to determine the clock consumer, and
thereby the clock producer. In contrast to clk_get() this function
takes the device name instead of the device itself for identification.
Drivers must assume that the clock source is not enabled.
clk_get_sys should not be called from within interrupt context.
-
int
clk_save_context(void)¶ save clock context for poweroff
Parameters
void- no arguments
Description
Saves the context of the clock register for powerstates in which the contents of the registers will be lost. Occurs deep within the suspend code so locking is not necessary.
-
void
clk_restore_context(void)¶ restore clock context after poweroff
Parameters
void- no arguments
Description
This occurs with all clocks enabled. Occurs deep within the resume code so locking is not necessary.
-
struct clk *
clk_get_optional(struct device *dev, const char *id)¶ lookup and obtain a reference to an optional clock producer.
Parameters
struct device *dev- device for clock “consumer”
const char *id- clock consumer ID
Description
Behaves the same as clk_get() except where there is no clock producer. In
this case, instead of returning -ENOENT, the function returns NULL.
Synchronization Primitives¶
Read-Copy Update (RCU)¶
-
RCU_NONIDLE(a)¶ Indicate idle-loop code that needs RCU readers
Parameters
a- Code that RCU needs to pay attention to.
Description
RCU read-side critical sections are forbidden in the inner idle loop,
that is, between the rcu_idle_enter() and the rcu_idle_exit() – RCU
will happily ignore any such read-side critical sections. However,
things like powertop need tracepoints in the inner idle loop.
This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
will tell RCU that it needs to pay attention, invoke its argument
(in this example, calling the do_something_with_RCU() function),
and then tell RCU to go back to ignoring this CPU. It is permissible
to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
on the order of a million or so, even on 32-bit systems). It is
not legal to block within RCU_NONIDLE(), nor is it permissible to
transfer control either into or out of RCU_NONIDLE()’s statement.
-
cond_resched_tasks_rcu_qs()¶ Report potential quiescent states to RCU
Parameters
Description
This macro resembles cond_resched(), except that it is defined to report potential quiescent states to RCU-tasks even if the cond_resched() machinery were to be shut off, as some advocate for PREEMPTION kernels.
-
RCU_LOCKDEP_WARN(c, s)¶ emit lockdep splat if specified condition is met
Parameters
c- condition to check
s- informative message
-
RCU_INITIALIZER(v)¶ statically initialize an RCU-protected global variable
Parameters
v- The value to statically initialize with.
-
rcu_assign_pointer(p, v)¶ assign to RCU-protected pointer
Parameters
p- pointer to assign to
v- value to assign (publish)
Description
Assigns the specified value to the specified RCU-protected pointer, ensuring that any concurrent RCU readers will see any prior initialization.
Inserts memory barriers on architectures that require them (which is most of them), and also prevents the compiler from reordering the code that initializes the structure after the pointer assignment. More importantly, this call documents which pointers will be dereferenced by RCU read-side code.
In some special cases, you may use RCU_INIT_POINTER() instead
of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
to the fact that it does not constrain either the CPU or the compiler.
That said, using RCU_INIT_POINTER() when you should have used
rcu_assign_pointer() is a very bad thing that results in
impossible-to-diagnose memory corruption. So please be careful.
See the RCU_INIT_POINTER() comment header for details.
Note that rcu_assign_pointer() evaluates each of its arguments only
once, appearances notwithstanding. One of the “extra” evaluations
is in typeof() and the other visible only to sparse (__CHECKER__),
neither of which actually execute the argument. As with most cpp
macros, this execute-arguments-only-once property is important, so
please be careful when making changes to rcu_assign_pointer() and the
other macros that it invokes.
-
rcu_replace_pointer(rcu_ptr, ptr, c)¶ replace an RCU pointer, returning its old value
Parameters
rcu_ptr- RCU pointer, whose old value is returned
ptr- regular pointer
c- the lockdep conditions under which the dereference will take place
Description
Perform a replacement, where rcu_ptr is an RCU-annotated
pointer and c is the lockdep argument that is passed to the
rcu_dereference_protected() call used to read that pointer. The old
value of rcu_ptr is returned, and rcu_ptr is set to ptr.
-
rcu_access_pointer(p)¶ fetch RCU pointer with no dereferencing
Parameters
p- The pointer to read
Description
Return the value of the specified RCU-protected pointer, but omit the
lockdep checks for being in an RCU read-side critical section. This is
useful when the value of this pointer is accessed, but the pointer is
not dereferenced, for example, when testing an RCU-protected pointer
against NULL. Although rcu_access_pointer() may also be used in cases
where update-side locks prevent the value of the pointer from changing,
you should instead use rcu_dereference_protected() for this use case.
It is also permissible to use rcu_access_pointer() when read-side
access to the pointer was removed at least one grace period ago, as
is the case in the context of the RCU callback that is freeing up
the data, or after a synchronize_rcu() returns. This can be useful
when tearing down multi-linked structures after a grace period
has elapsed.
-
rcu_dereference_check(p, c)¶ rcu_dereference with debug checking
Parameters
p- The pointer to read, prior to dereferencing
c- The conditions under which the dereference will take place
Description
Do an rcu_dereference(), but check that the conditions under which the
dereference will take place are correct. Typically the conditions
indicate the various locking conditions that should be held at that
point. The check should return true if the conditions are satisfied.
An implicit check for being in an RCU read-side critical section
(rcu_read_lock()) is included.
For example:
bar = rcu_dereference_check(foo->bar, lockdep_is_held(foo->lock));
could be used to indicate to lockdep that foo->bar may only be dereferenced
if either rcu_read_lock() is held, or that the lock required to replace
the bar struct at foo->bar is held.
Note that the list of conditions may also include indications of when a lock need not be held, for example during initialisation or destruction of the target struct:
- bar = rcu_dereference_check(foo->bar, lockdep_is_held(
foo->lock) ||- atomic_read(
foo->usage) == 0);
Inserts memory barriers on architectures that require them (currently only the Alpha), prevents the compiler from refetching (and from merging fetches), and, more importantly, documents exactly which pointers are protected by RCU and checks that the pointer is annotated as __rcu.
-
rcu_dereference_bh_check(p, c)¶ rcu_dereference_bh with debug checking
Parameters
p- The pointer to read, prior to dereferencing
c- The conditions under which the dereference will take place
Description
This is the RCU-bh counterpart to rcu_dereference_check().
-
rcu_dereference_sched_check(p, c)¶ rcu_dereference_sched with debug checking
Parameters
p- The pointer to read, prior to dereferencing
c- The conditions under which the dereference will take place
Description
This is the RCU-sched counterpart to rcu_dereference_check().
-
rcu_dereference_protected(p, c)¶ fetch RCU pointer when updates prevented
Parameters
p- The pointer to read, prior to dereferencing
c- The conditions under which the dereference will take place
Description
Return the value of the specified RCU-protected pointer, but omit the READ_ONCE(). This is useful in cases where update-side locks prevent the value of the pointer from changing. Please note that this primitive does not prevent the compiler from repeating this reference or combining it with other references, so it should not be used without protection of appropriate locks.
This function is only for update-side use. Using this function
when protected only by rcu_read_lock() will result in infrequent
but very ugly failures.
-
rcu_dereference(p)¶ fetch RCU-protected pointer for dereferencing
Parameters
p- The pointer to read, prior to dereferencing
Description
This is a simple wrapper around rcu_dereference_check().
-
rcu_dereference_bh(p)¶ fetch an RCU-bh-protected pointer for dereferencing
Parameters
p- The pointer to read, prior to dereferencing
Description
Makes rcu_dereference_check() do the dirty work.
-
rcu_dereference_sched(p)¶ fetch RCU-sched-protected pointer for dereferencing
Parameters
p- The pointer to read, prior to dereferencing
Description
Makes rcu_dereference_check() do the dirty work.
