XArray¶
| Author: | Matthew Wilcox |
|---|
Overview¶
The XArray is an abstract data type which behaves like a very large array of pointers. It meets many of the same needs as a hash or a conventional resizable array. Unlike a hash, it allows you to sensibly go to the next or previous entry in a cache-efficient manner. In contrast to a resizable array, there is no need to copy data or change MMU mappings in order to grow the array. It is more memory-efficient, parallelisable and cache friendly than a doubly-linked list. It takes advantage of RCU to perform lookups without locking.
The XArray implementation is efficient when the indices used are densely
clustered; hashing the object and using the hash as the index will not
perform well. The XArray is optimised for small indices, but still has
good performance with large indices. If your index can be larger than
ULONG_MAX then the XArray is not the data type for you. The most
important user of the XArray is the page cache.
Normal pointers may be stored in the XArray directly. They must be 4-byte
aligned, which is true for any pointer returned from kmalloc() and
alloc_page(). It isn’t true for arbitrary user-space pointers,
nor for function pointers. You can store pointers to statically allocated
objects, as long as those objects have an alignment of at least 4.
You can also store integers between 0 and LONG_MAX in the XArray.
You must first convert it into an entry using xa_mk_value().
When you retrieve an entry from the XArray, you can check whether it is
a value entry by calling xa_is_value(), and convert it back to
an integer by calling xa_to_value().
Some users want to tag the pointers they store in the XArray. You can
call xa_tag_pointer() to create an entry with a tag, xa_untag_pointer()
to turn a tagged entry back into an untagged pointer and xa_pointer_tag()
to retrieve the tag of an entry. Tagged pointers use the same bits that
are used to distinguish value entries from normal pointers, so you must
decide whether they want to store value entries or tagged pointers in
any particular XArray.
The XArray does not support storing IS_ERR() pointers as some conflict with value entries or internal entries.
An unusual feature of the XArray is the ability to create entries which
occupy a range of indices. Once stored to, looking up any index in
the range will return the same entry as looking up any other index in
the range. Storing to any index will store to all of them. Multi-index
entries can be explicitly split into smaller entries, or storing NULL
into any entry will cause the XArray to forget about the range.
Normal API¶
Start by initialising an XArray, either with DEFINE_XARRAY()
for statically allocated XArrays or xa_init() for dynamically
allocated ones. A freshly-initialised XArray contains a NULL
pointer at every index.
You can then set entries using xa_store() and get entries
using xa_load(). xa_store will overwrite any entry with the
new entry and return the previous entry stored at that index. You can
use xa_erase() instead of calling xa_store() with a
NULL entry. There is no difference between an entry that has never
been stored to, one that has been erased and one that has most recently
had NULL stored to it.
You can conditionally replace an entry at an index by using
xa_cmpxchg(). Like cmpxchg(), it will only succeed if
the entry at that index has the ‘old’ value. It also returns the entry
which was at that index; if it returns the same entry which was passed as
‘old’, then xa_cmpxchg() succeeded.
If you want to only store a new entry to an index if the current entry
at that index is NULL, you can use xa_insert() which
returns -EBUSY if the entry is not empty.
You can copy entries out of the XArray into a plain array by calling
xa_extract(). Or you can iterate over the present entries in the XArray
by calling xa_for_each(), xa_for_each_start() or xa_for_each_range().
You may prefer to use xa_find() or xa_find_after() to move to the next
present entry in the XArray.
Calling xa_store_range() stores the same entry in a range
of indices. If you do this, some of the other operations will behave
in a slightly odd way. For example, marking the entry at one index
may result in the entry being marked at some, but not all of the other
indices. Storing into one index may result in the entry retrieved by
some, but not all of the other indices changing.
Sometimes you need to ensure that a subsequent call to xa_store()
will not need to allocate memory. The xa_reserve() function
will store a reserved entry at the indicated index. Users of the
normal API will see this entry as containing NULL. If you do
not need to use the reserved entry, you can call xa_release()
to remove the unused entry. If another user has stored to the entry
in the meantime, xa_release() will do nothing; if instead you
want the entry to become NULL, you should use xa_erase().
Using xa_insert() on a reserved entry will fail.
If all entries in the array are NULL, the xa_empty() function
will return true.
Finally, you can remove all entries from an XArray by calling
xa_destroy(). If the XArray entries are pointers, you may wish
to free the entries first. You can do this by iterating over all present
entries in the XArray using the xa_for_each() iterator.
Search Marks¶
Each entry in the array has three bits associated with it called marks.
Each mark may be set or cleared independently of the others. You can
iterate over marked entries by using the xa_for_each_marked() iterator.
You can enquire whether a mark is set on an entry by using
xa_get_mark(). If the entry is not NULL, you can set a mark on it
by using xa_set_mark() and remove the mark from an entry by calling
xa_clear_mark(). You can ask whether any entry in the XArray has a
particular mark set by calling xa_marked(). Erasing an entry from the
XArray causes all marks associated with that entry to be cleared.
Setting or clearing a mark on any index of a multi-index entry will affect all indices covered by that entry. Querying the mark on any index will return the same result.
There is no way to iterate over entries which are not marked; the data
structure does not allow this to be implemented efficiently. There are
not currently iterators to search for logical combinations of bits (eg
iterate over all entries which have both XA_MARK_1 and XA_MARK_2
set, or iterate over all entries which have XA_MARK_0 or XA_MARK_2
set). It would be possible to add these if a user arises.
Allocating XArrays¶
If you use DEFINE_XARRAY_ALLOC() to define the XArray, or
initialise it by passing XA_FLAGS_ALLOC to xa_init_flags(),
the XArray changes to track whether entries are in use or not.
You can call xa_alloc() to store the entry at an unused index
in the XArray. If you need to modify the array from interrupt context,
you can use xa_alloc_bh() or xa_alloc_irq() to disable
interrupts while allocating the ID.
Using xa_store(), xa_cmpxchg() or xa_insert() will
also mark the entry as being allocated. Unlike a normal XArray, storing
NULL will mark the entry as being in use, like xa_reserve().
To free an entry, use xa_erase() (or xa_release() if
you only want to free the entry if it’s NULL).
By default, the lowest free entry is allocated starting from 0. If you
want to allocate entries starting at 1, it is more efficient to use
DEFINE_XARRAY_ALLOC1() or XA_FLAGS_ALLOC1. If you want to
allocate IDs up to a maximum, then wrap back around to the lowest free
ID, you can use xa_alloc_cyclic().
You cannot use XA_MARK_0 with an allocating XArray as this mark
is used to track whether an entry is free or not. The other marks are
available for your use.
Memory allocation¶
The xa_store(), xa_cmpxchg(), xa_alloc(),
xa_reserve() and xa_insert() functions take a gfp_t
parameter in case the XArray needs to allocate memory to store this entry.
If the entry is being deleted, no memory allocation needs to be performed,
and the GFP flags specified will be ignored.
It is possible for no memory to be allocatable, particularly if you pass
a restrictive set of GFP flags. In that case, the functions return a
special value which can be turned into an errno using xa_err().
If you don’t need to know exactly which error occurred, using
xa_is_err() is slightly more efficient.
Locking¶
When using the Normal API, you do not have to worry about locking. The XArray uses RCU and an internal spinlock to synchronise access:
- No lock needed:
- Takes RCU read lock:
- Takes xa_lock internally:
xa_store()xa_store_bh()xa_store_irq()xa_insert()xa_insert_bh()xa_insert_irq()xa_erase()xa_erase_bh()xa_erase_irq()xa_cmpxchg()xa_cmpxchg_bh()xa_cmpxchg_irq()xa_store_range()xa_alloc()xa_alloc_bh()xa_alloc_irq()xa_reserve()xa_reserve_bh()xa_reserve_irq()xa_destroy()xa_set_mark()xa_clear_mark()
- Assumes xa_lock held on entry:
If you want to take advantage of the lock to protect the data structures
that you are storing in the XArray, you can call xa_lock()
before calling xa_load(), then take a reference count on the
object you have found before calling xa_unlock(). This will
prevent stores from removing the object from the array between looking
up the object and incrementing the refcount. You can also use RCU to
avoid dereferencing freed memory, but an explanation of that is beyond
the scope of this document.