-
rcu_pointer_handoff(p)¶ Hand off a pointer from RCU to other mechanism
Parameters
p- The pointer to hand off
Description
This is simply an identity function, but it documents where a pointer is handed off from RCU to some other synchronization mechanism, for example, reference counting or locking. In C11, it would map to kill_dependency(). It could be used as follows:
rcu_read_lock();
p = rcu_dereference(gp);
long_lived = is_long_lived(p);
if (long_lived) {
if (!atomic_inc_not_zero(p->refcnt))
long_lived = false;
else
p = rcu_pointer_handoff(p);
}
rcu_read_unlock();
-
void
rcu_read_lock(void)¶ mark the beginning of an RCU read-side critical section
Parameters
void- no arguments
Description
When synchronize_rcu() is invoked on one CPU while other CPUs
are within RCU read-side critical sections, then the
synchronize_rcu() is guaranteed to block until after all the other
CPUs exit their critical sections. Similarly, if call_rcu() is invoked
on one CPU while other CPUs are within RCU read-side critical
sections, invocation of the corresponding RCU callback is deferred
until after the all the other CPUs exit their critical sections.
Note, however, that RCU callbacks are permitted to run concurrently
with new RCU read-side critical sections. One way that this can happen
is via the following sequence of events: (1) CPU 0 enters an RCU
read-side critical section, (2) CPU 1 invokes call_rcu() to register
an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
(4) CPU 2 enters a RCU read-side critical section, (5) the RCU
callback is invoked. This is legal, because the RCU read-side critical
section that was running concurrently with the call_rcu() (and which
therefore might be referencing something that the corresponding RCU
callback would free up) has completed before the corresponding
RCU callback is invoked.
RCU read-side critical sections may be nested. Any deferred actions will be deferred until the outermost RCU read-side critical section completes.
You can avoid reading and understanding the next paragraph by
following this rule: don’t put anything in an rcu_read_lock() RCU
read-side critical section that would block in a !PREEMPTION kernel.
But if you want the full story, read on!
In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU), it is illegal to block while in an RCU read-side critical section. In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION kernel builds, RCU read-side critical sections may be preempted, but explicit blocking is illegal. Finally, in preemptible RCU implementations in real-time (with -rt patchset) kernel builds, RCU read-side critical sections may be preempted and they may also block, but only when acquiring spinlocks that are subject to priority inheritance.
-
void
rcu_read_unlock(void)¶ marks the end of an RCU read-side critical section.
Parameters
void- no arguments
Description
In most situations, rcu_read_unlock() is immune from deadlock.
However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
is responsible for deboosting, which it does via rt_mutex_unlock().
Unfortunately, this function acquires the scheduler’s runqueue and
priority-inheritance spinlocks. This means that deadlock could result
if the caller of rcu_read_unlock() already holds one of these locks or
any lock that is ever acquired while holding them.
That said, RCU readers are never priority boosted unless they were
preempted. Therefore, one way to avoid deadlock is to make sure
that preemption never happens within any RCU read-side critical
section whose outermost rcu_read_unlock() is called with one of
rt_mutex_unlock()’s locks held. Such preemption can be avoided in
a number of ways, for example, by invoking preempt_disable() before
critical section’s outermost rcu_read_lock().
Given that the set of locks acquired by rt_mutex_unlock() might change
at any time, a somewhat more future-proofed approach is to make sure
that that preemption never happens within any RCU read-side critical
section whose outermost rcu_read_unlock() is called with irqs disabled.
This approach relies on the fact that rt_mutex_unlock() currently only
acquires irq-disabled locks.
The second of these two approaches is best in most situations, however, the first approach can also be useful, at least to those developers willing to keep abreast of the set of locks acquired by rt_mutex_unlock().
See rcu_read_lock() for more information.
-
void
rcu_read_lock_bh(void)¶ mark the beginning of an RCU-bh critical section
Parameters
void- no arguments
Description
This is equivalent of rcu_read_lock(), but also disables softirqs.
Note that anything else that disables softirqs can also serve as
an RCU read-side critical section.
Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
must occur in the same context, for example, it is illegal to invoke
rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
was invoked from some other task.
-
void
rcu_read_unlock_bh(void)¶ marks the end of a softirq-only RCU critical section
Parameters
void- no arguments
Description
See rcu_read_lock_bh() for more information.
-
void
rcu_read_lock_sched(void)¶ mark the beginning of a RCU-sched critical section
Parameters
void- no arguments
Description
This is equivalent of rcu_read_lock(), but disables preemption.
Read-side critical sections can also be introduced by anything else
that disables preemption, including local_irq_disable() and friends.
Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
must occur in the same context, for example, it is illegal to invoke
rcu_read_unlock_sched() from process context if the matching
rcu_read_lock_sched() was invoked from an NMI handler.
-
void
rcu_read_unlock_sched(void)¶ marks the end of a RCU-classic critical section
Parameters
void- no arguments
Description
See rcu_read_lock_sched() for more information.
-
RCU_INIT_POINTER(p, v)¶ initialize an RCU protected pointer
Parameters
p- The pointer to be initialized.
v- The value to initialized the pointer to.
Description
Initialize an RCU-protected pointer in special cases where readers do not need ordering constraints on the CPU or the compiler. These special cases are:
- This use of
RCU_INIT_POINTER()is NULLing out the pointer or - The caller has taken whatever steps are required to prevent RCU readers from concurrently accessing this pointer or
- The referenced data structure has already been exposed to
readers either at compile time or via
rcu_assign_pointer()and- You have not made any reader-visible changes to this structure since then or
- It is OK for readers accessing this structure from its new location to see the old state of the structure. (For example, the changes were to statistical counters or to other state where exact synchronization is not required.)
Failure to follow these rules governing use of RCU_INIT_POINTER() will
result in impossible-to-diagnose memory corruption. As in the structures
will look OK in crash dumps, but any concurrent RCU readers might
see pre-initialized values of the referenced data structure. So
please be very careful how you use RCU_INIT_POINTER()!!!
If you are creating an RCU-protected linked structure that is accessed
by a single external-to-structure RCU-protected pointer, then you may
use RCU_INIT_POINTER() to initialize the internal RCU-protected
pointers, but you must use rcu_assign_pointer() to initialize the
external-to-structure pointer after you have completely initialized
the reader-accessible portions of the linked structure.
Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
ordering guarantees for either the CPU or the compiler.
-
RCU_POINTER_INITIALIZER(p, v)¶ statically initialize an RCU protected pointer
Parameters
p- The pointer to be initialized.
v- The value to initialized the pointer to.
Description
GCC-style initialization for an RCU-protected pointer in a structure field.
-
kfree_rcu(ptr, rhf)¶ kfree an object after a grace period.
Parameters
ptr- pointer to kfree
rhf- the name of the struct rcu_head within the type of ptr.
Description
Many rcu callbacks functions just call kfree() on the base structure.
These functions are trivial, but their size adds up, and furthermore
when they are used in a kernel module, that module must invoke the
high-latency rcu_barrier() function at module-unload time.
The kfree_rcu() function handles this issue. Rather than encoding a
function address in the embedded rcu_head structure, kfree_rcu() instead
encodes the offset of the rcu_head structure within the base structure.
Because the functions are not allowed in the low-order 4096 bytes of
kernel virtual memory, offsets up to 4095 bytes can be accommodated.
If the offset is larger than 4095 bytes, a compile-time error will
be generated in __kvfree_rcu(). If this error is triggered, you can
either fall back to use of call_rcu() or rearrange the structure to
position the rcu_head structure into the first 4096 bytes.
Note that the allowable offset might decrease in the future, for example, to allow something like kmem_cache_free_rcu().
The BUILD_BUG_ON check must not involve any function calls, hence the checks are done in macros here.
-
kvfree_rcu(…)¶ kvfree an object after a grace period.
Parameters
...- variable arguments
Description
This macro consists of one or two arguments and it is based on whether an object is head-less or not. If it has a head then a semantic stays the same as it used to be before:
kvfree_rcu(ptr, rhf);
where ptr is a pointer to kvfree(), rhf is the name
of the rcu_head structure within the type of ptr.
When it comes to head-less variant, only one argument is passed and that is just a pointer which has to be freed after a grace period. Therefore the semantic is
kvfree_rcu(ptr);
where ptr is a pointer to kvfree().
Please note, head-less way of freeing is permitted to
use from a context that has to follow might_sleep()
annotation. Otherwise, please switch and embed the
rcu_head structure within the type of ptr.
-
void
rcu_head_init(struct rcu_head *rhp)¶ Initialize rcu_head for
rcu_head_after_call_rcu()
Parameters
struct rcu_head *rhp- The rcu_head structure to initialize.
Description
If you intend to invoke rcu_head_after_call_rcu() to test whether a
given rcu_head structure has already been passed to call_rcu(), then
you must also invoke this rcu_head_init() function on it just after
allocating that structure. Calls to this function must not race with
calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
-
bool
rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)¶ Has this rcu_head been passed to
call_rcu()?
Parameters
struct rcu_head *rhp- The rcu_head structure to test.
rcu_callback_t f- The function passed to
call_rcu()along with rhp.
Description
Returns true if the rhp has been passed to call_rcu() with func,
and false otherwise. Emits a warning in any other case, including
the case where rhp has already been invoked after a grace period.
Calls to this function must not race with callback invocation. One way
to avoid such races is to enclose the call to rcu_head_after_call_rcu()
in an RCU read-side critical section that includes a read-side fetch
of the pointer to the structure containing rhp.
-
int
rcu_is_cpu_rrupt_from_idle(void)¶ see if ‘interrupted’ from idle
Parameters
void- no arguments
Description
If the current CPU is idle and running at a first-level (not nested) interrupt, or directly, from idle, return true.
The caller must have at least disabled IRQs.
-
void
rcu_idle_enter(void)¶ inform RCU that current CPU is entering idle
Parameters
void- no arguments
Description
Enter idle mode, in other words, -leave- the mode in which RCU read-side critical sections can occur. (Though RCU read-side critical sections can occur in irq handlers in idle, a possibility handled by irq_enter() and irq_exit().)
If you add or remove a call to rcu_idle_enter(), be sure to test with
CONFIG_RCU_EQS_DEBUG=y.
-
noinstr void
rcu_user_enter(void)¶ inform RCU that we are resuming userspace.
Parameters
void- no arguments
Description
Enter RCU idle mode right before resuming userspace. No use of RCU
is permitted between this call and rcu_user_exit(). This way the
CPU doesn’t need to maintain the tick for RCU maintenance purposes
when the CPU runs in userspace.
If you add or remove a call to rcu_user_enter(), be sure to test with
CONFIG_RCU_EQS_DEBUG=y.
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noinstr void
rcu_nmi_exit(void)¶ inform RCU of exit from NMI context
Parameters
void- no arguments
Description
If we are returning from the outermost NMI handler that interrupted an RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting to let the RCU grace-period handling know that the CPU is back to being RCU-idle.
If you add or remove a call to rcu_nmi_exit(), be sure to test
with CONFIG_RCU_EQS_DEBUG=y.
-
void noinstr
rcu_irq_exit(void)¶ inform RCU that current CPU is exiting irq towards idle
Parameters
void- no arguments
Description
Exit from an interrupt handler, which might possibly result in entering idle mode, in other words, leaving the mode in which read-side critical sections can occur. The caller must have disabled interrupts.
This code assumes that the idle loop never does anything that might result in unbalanced calls to irq_enter() and irq_exit(). If your architecture’s idle loop violates this assumption, RCU will give you what you deserve, good and hard. But very infrequently and irreproducibly.
Use things like work queues to work around this limitation.
You have been warned.
If you add or remove a call to rcu_irq_exit(), be sure to test with
CONFIG_RCU_EQS_DEBUG=y.
-
void
rcu_irq_exit_preempt(void)¶ Inform RCU that current CPU is exiting irq towards in kernel preemption
Parameters
void- no arguments
Description
Same as rcu_irq_exit() but has a sanity check that scheduling is safe
from RCU point of view. Invoked from return from interrupt before kernel
preemption.
-
void
rcu_irq_exit_check_preempt(void)¶ Validate that scheduling is possible
Parameters
void- no arguments
-
void
rcu_idle_exit(void)¶ inform RCU that current CPU is leaving idle
Parameters
void- no arguments
Description
Exit idle mode, in other words, -enter- the mode in which RCU read-side critical sections can occur.
If you add or remove a call to rcu_idle_exit(), be sure to test with
CONFIG_RCU_EQS_DEBUG=y.
-
void noinstr
rcu_user_exit(void)¶ inform RCU that we are exiting userspace.
Parameters
void- no arguments
Description
Exit RCU idle mode while entering the kernel because it can run a RCU read side critical section anytime.
If you add or remove a call to rcu_user_exit(), be sure to test with
CONFIG_RCU_EQS_DEBUG=y.
-
void
__rcu_irq_enter_check_tick(void)¶ Enable scheduler tick on CPU if RCU needs it.
Parameters
void- no arguments
Description
The scheduler tick is not normally enabled when CPUs enter the kernel from nohz_full userspace execution. After all, nohz_full userspace execution is an RCU quiescent state and the time executing in the kernel is quite short. Except of course when it isn’t. And it is not hard to cause a large system to spend tens of seconds or even minutes looping in the kernel, which can cause a number of problems, include RCU CPU stall warnings.
Therefore, if a nohz_full CPU fails to report a quiescent state in a timely manner, the RCU grace-period kthread sets that CPU’s ->rcu_urgent_qs flag with the expectation that the next interrupt or exception will invoke this function, which will turn on the scheduler tick, which will enable RCU to detect that CPU’s quiescent states, for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels. The tick will be disabled once a quiescent state is reported for this CPU.
Of course, in carefully tuned systems, there might never be an interrupt or exception. In that case, the RCU grace-period kthread will eventually cause one to happen. However, in less carefully controlled environments, this function allows RCU to get what it needs without creating otherwise useless interruptions.
-
noinstr void
rcu_nmi_enter(void)¶ inform RCU of entry to NMI context
Parameters
void- no arguments
Description
If the CPU was idle from RCU’s viewpoint, update rdp->dynticks and rdp->dynticks_nmi_nesting to let the RCU grace-period handling know that the CPU is active. This implementation permits nested NMIs, as long as the nesting level does not overflow an int. (You will probably run out of stack space first.)
If you add or remove a call to rcu_nmi_enter(), be sure to test
with CONFIG_RCU_EQS_DEBUG=y.
-
noinstr void
rcu_irq_enter(void)¶ inform RCU that current CPU is entering irq away from idle
Parameters
void- no arguments
Description
Enter an interrupt handler, which might possibly result in exiting idle mode, in other words, entering the mode in which read-side critical sections can occur. The caller must have disabled interrupts.
Note that the Linux kernel is fully capable of entering an interrupt handler that it never exits, for example when doing upcalls to user mode! This code assumes that the idle loop never does upcalls to user mode. If your architecture’s idle loop does do upcalls to user mode (or does anything else that results in unbalanced calls to the irq_enter() and irq_exit() functions), RCU will give you what you deserve, good and hard. But very infrequently and irreproducibly.
Use things like work queues to work around this limitation.
You have been warned.
If you add or remove a call to rcu_irq_enter(), be sure to test with
CONFIG_RCU_EQS_DEBUG=y.
-
notrace bool
rcu_is_watching(void)¶ see if RCU thinks that the current CPU is not idle
Parameters
void- no arguments
Description
Return true if RCU is watching the running CPU, which means that this CPU can safely enter RCU read-side critical sections. In other words, if the current CPU is not in its idle loop or is in an interrupt or NMI handler, return true.
Make notrace because it can be called by the internal functions of ftrace, and making this notrace removes unnecessary recursion calls.
-
void
call_rcu(struct rcu_head *head, rcu_callback_t func)¶ Queue an RCU callback for invocation after a grace period.
Parameters
struct rcu_head *head- structure to be used for queueing the RCU updates.
rcu_callback_t func- actual callback function to be invoked after the grace period
Description
The callback function will be invoked some time after a full grace
period elapses, in other words after all pre-existing RCU read-side
critical sections have completed. However, the callback function
might well execute concurrently with RCU read-side critical sections
that started after call_rcu() was invoked. RCU read-side critical
sections are delimited by rcu_read_lock() and rcu_read_unlock(), and
may be nested. In addition, regions of code across which interrupts,
preemption, or softirqs have been disabled also serve as RCU read-side
critical sections. This includes hardware interrupt handlers, softirq
handlers, and NMI handlers.