The XArray does not disable interrupts or softirqs while modifying the array. It is safe to read the XArray from interrupt or softirq context as the RCU lock provides enough protection.
If, for example, you want to store entries in the XArray in process context and then erase them in softirq context, you can do that this way:
void foo_init(struct foo *foo)
{
xa_init_flags(&foo->array, XA_FLAGS_LOCK_BH);
}
int foo_store(struct foo *foo, unsigned long index, void *entry)
{
int err;
xa_lock_bh(&foo->array);
err = xa_err(__xa_store(&foo->array, index, entry, GFP_KERNEL));
if (!err)
foo->count++;
xa_unlock_bh(&foo->array);
return err;
}
/* foo_erase() is only called from softirq context */
void foo_erase(struct foo *foo, unsigned long index)
{
xa_lock(&foo->array);
__xa_erase(&foo->array, index);
foo->count--;
xa_unlock(&foo->array);
}
If you are going to modify the XArray from interrupt or softirq context,
you need to initialise the array using xa_init_flags(), passing
XA_FLAGS_LOCK_IRQ or XA_FLAGS_LOCK_BH.
The above example also shows a common pattern of wanting to extend the coverage of the xa_lock on the store side to protect some statistics associated with the array.
Sharing the XArray with interrupt context is also possible, either
using xa_lock_irqsave() in both the interrupt handler and process
context, or xa_lock_irq() in process context and xa_lock()
in the interrupt handler. Some of the more common patterns have helper
functions such as xa_store_bh(), xa_store_irq(),
xa_erase_bh(), xa_erase_irq(), xa_cmpxchg_bh()
and xa_cmpxchg_irq().
Sometimes you need to protect access to the XArray with a mutex because
that lock sits above another mutex in the locking hierarchy. That does
not entitle you to use functions like __xa_erase() without taking
the xa_lock; the xa_lock is used for lockdep validation and will be used
for other purposes in the future.
The __xa_set_mark() and __xa_clear_mark() functions are also
available for situations where you look up an entry and want to atomically
set or clear a mark. It may be more efficient to use the advanced API
in this case, as it will save you from walking the tree twice.
Advanced API¶
The advanced API offers more flexibility and better performance at the cost of an interface which can be harder to use and has fewer safeguards. No locking is done for you by the advanced API, and you are required to use the xa_lock while modifying the array. You can choose whether to use the xa_lock or the RCU lock while doing read-only operations on the array. You can mix advanced and normal operations on the same array; indeed the normal API is implemented in terms of the advanced API. The advanced API is only available to modules with a GPL-compatible license.
The advanced API is based around the xa_state. This is an opaque data
structure which you declare on the stack using the XA_STATE()
macro. This macro initialises the xa_state ready to start walking
around the XArray. It is used as a cursor to maintain the position
in the XArray and let you compose various operations together without
having to restart from the top every time.
The xa_state is also used to store errors. You can call
xas_error() to retrieve the error. All operations check whether
the xa_state is in an error state before proceeding, so there’s no need
for you to check for an error after each call; you can make multiple
calls in succession and only check at a convenient point. The only
errors currently generated by the XArray code itself are ENOMEM and
EINVAL, but it supports arbitrary errors in case you want to call
xas_set_err() yourself.
If the xa_state is holding an ENOMEM error, calling xas_nomem()
will attempt to allocate more memory using the specified gfp flags and
cache it in the xa_state for the next attempt. The idea is that you take
the xa_lock, attempt the operation and drop the lock. The operation
attempts to allocate memory while holding the lock, but it is more
likely to fail. Once you have dropped the lock, xas_nomem()
can try harder to allocate more memory. It will return true if it
is worth retrying the operation (i.e. that there was a memory error and
more memory was allocated). If it has previously allocated memory, and
that memory wasn’t used, and there is no error (or some error that isn’t
ENOMEM), then it will free the memory previously allocated.