Note that all CPUs must agree that the grace period extended beyond
all pre-existing RCU read-side critical section. On systems with more
than one CPU, this means that when “func()” is invoked, each CPU is
guaranteed to have executed a full memory barrier since the end of its
last RCU read-side critical section whose beginning preceded the call
to call_rcu(). It also means that each CPU executing an RCU read-side
critical section that continues beyond the start of “func()” must have
executed a memory barrier after the call_rcu() but before the beginning
of that RCU read-side critical section. Note that these guarantees
include CPUs that are offline, idle, or executing in user mode, as
well as CPUs that are executing in the kernel.
Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
resulting RCU callback function “func()”, then both CPU A and CPU B are
guaranteed to execute a full memory barrier during the time interval
between the call to call_rcu() and the invocation of “func()” – even
if CPU A and CPU B are the same CPU (but again only if the system has
more than one CPU).
-
struct
kvfree_rcu_bulk_data¶ single block to store
kvfree_rcu()pointers
Definition
struct kvfree_rcu_bulk_data {
unsigned long nr_records;
struct kvfree_rcu_bulk_data *next;
void *records[];
};
Members
nr_records- Number of active pointers in the array
next- Next bulk object in the block chain
records- Array of the
kvfree_rcu()pointers
-
struct
kfree_rcu_cpu_work¶ single batch of
kfree_rcu()requests
Definition
struct kfree_rcu_cpu_work {
struct rcu_work rcu_work;
struct rcu_head *head_free;
struct kvfree_rcu_bulk_data *bkvhead_free[FREE_N_CHANNELS];
struct kfree_rcu_cpu *krcp;
};
Members
rcu_work- Let
queue_rcu_work()invoke workqueue handler after grace period head_free- List of
kfree_rcu()objects waiting for a grace period bkvhead_free- Bulk-List of
kvfree_rcu()objects waiting for a grace period krcp- Pointer to kfree_rcu_cpu structure
-
struct
kfree_rcu_cpu¶ batch up
kfree_rcu()requests for RCU grace period
Definition
struct kfree_rcu_cpu {
struct rcu_head *head;
struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS];
struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
raw_spinlock_t lock;
struct delayed_work monitor_work;
bool monitor_todo;
bool initialized;
int count;
struct work_struct page_cache_work;
atomic_t work_in_progress;
struct hrtimer hrtimer;
struct llist_head bkvcache;
int nr_bkv_objs;
};
Members
head- List of
kfree_rcu()objects not yet waiting for a grace period bkvhead- Bulk-List of
kvfree_rcu()objects not yet waiting for a grace period krw_arr- Array of batches of
kfree_rcu()objects waiting for a grace period lock- Synchronize access to this structure
monitor_work- Promote head to head_free after KFREE_DRAIN_JIFFIES
monitor_todo- Tracks whether a monitor_work delayed work is pending
initialized- The rcu_work fields have been initialized
count- Number of objects for which GP not started
page_cache_work- A work to refill the cache when it is empty
work_in_progress- Indicates that page_cache_work is running
hrtimer- A hrtimer for scheduling a page_cache_work
bkvcache- A simple cache list that contains objects for reuse purpose. In order to save some per-cpu space the list is singular. Even though it is lockless an access has to be protected by the per-cpu lock.
nr_bkv_objs- number of allocated objects at bkvcache.
Description
This is a per-CPU structure. The reason that it is not included in the rcu_data structure is to permit this code to be extracted from the RCU files. Such extraction could allow further optimization of the interactions with the slab allocators.
-
void
synchronize_rcu(void)¶ wait until a grace period has elapsed.
Parameters
void- no arguments
Description
Control will return to the caller some time after a full grace
period has elapsed, in other words after all currently executing RCU
read-side critical sections have completed. Note, however, that
upon return from synchronize_rcu(), the caller might well be executing
concurrently with new RCU read-side critical sections that began while
synchronize_rcu() was waiting. RCU read-side critical sections are
delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
In addition, regions of code across which interrupts, preemption, or
softirqs have been disabled also serve as RCU read-side critical
sections. This includes hardware interrupt handlers, softirq handlers,
and NMI handlers.
Note that this guarantee implies further memory-ordering guarantees.
On systems with more than one CPU, when synchronize_rcu() returns,
each CPU is guaranteed to have executed a full memory barrier since
the end of its last RCU read-side critical section whose beginning
preceded the call to synchronize_rcu(). In addition, each CPU having
an RCU read-side critical section that extends beyond the return from
synchronize_rcu() is guaranteed to have executed a full memory barrier
after the beginning of synchronize_rcu() and before the beginning of
that RCU read-side critical section. Note that these guarantees include
CPUs that are offline, idle, or executing in user mode, as well as CPUs
that are executing in the kernel.
Furthermore, if CPU A invoked synchronize_rcu(), which returned
to its caller on CPU B, then both CPU A and CPU B are guaranteed
to have executed a full memory barrier during the execution of
synchronize_rcu() – even if CPU A and CPU B are the same CPU (but
again only if the system has more than one CPU).
-
unsigned long
get_state_synchronize_rcu(void)¶ Snapshot current RCU state
Parameters
void- no arguments
Description
Returns a cookie that is used by a later call to cond_synchronize_rcu()
to determine whether or not a full grace period has elapsed in the
meantime.
-
void
cond_synchronize_rcu(unsigned long oldstate)¶ Conditionally wait for an RCU grace period
Parameters
unsigned long oldstate- return value from earlier call to
get_state_synchronize_rcu()
Description
If a full RCU grace period has elapsed since the earlier call to
get_state_synchronize_rcu(), just return. Otherwise, invoke
synchronize_rcu() to wait for a full grace period.
Yes, this function does not take counter wrap into account. But counter wrap is harmless. If the counter wraps, we have waited for more than 2 billion grace periods (and way more on a 64-bit system!), so waiting for one additional grace period should be just fine.
-
void
rcu_barrier(void)¶ Wait until all in-flight
call_rcu()callbacks complete.
Parameters
void- no arguments
Description
Note that this primitive does not necessarily wait for an RCU grace period
to complete. For example, if there are no RCU callbacks queued anywhere
in the system, then rcu_barrier() is within its rights to return
immediately, without waiting for anything, much less an RCU grace period.
-
void
synchronize_rcu_expedited(void)¶ Brute-force RCU grace period
Parameters
void- no arguments
Description
Wait for an RCU grace period, but expedite it. The basic idea is to
IPI all non-idle non-nohz online CPUs. The IPI handler checks whether
the CPU is in an RCU critical section, and if so, it sets a flag that
causes the outermost rcu_read_unlock() to report the quiescent state
for RCU-preempt or asks the scheduler for help for RCU-sched. On the
other hand, if the CPU is not in an RCU read-side critical section,
the IPI handler reports the quiescent state immediately.
Although this is a great improvement over previous expedited
implementations, it is still unfriendly to real-time workloads, so is
thus not recommended for any sort of common-case code. In fact, if
you are using synchronize_rcu_expedited() in a loop, please restructure
your code to batch your updates, and then use a single synchronize_rcu()
instead.
This has the same semantics as (but is more brutal than) synchronize_rcu().
-
bool
rcu_read_lock_held_common(bool *ret)¶ might we be in RCU-sched read-side critical section?
Parameters
bool *ret- Best guess answer if lockdep cannot be relied on
Description
Returns true if lockdep must be ignored, in which case *ret contains
the best guess described below. Otherwise returns false, in which
case *ret tells the caller nothing and the caller should instead
consult lockdep.
If CONFIG_DEBUG_LOCK_ALLOC is selected, set *ret to nonzero iff in an
RCU-sched read-side critical section. In absence of
CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
critical section unless it can prove otherwise. Note that disabling
of preemption (including disabling irqs) counts as an RCU-sched
read-side critical section. This is useful for debug checks in functions
that required that they be called within an RCU-sched read-side
critical section.
Check debug_lockdep_rcu_enabled() to prevent false positives during boot and while lockdep is disabled.
Note that if the CPU is in the idle loop from an RCU point of view (ie:
that we are in the section between rcu_idle_enter() and rcu_idle_exit())
then rcu_read_lock_held() sets *ret to false even if the CPU did an
rcu_read_lock(). The reason for this is that RCU ignores CPUs that are
in such a section, considering these as in extended quiescent state,
so such a CPU is effectively never in an RCU read-side critical section
regardless of what RCU primitives it invokes. This state of affairs is
required — we need to keep an RCU-free window in idle where the CPU may
possibly enter into low power mode. This way we can notice an extended
quiescent state to other CPUs that started a grace period. Otherwise
we would delay any grace period as long as we run in the idle task.
Similarly, we avoid claiming an RCU read lock held if the current CPU is offline.
-
void
rcu_expedite_gp(void)¶ Expedite future RCU grace periods
Parameters
void- no arguments
Description
After a call to this function, future calls to synchronize_rcu() and
friends act as the corresponding synchronize_rcu_expedited() function
had instead been called.
-
void
rcu_unexpedite_gp(void)¶ Cancel prior
rcu_expedite_gp()invocation
Parameters
void- no arguments
Description
Undo a prior call to rcu_expedite_gp(). If all prior calls to
rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(),
and if the rcu_expedited sysfs/boot parameter is not set, then all
subsequent calls to synchronize_rcu() and friends will return to
their normal non-expedited behavior.
-
int
rcu_read_lock_held(void)¶ might we be in RCU read-side critical section?
Parameters
void- no arguments
Description
If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU read-side critical section unless it can prove otherwise. This is useful for debug checks in functions that require that they be called within an RCU read-side critical section.
Checks debug_lockdep_rcu_enabled() to prevent false positives during boot and while lockdep is disabled.
Note that rcu_read_lock() and the matching rcu_read_unlock() must
occur in the same context, for example, it is illegal to invoke
rcu_read_unlock() in process context if the matching rcu_read_lock()
was invoked from within an irq handler.
Note that rcu_read_lock() is disallowed if the CPU is either idle or
offline from an RCU perspective, so check for those as well.
-
int
rcu_read_lock_bh_held(void)¶ might we be in RCU-bh read-side critical section?
Parameters
void- no arguments
Description
Check for bottom half being disabled, which covers both the
CONFIG_PROVE_RCU and not cases. Note that if someone uses
rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
will show the situation. This is useful for debug checks in functions
that require that they be called within an RCU read-side critical
section.
Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
Note that rcu_read_lock_bh() is disallowed if the CPU is either idle or
offline from an RCU perspective, so check for those as well.
-
void
wakeme_after_rcu(struct rcu_head *head)¶ Callback function to awaken a task after grace period
Parameters
struct rcu_head *head- Pointer to rcu_head member within rcu_synchronize structure
Description
Awaken the corresponding task now that a grace period has elapsed.
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void
init_rcu_head_on_stack(struct rcu_head *head)¶ initialize on-stack rcu_head for debugobjects
Parameters
struct rcu_head *head- pointer to rcu_head structure to be initialized
Description
This function informs debugobjects of a new rcu_head structure that has been allocated as an auto variable on the stack. This function is not required for rcu_head structures that are statically defined or that are dynamically allocated on the heap. This function has no effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
-
void
destroy_rcu_head_on_stack(struct rcu_head *head)¶ destroy on-stack rcu_head for debugobjects
Parameters
struct rcu_head *head- pointer to rcu_head structure to be initialized
Description
This function informs debugobjects that an on-stack rcu_head structure
is about to go out of scope. As with init_rcu_head_on_stack(), this
function is not required for rcu_head structures that are statically
defined or that are dynamically allocated on the heap. Also as with
init_rcu_head_on_stack(), this function has no effect for
!CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
-
int
srcu_read_lock_held(const struct srcu_struct *ssp)¶ might we be in SRCU read-side critical section?
Parameters
const struct srcu_struct *ssp- The srcu_struct structure to check
Description
If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an SRCU read-side critical section unless it can prove otherwise.
Checks debug_lockdep_rcu_enabled() to prevent false positives during boot and while lockdep is disabled.
Note that SRCU is based on its own statemachine and it doesn’t relies on normal RCU, it can be called from the CPU which is in the idle loop from an RCU point of view or offline.
-
srcu_dereference_check(p, ssp, c)¶ fetch SRCU-protected pointer for later dereferencing
Parameters
p- the pointer to fetch and protect for later dereferencing
ssp- pointer to the srcu_struct, which is used to check that we really are in an SRCU read-side critical section.
c- condition to check for update-side use
Description
If PROVE_RCU is enabled, invoking this outside of an RCU read-side critical section will result in an RCU-lockdep splat, unless c evaluates to 1. The c argument will normally be a logical expression containing lockdep_is_held() calls.
-
srcu_dereference(p, ssp)¶ fetch SRCU-protected pointer for later dereferencing
Parameters
p- the pointer to fetch and protect for later dereferencing
ssp- pointer to the srcu_struct, which is used to check that we really are in an SRCU read-side critical section.
Description
Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
is enabled, invoking this outside of an RCU read-side critical
section will result in an RCU-lockdep splat.
-
srcu_dereference_notrace(p, ssp)¶ no tracing and no lockdep calls from here
Parameters
p- the pointer to fetch and protect for later dereferencing
ssp- pointer to the srcu_struct, which is used to check that we really are in an SRCU read-side critical section.
-
int
srcu_read_lock(struct srcu_struct *ssp)¶ register a new reader for an SRCU-protected structure.
Parameters
struct srcu_struct *ssp- srcu_struct in which to register the new reader.
Description
Enter an SRCU read-side critical section. Note that SRCU read-side
critical sections may be nested. However, it is illegal to
call anything that waits on an SRCU grace period for the same
srcu_struct, whether directly or indirectly. Please note that
one way to indirectly wait on an SRCU grace period is to acquire
a mutex that is held elsewhere while calling synchronize_srcu() or
synchronize_srcu_expedited().
Note that srcu_read_lock() and the matching srcu_read_unlock() must
occur in the same context, for example, it is illegal to invoke
srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
was invoked in process context.
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void
srcu_read_unlock(struct srcu_struct *ssp, int idx)¶ unregister a old reader from an SRCU-protected structure.
Parameters
struct srcu_struct *ssp- srcu_struct in which to unregister the old reader.
int idx- return value from corresponding
srcu_read_lock().
Description
Exit an SRCU read-side critical section.
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void
smp_mb__after_srcu_read_unlock(void)¶ ensure full ordering after srcu_read_unlock
Parameters
void- no arguments
Description
Converts the preceding srcu_read_unlock into a two-way memory barrier.
Call this after srcu_read_unlock, to guarantee that all memory operations that occur after smp_mb__after_srcu_read_unlock will appear to happen after the preceding srcu_read_unlock.
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int
init_srcu_struct(struct srcu_struct *ssp)¶ initialize a sleep-RCU structure
Parameters
struct srcu_struct *ssp- structure to initialize.
Description
Must invoke this on a given srcu_struct before passing that srcu_struct to any other function. Each srcu_struct represents a separate domain of SRCU protection.
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bool
srcu_readers_active(struct srcu_struct *ssp)¶ returns true if there are readers. and false otherwise
Parameters
struct srcu_struct *ssp- which srcu_struct to count active readers (holding srcu_read_lock).
Description
Note that this is not an atomic primitive, and can therefore suffer severe errors when invoked on an active srcu_struct. That said, it can be useful as an error check at cleanup time.
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void
cleanup_srcu_struct(struct srcu_struct *ssp)¶ deconstruct a sleep-RCU structure
Parameters
struct srcu_struct *ssp- structure to clean up.
Description
Must invoke this after you are finished using a given srcu_struct that
was initialized via init_srcu_struct(), else you leak memory.
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void
call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, rcu_callback_t func)¶ Queue a callback for invocation after an SRCU grace period
Parameters
struct srcu_struct *ssp- srcu_struct in queue the callback
struct rcu_head *rhp- structure to be used for queueing the SRCU callback.
rcu_callback_t func- function to be invoked after the SRCU grace period
Description
The callback function will be invoked some time after a full SRCU
grace period elapses, in other words after all pre-existing SRCU
read-side critical sections have completed. However, the callback
function might well execute concurrently with other SRCU read-side
critical sections that started after call_srcu() was invoked. SRCU
read-side critical sections are delimited by srcu_read_lock() and
srcu_read_unlock(), and may be nested.