Internal Entries¶
The XArray reserves some entries for its own purposes. These are never
exposed through the normal API, but when using the advanced API, it’s
possible to see them. Usually the best way to handle them is to pass them
to xas_retry(), and retry the operation if it returns true.
| Name | Test | Usage |
| Node | xa_is_node() | An XArray node. May be visible when using a multi-index xa_state. |
| Sibling | xa_is_sibling() |
A non-canonical entry for a multi-index entry. The value indicates which slot in this node has the canonical entry. |
| Retry | xa_is_retry() |
This entry is currently being modified by a thread which has the xa_lock. The node containing this entry may be freed at the end of this RCU period. You should restart the lookup from the head of the array. |
| Zero | xa_is_zero() |
Zero entries appear as NULL through the Normal API, but occupy
an entry in the XArray which can be used to reserve the index for
future use. This is used by allocating XArrays for allocated entries
which are NULL. |
Other internal entries may be added in the future. As far as possible, they
will be handled by xas_retry().
Additional functionality¶
The xas_create_range() function allocates all the necessary memory
to store every entry in a range. It will set ENOMEM in the xa_state if
it cannot allocate memory.
You can use xas_init_marks() to reset the marks on an entry
to their default state. This is usually all marks clear, unless the
XArray is marked with XA_FLAGS_TRACK_FREE, in which case mark 0 is set
and all other marks are clear. Replacing one entry with another using
xas_store() will not reset the marks on that entry; if you want
the marks reset, you should do that explicitly.
The xas_load() will walk the xa_state as close to the entry
as it can. If you know the xa_state has already been walked to the
entry and need to check that the entry hasn’t changed, you can use
xas_reload() to save a function call.
If you need to move to a different index in the XArray, call
xas_set(). This resets the cursor to the top of the tree, which
will generally make the next operation walk the cursor to the desired
spot in the tree. If you want to move to the next or previous index,
call xas_next() or xas_prev(). Setting the index does
not walk the cursor around the array so does not require a lock to be
held, while moving to the next or previous index does.
You can search for the next present entry using xas_find(). This
is the equivalent of both xa_find() and xa_find_after();
if the cursor has been walked to an entry, then it will find the next
entry after the one currently referenced. If not, it will return the
entry at the index of the xa_state. Using xas_next_entry() to
move to the next present entry instead of xas_find() will save
a function call in the majority of cases at the expense of emitting more
inline code.
The xas_find_marked() function is similar. If the xa_state has
not been walked, it will return the entry at the index of the xa_state,
if it is marked. Otherwise, it will return the first marked entry after
the entry referenced by the xa_state. The xas_next_marked()
function is the equivalent of xas_next_entry().
When iterating over a range of the XArray using xas_for_each()
or xas_for_each_marked(), it may be necessary to temporarily stop
the iteration. The xas_pause() function exists for this purpose.
After you have done the necessary work and wish to resume, the xa_state
is in an appropriate state to continue the iteration after the entry
you last processed. If you have interrupts disabled while iterating,
then it is good manners to pause the iteration and reenable interrupts
every XA_CHECK_SCHED entries.
The xas_get_mark(), xas_set_mark() and xas_clear_mark() functions require
the xa_state cursor to have been moved to the appropriate location in the
XArray; they will do nothing if you have called xas_pause() or xas_set()
immediately before.
You can call xas_set_update() to have a callback function
called each time the XArray updates a node. This is used by the page
cache workingset code to maintain its list of nodes which contain only
shadow entries.