The callback will be invoked from process context, but must nevertheless be fast and must not block.
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void
synchronize_srcu_expedited(struct srcu_struct *ssp)¶ Brute-force SRCU grace period
Parameters
struct srcu_struct *ssp- srcu_struct with which to synchronize.
Description
Wait for an SRCU grace period to elapse, but be more aggressive about spinning rather than blocking when waiting.
Note that synchronize_srcu_expedited() has the same deadlock and
memory-ordering properties as does synchronize_srcu().
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void
synchronize_srcu(struct srcu_struct *ssp)¶ wait for prior SRCU read-side critical-section completion
Parameters
struct srcu_struct *ssp- srcu_struct with which to synchronize.
Description
Wait for the count to drain to zero of both indexes. To avoid the
possible starvation of synchronize_srcu(), it waits for the count of
the index=((->srcu_idx & 1) ^ 1) to drain to zero at first,
and then flip the srcu_idx and wait for the count of the other index.
Can block; must be called from process context.
Note that it is illegal to call synchronize_srcu() from the corresponding
SRCU read-side critical section; doing so will result in deadlock.
However, it is perfectly legal to call synchronize_srcu() on one
srcu_struct from some other srcu_struct’s read-side critical section,
as long as the resulting graph of srcu_structs is acyclic.
There are memory-ordering constraints implied by synchronize_srcu().
On systems with more than one CPU, when synchronize_srcu() returns,
each CPU is guaranteed to have executed a full memory barrier since
the end of its last corresponding SRCU read-side critical section
whose beginning preceded the call to synchronize_srcu(). In addition,
each CPU having an SRCU read-side critical section that extends beyond
the return from synchronize_srcu() is guaranteed to have executed a
full memory barrier after the beginning of synchronize_srcu() and before
the beginning of that SRCU read-side critical section. Note that these
guarantees include CPUs that are offline, idle, or executing in user mode,
as well as CPUs that are executing in the kernel.
Furthermore, if CPU A invoked synchronize_srcu(), which returned
to its caller on CPU B, then both CPU A and CPU B are guaranteed
to have executed a full memory barrier during the execution of
synchronize_srcu(). This guarantee applies even if CPU A and CPU B
are the same CPU, but again only if the system has more than one CPU.
Of course, these memory-ordering guarantees apply only when
synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
passed the same srcu_struct structure.
If SRCU is likely idle, expedite the first request. This semantic was provided by Classic SRCU, and is relied upon by its users, so TREE SRCU must also provide it. Note that detecting idleness is heuristic and subject to both false positives and negatives.
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void
srcu_barrier(struct srcu_struct *ssp)¶ Wait until all in-flight
call_srcu()callbacks complete.
Parameters
struct srcu_struct *ssp- srcu_struct on which to wait for in-flight callbacks.
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unsigned long
srcu_batches_completed(struct srcu_struct *ssp)¶ return batches completed.
Parameters
struct srcu_struct *ssp- srcu_struct on which to report batch completion.
Description
Report the number of batches, correlated with, but not necessarily precisely the same as, the number of grace periods that have elapsed.
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void
hlist_bl_del_rcu(struct hlist_bl_node *n)¶ deletes entry from hash list without re-initialization
Parameters
struct hlist_bl_node *n- the element to delete from the hash list.
Note
hlist_bl_unhashed() on entry does not return true after this, the entry is in an undefined state. It is useful for RCU based lockfree traversal.
Description
In particular, it means that we can not poison the forward pointers that may still be used for walking the hash list.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_bl_add_head_rcu()
or hlist_bl_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_bl_for_each_entry().
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void
hlist_bl_add_head_rcu(struct hlist_bl_node *n, struct hlist_bl_head *h)¶
Parameters
struct hlist_bl_node *n- the element to add to the hash list.
struct hlist_bl_head *h- the list to add to.
Description
Adds the specified element to the specified hlist_bl, while permitting racing traversals.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_bl_add_head_rcu()
or hlist_bl_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_bl_for_each_entry_rcu(), used to prevent memory-consistency
problems on Alpha CPUs. Regardless of the type of CPU, the
list-traversal primitive must be guarded by rcu_read_lock().
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hlist_bl_for_each_entry_rcu(tpos, pos, head, member)¶ iterate over rcu list of given type
Parameters
tpos- the type * to use as a loop cursor.
pos- the
struct hlist_bl_nodeto use as a loop cursor. head- the head for your list.
member- the name of the hlist_bl_node within the struct.
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list_tail_rcu(head)¶ returns the prev pointer of the head of the list
Parameters
head- the head of the list
Note
This should only be used with the list header, and even then
only if list_del() and similar primitives are not also used on the
list header.
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void
list_add_rcu(struct list_head *new, struct list_head *head)¶ add a new entry to rcu-protected list
Parameters
struct list_head *new- new entry to be added
struct list_head *head- list head to add it after
Description
Insert a new entry after the specified head. This is good for implementing stacks.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as list_add_rcu()
or list_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
list_for_each_entry_rcu().
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void
list_add_tail_rcu(struct list_head *new, struct list_head *head)¶ add a new entry to rcu-protected list
Parameters
struct list_head *new- new entry to be added
struct list_head *head- list head to add it before
Description
Insert a new entry before the specified head. This is useful for implementing queues.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as list_add_tail_rcu()
or list_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
list_for_each_entry_rcu().
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void
list_del_rcu(struct list_head *entry)¶ deletes entry from list without re-initialization
Parameters
struct list_head *entry- the element to delete from the list.
Note
list_empty() on entry does not return true after this,
the entry is in an undefined state. It is useful for RCU based
lockfree traversal.
Description
In particular, it means that we can not poison the forward pointers that may still be used for walking the list.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as list_del_rcu()
or list_add_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
list_for_each_entry_rcu().
Note that the caller is not permitted to immediately free
the newly deleted entry. Instead, either synchronize_rcu()
or call_rcu() must be used to defer freeing until an RCU
grace period has elapsed.
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void
hlist_del_init_rcu(struct hlist_node *n)¶ deletes entry from hash list with re-initialization
Parameters
struct hlist_node *n- the element to delete from the hash list.
Note
list_unhashed() on the node return true after this. It is useful for RCU based read lockfree traversal if the writer side must know if the list entry is still hashed or already unhashed.
Description
In particular, it means that we can not poison the forward pointers that may still be used for walking the hash list and we can only zero the pprev pointer so list_unhashed() will return true after this.
The caller must take whatever precautions are necessary (such as
holding appropriate locks) to avoid racing with another
list-mutation primitive, such as hlist_add_head_rcu() or
hlist_del_rcu(), running on this same list. However, it is
perfectly legal to run concurrently with the _rcu list-traversal
primitives, such as hlist_for_each_entry_rcu().
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void
list_replace_rcu(struct list_head *old, struct list_head *new)¶ replace old entry by new one
Parameters
struct list_head *old- the element to be replaced
struct list_head *new- the new element to insert
Description
The old entry will be replaced with the new entry atomically.
Note
old should not be empty.
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void
__list_splice_init_rcu(struct list_head *list, struct list_head *prev, struct list_head *next, void (*sync)(void))¶ join an RCU-protected list into an existing list.
Parameters
struct list_head *list- the RCU-protected list to splice
struct list_head *prev- points to the last element of the existing list
struct list_head *next- points to the first element of the existing list
void (*sync)(void)- synchronize_rcu, synchronize_rcu_expedited, …
Description
The list pointed to by prev and next can be RCU-read traversed concurrently with this function.
Note that this function blocks.
Important note: the caller must take whatever action is necessary to prevent
any other updates to the existing list. In principle, it is possible to
modify the list as soon as sync() begins execution. If this sort of thing
becomes necessary, an alternative version based on call_rcu() could be
created. But only if -really- needed – there is no shortage of RCU API
members.
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void
list_splice_init_rcu(struct list_head *list, struct list_head *head, void (*sync)(void))¶ splice an RCU-protected list into an existing list, designed for stacks.
Parameters
struct list_head *list- the RCU-protected list to splice
struct list_head *head- the place in the existing list to splice the first list into
void (*sync)(void)- synchronize_rcu, synchronize_rcu_expedited, …
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void
list_splice_tail_init_rcu(struct list_head *list, struct list_head *head, void (*sync)(void))¶ splice an RCU-protected list into an existing list, designed for queues.
Parameters
struct list_head *list- the RCU-protected list to splice
struct list_head *head- the place in the existing list to splice the first list into
void (*sync)(void)- synchronize_rcu, synchronize_rcu_expedited, …
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list_entry_rcu(ptr, type, member)¶ get the struct for this entry
Parameters
ptr- the
struct list_headpointer. type- the type of the struct this is embedded in.
member- the name of the list_head within the struct.
Description
This primitive may safely run concurrently with the _rcu list-mutation
primitives such as list_add_rcu() as long as it’s guarded by rcu_read_lock().
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list_first_or_null_rcu(ptr, type, member)¶ get the first element from a list
Parameters
ptr- the list head to take the element from.
type- the type of the struct this is embedded in.
member- the name of the list_head within the struct.
Description
Note that if the list is empty, it returns NULL.
This primitive may safely run concurrently with the _rcu list-mutation
primitives such as list_add_rcu() as long as it’s guarded by rcu_read_lock().
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list_next_or_null_rcu(head, ptr, type, member)¶ get the first element from a list
Parameters
head- the head for the list.
ptr- the list head to take the next element from.
type- the type of the struct this is embedded in.
member- the name of the list_head within the struct.
Description
Note that if the ptr is at the end of the list, NULL is returned.
This primitive may safely run concurrently with the _rcu list-mutation
primitives such as list_add_rcu() as long as it’s guarded by rcu_read_lock().
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list_for_each_entry_rcu(pos, head, member, cond…)¶ iterate over rcu list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
cond...- optional lockdep expression if called from non-RCU protection.
Description
This list-traversal primitive may safely run concurrently with
the _rcu list-mutation primitives such as list_add_rcu()
as long as the traversal is guarded by rcu_read_lock().
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list_for_each_entry_srcu(pos, head, member, cond)¶ iterate over rcu list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
cond- lockdep expression for the lock required to traverse the list.
Description
This list-traversal primitive may safely run concurrently with
the _rcu list-mutation primitives such as list_add_rcu()
as long as the traversal is guarded by srcu_read_lock().
The lockdep expression srcu_read_lock_held() can be passed as the
cond argument from read side.
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list_entry_lockless(ptr, type, member)¶ get the struct for this entry
Parameters
ptr- the
struct list_headpointer. type- the type of the struct this is embedded in.
member- the name of the list_head within the struct.
Description
This primitive may safely run concurrently with the _rcu
list-mutation primitives such as list_add_rcu(), but requires some
implicit RCU read-side guarding. One example is running within a special
exception-time environment where preemption is disabled and where lockdep
cannot be invoked. Another example is when items are added to the list,
but never deleted.
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list_for_each_entry_lockless(pos, head, member)¶ iterate over rcu list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_struct within the struct.
Description
This primitive may safely run concurrently with the _rcu
list-mutation primitives such as list_add_rcu(), but requires some
implicit RCU read-side guarding. One example is running within a special
exception-time environment where preemption is disabled and where lockdep
cannot be invoked. Another example is when items are added to the list,
but never deleted.
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list_for_each_entry_continue_rcu(pos, head, member)¶ continue iteration over list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_head within the struct.
Description
Continue to iterate over list of given type, continuing after the current position which must have been in the list when the RCU read lock was taken. This would typically require either that you obtained the node from a previous walk of the list in the same RCU read-side critical section, or that you held some sort of non-RCU reference (such as a reference count) to keep the node alive and in the list.
This iterator is similar to list_for_each_entry_from_rcu() except
this starts after the given position and that one starts at the given
position.
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list_for_each_entry_from_rcu(pos, head, member)¶ iterate over a list from current point
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the list_node within the struct.
Description
Iterate over the tail of a list starting from a given position, which must have been in the list when the RCU read lock was taken. This would typically require either that you obtained the node from a previous walk of the list in the same RCU read-side critical section, or that you held some sort of non-RCU reference (such as a reference count) to keep the node alive and in the list.
This iterator is similar to list_for_each_entry_continue_rcu() except
this starts from the given position and that one starts from the position
after the given position.
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void
hlist_del_rcu(struct hlist_node *n)¶ deletes entry from hash list without re-initialization
Parameters
struct hlist_node *n- the element to delete from the hash list.
Note
list_unhashed() on entry does not return true after this, the entry is in an undefined state. It is useful for RCU based lockfree traversal.
Description
In particular, it means that we can not poison the forward pointers that may still be used for walking the hash list.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_add_head_rcu()
or hlist_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_for_each_entry().
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void
hlist_replace_rcu(struct hlist_node *old, struct hlist_node *new)¶ replace old entry by new one
Parameters
struct hlist_node *old- the element to be replaced
struct hlist_node *new- the new element to insert
Description
The old entry will be replaced with the new entry atomically.
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void
hlists_swap_heads_rcu(struct hlist_head *left, struct hlist_head *right)¶ swap the lists the hlist heads point to
Parameters
struct hlist_head *left- The hlist head on the left
struct hlist_head *right- The hlist head on the right
Description
- The lists start out as [left ][node1 … ] and
- [right ][node2 … ]
- The lists end up as [left ][node2 … ]
- [right ][node1 … ]
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void
hlist_add_head_rcu(struct hlist_node *n, struct hlist_head *h)¶
Parameters
struct hlist_node *n- the element to add to the hash list.
struct hlist_head *h- the list to add to.
Description
Adds the specified element to the specified hlist, while permitting racing traversals.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_add_head_rcu()
or hlist_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_for_each_entry_rcu(), used to prevent memory-consistency
problems on Alpha CPUs. Regardless of the type of CPU, the
list-traversal primitive must be guarded by rcu_read_lock().
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void
hlist_add_tail_rcu(struct hlist_node *n, struct hlist_head *h)¶
Parameters
struct hlist_node *n- the element to add to the hash list.
struct hlist_head *h- the list to add to.
Description
Adds the specified element to the specified hlist, while permitting racing traversals.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_add_head_rcu()
or hlist_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_for_each_entry_rcu(), used to prevent memory-consistency
problems on Alpha CPUs. Regardless of the type of CPU, the
list-traversal primitive must be guarded by rcu_read_lock().
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void
hlist_add_before_rcu(struct hlist_node *n, struct hlist_node *next)¶
Parameters
struct hlist_node *n- the new element to add to the hash list.
struct hlist_node *next- the existing element to add the new element before.
Description
Adds the specified element to the specified hlist before the specified node while permitting racing traversals.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_add_head_rcu()
or hlist_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_for_each_entry_rcu(), used to prevent memory-consistency
problems on Alpha CPUs.
-
void
hlist_add_behind_rcu(struct hlist_node *n, struct hlist_node *prev)¶
Parameters
struct hlist_node *n- the new element to add to the hash list.
struct hlist_node *prev- the existing element to add the new element after.
Description
Adds the specified element to the specified hlist after the specified node while permitting racing traversals.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_add_head_rcu()
or hlist_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_for_each_entry_rcu(), used to prevent memory-consistency
problems on Alpha CPUs.
-
hlist_for_each_entry_rcu(pos, head, member, cond…)¶ iterate over rcu list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the hlist_node within the struct.
cond...- optional lockdep expression if called from non-RCU protection.
Description
This list-traversal primitive may safely run concurrently with
the _rcu list-mutation primitives such as hlist_add_head_rcu()
as long as the traversal is guarded by rcu_read_lock().
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hlist_for_each_entry_srcu(pos, head, member, cond)¶ iterate over rcu list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the hlist_node within the struct.
cond- lockdep expression for the lock required to traverse the list.
Description
This list-traversal primitive may safely run concurrently with
the _rcu list-mutation primitives such as hlist_add_head_rcu()
as long as the traversal is guarded by srcu_read_lock().
The lockdep expression srcu_read_lock_held() can be passed as the
cond argument from read side.
-
hlist_for_each_entry_rcu_notrace(pos, head, member)¶ iterate over rcu list of given type (for tracing)
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the hlist_node within the struct.
Description
This list-traversal primitive may safely run concurrently with
the _rcu list-mutation primitives such as hlist_add_head_rcu()
as long as the traversal is guarded by rcu_read_lock().
This is the same as hlist_for_each_entry_rcu() except that it does
not do any RCU debugging or tracing.
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hlist_for_each_entry_rcu_bh(pos, head, member)¶ iterate over rcu list of given type
Parameters
pos- the type * to use as a loop cursor.
head- the head for your list.
member- the name of the hlist_node within the struct.
Description
This list-traversal primitive may safely run concurrently with
the _rcu list-mutation primitives such as hlist_add_head_rcu()
as long as the traversal is guarded by rcu_read_lock().
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hlist_for_each_entry_continue_rcu(pos, member)¶ iterate over a hlist continuing after current point
Parameters
pos- the type * to use as a loop cursor.
member- the name of the hlist_node within the struct.
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hlist_for_each_entry_continue_rcu_bh(pos, member)¶ iterate over a hlist continuing after current point
Parameters
pos- the type * to use as a loop cursor.
member- the name of the hlist_node within the struct.
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hlist_for_each_entry_from_rcu(pos, member)¶ iterate over a hlist continuing from current point
Parameters
pos- the type * to use as a loop cursor.
member- the name of the hlist_node within the struct.
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void
hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)¶ deletes entry from hash list with re-initialization
Parameters
struct hlist_nulls_node *n- the element to delete from the hash list.
Note
hlist_nulls_unhashed() on the node return true after this. It is useful for RCU based read lockfree traversal if the writer side must know if the list entry is still hashed or already unhashed.
Description
In particular, it means that we can not poison the forward pointers that may still be used for walking the hash list and we can only zero the pprev pointer so list_unhashed() will return true after this.
The caller must take whatever precautions are necessary (such as
holding appropriate locks) to avoid racing with another
list-mutation primitive, such as hlist_nulls_add_head_rcu() or
hlist_nulls_del_rcu(), running on this same list. However, it is
perfectly legal to run concurrently with the _rcu list-traversal
primitives, such as hlist_nulls_for_each_entry_rcu().
-
hlist_nulls_first_rcu(head)¶ returns the first element of the hash list.
Parameters
head- the head of the list.
-
hlist_nulls_next_rcu(node)¶ returns the element of the list after node.
Parameters
node- element of the list.
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void
hlist_nulls_del_rcu(struct hlist_nulls_node *n)¶ deletes entry from hash list without re-initialization
Parameters
struct hlist_nulls_node *n- the element to delete from the hash list.
Note
hlist_nulls_unhashed() on entry does not return true after this, the entry is in an undefined state. It is useful for RCU based lockfree traversal.
Description
In particular, it means that we can not poison the forward pointers that may still be used for walking the hash list.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
or hlist_nulls_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_nulls_for_each_entry().
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void
hlist_nulls_add_head_rcu(struct hlist_nulls_node *n, struct hlist_nulls_head *h)¶
Parameters
struct hlist_nulls_node *n- the element to add to the hash list.
struct hlist_nulls_head *h- the list to add to.
Description
Adds the specified element to the specified hlist_nulls, while permitting racing traversals.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
or hlist_nulls_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
problems on Alpha CPUs. Regardless of the type of CPU, the
list-traversal primitive must be guarded by rcu_read_lock().
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void
hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n, struct hlist_nulls_head *h)¶
Parameters
struct hlist_nulls_node *n- the element to add to the hash list.
struct hlist_nulls_head *h- the list to add to.
Description
Adds the specified element to the specified hlist_nulls, while permitting racing traversals.
The caller must take whatever precautions are necessary
(such as holding appropriate locks) to avoid racing
with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
or hlist_nulls_del_rcu(), running on this same list.
However, it is perfectly legal to run concurrently with
the _rcu list-traversal primitives, such as
hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
problems on Alpha CPUs. Regardless of the type of CPU, the
list-traversal primitive must be guarded by rcu_read_lock().
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hlist_nulls_for_each_entry_rcu(tpos, pos, head, member)¶ iterate over rcu list of given type
Parameters
tpos- the type * to use as a loop cursor.
pos- the
struct hlist_nulls_nodeto use as a loop cursor. head- the head of the list.
member- the name of the hlist_nulls_node within the struct.
Description
The barrier() is needed to make sure compiler doesn’t cache first element [1], as this loop can be restarted [2] [1] Documentation/core-api/atomic_ops.rst around line 114 [2] Using RCU hlist_nulls to protect list and objects around line 146
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hlist_nulls_for_each_entry_safe(tpos, pos, head, member)¶ iterate over list of given type safe against removal of list entry
Parameters
tpos- the type * to use as a loop cursor.
pos- the
struct hlist_nulls_nodeto use as a loop cursor. head- the head of the list.
member- the name of the hlist_nulls_node within the struct.
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bool
rcu_sync_is_idle(struct rcu_sync *rsp)¶ Are readers permitted to use their fastpaths?
Parameters
struct rcu_sync *rsp- Pointer to rcu_sync structure to use for synchronization
Description
Returns true if readers are permitted to use their fastpaths. Must be invoked within some flavor of RCU read-side critical section.
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void
rcu_sync_init(struct rcu_sync *rsp)¶ Initialize an rcu_sync structure
Parameters
struct rcu_sync *rsp- Pointer to rcu_sync structure to be initialized
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void
rcu_sync_enter_start(struct rcu_sync *rsp)¶ Force readers onto slow path for multiple updates
Parameters
struct rcu_sync *rsp- Pointer to rcu_sync structure to use for synchronization
Description
Must be called after rcu_sync_init() and before first use.
Ensures rcu_sync_is_idle() returns false and rcu_sync_{enter,exit}()
pairs turn into NO-OPs.
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void
rcu_sync_func(struct rcu_head *rhp)¶ Callback function managing reader access to fastpath
Parameters
struct rcu_head *rhp- Pointer to rcu_head in rcu_sync structure to use for synchronization
Description
This function is passed to call_rcu() function by rcu_sync_enter() and
rcu_sync_exit(), so that it is invoked after a grace period following the
that invocation of enter/exit.
If it is called by rcu_sync_enter() it signals that all the readers were
switched onto slow path.
If it is called by rcu_sync_exit() it takes action based on events that
have taken place in the meantime, so that closely spaced rcu_sync_enter()
and rcu_sync_exit() pairs need not wait for a grace period.
If another rcu_sync_enter() is invoked before the grace period
ended, reset state to allow the next rcu_sync_exit() to let the
readers back onto their fastpaths (after a grace period). If both
another rcu_sync_enter() and its matching rcu_sync_exit() are invoked
before the grace period ended, re-invoke call_rcu() on behalf of that
rcu_sync_exit(). Otherwise, set all state back to idle so that readers
can again use their fastpaths.
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void
rcu_sync_enter(struct rcu_sync *rsp)¶ Force readers onto slowpath
Parameters
struct rcu_sync *rsp- Pointer to rcu_sync structure to use for synchronization
Description
This function is used by updaters who need readers to make use of
a slowpath during the update. After this function returns, all
subsequent calls to rcu_sync_is_idle() will return false, which
tells readers to stay off their fastpaths. A later call to
rcu_sync_exit() re-enables reader slowpaths.
When called in isolation, rcu_sync_enter() must wait for a grace
period, however, closely spaced calls to rcu_sync_enter() can
optimize away the grace-period wait via a state machine implemented
by rcu_sync_enter(), rcu_sync_exit(), and rcu_sync_func().
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void
rcu_sync_exit(struct rcu_sync *rsp)¶ Allow readers back onto fast path after grace period
Parameters
struct rcu_sync *rsp- Pointer to rcu_sync structure to use for synchronization
Description
This function is used by updaters who have completed, and can therefore
now allow readers to make use of their fastpaths after a grace period
has elapsed. After this grace period has completed, all subsequent
calls to rcu_sync_is_idle() will return true, which tells readers that
they can once again use their fastpaths.
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void
rcu_sync_dtor(struct rcu_sync *rsp)¶ Clean up an rcu_sync structure
Parameters
struct rcu_sync *rsp- Pointer to rcu_sync structure to be cleaned up