Multi-Index Entries¶
The XArray has the ability to tie multiple indices together so that operations on one index affect all indices. For example, storing into any index will change the value of the entry retrieved from any index. Setting or clearing a mark on any index will set or clear the mark on every index that is tied together. The current implementation only allows tying ranges which are aligned powers of two together; eg indices 64-127 may be tied together, but 2-6 may not be. This may save substantial quantities of memory; for example tying 512 entries together will save over 4kB.
You can create a multi-index entry by using XA_STATE_ORDER()
or xas_set_order() followed by a call to xas_store().
Calling xas_load() with a multi-index xa_state will walk the
xa_state to the right location in the tree, but the return value is not
meaningful, potentially being an internal entry or NULL even when there
is an entry stored within the range. Calling xas_find_conflict()
will return the first entry within the range or NULL if there are no
entries in the range. The xas_for_each_conflict() iterator will
iterate over every entry which overlaps the specified range.
If xas_load() encounters a multi-index entry, the xa_index
in the xa_state will not be changed. When iterating over an XArray
or calling xas_find(), if the initial index is in the middle
of a multi-index entry, it will not be altered. Subsequent calls
or iterations will move the index to the first index in the range.
Each entry will only be returned once, no matter how many indices it
occupies.
Using xas_next() or xas_prev() with a multi-index xa_state is not
supported. Using either of these functions on a multi-index entry will
reveal sibling entries; these should be skipped over by the caller.
Storing NULL into any index of a multi-index entry will set the
entry at every index to NULL and dissolve the tie. A multi-index
entry can be split into entries occupying smaller ranges by calling
xas_split_alloc() without the xa_lock held, followed by taking the lock
and calling xas_split().
Functions and structures¶
-
void *
xa_mk_value(unsigned long v)¶ Create an XArray entry from an integer.
Parameters
unsigned long v- Value to store in XArray.
Context
Any context.
Return
An entry suitable for storing in the XArray.
-
unsigned long
xa_to_value(const void *entry)¶ Get value stored in an XArray entry.
Parameters
const void *entry- XArray entry.
Context
Any context.
Return
The value stored in the XArray entry.
-
bool
xa_is_value(const void *entry)¶ Determine if an entry is a value.
Parameters
const void *entry- XArray entry.
Context
Any context.
Return
True if the entry is a value, false if it is a pointer.
-
void *
xa_tag_pointer(void *p, unsigned long tag)¶ Create an XArray entry for a tagged pointer.
Parameters
void *p- Plain pointer.
unsigned long tag- Tag value (0, 1 or 3).
Description
If the user of the XArray prefers, they can tag their pointers instead of storing value entries. Three tags are available (0, 1 and 3). These are distinct from the xa_mark_t as they are not replicated up through the array and cannot be searched for.
Context
Any context.
Return
An XArray entry.
-
void *
xa_untag_pointer(void *entry)¶ Turn an XArray entry into a plain pointer.
Parameters
void *entry- XArray entry.
Description
If you have stored a tagged pointer in the XArray, call this function to get the untagged version of the pointer.
Context
Any context.
Return
A pointer.
-
unsigned int
xa_pointer_tag(void *entry)¶ Get the tag stored in an XArray entry.
Parameters
void *entry- XArray entry.
Description
If you have stored a tagged pointer in the XArray, call this function to get the tag of that pointer.
Context
Any context.
Return
A tag.
-
bool
xa_is_zero(const void *entry)¶ Is the entry a zero entry?
Parameters
const void *entry- Entry retrieved from the XArray
Description
The normal API will return NULL as the contents of a slot containing a zero entry. You can only see zero entries by using the advanced API.
Return
true if the entry is a zero entry.
-
bool
xa_is_err(const void *entry)¶ Report whether an XArray operation returned an error
Parameters
const void *entry- Result from calling an XArray function
Description
If an XArray operation cannot complete an operation, it will return
a special value indicating an error. This function tells you
whether an error occurred; xa_err() tells you which error occurred.
Context
Any context.
Return
true if the entry indicates an error.
-
int
xa_err(void *entry)¶ Turn an XArray result into an errno.
Parameters
void *entry- Result from calling an XArray function.
Description
If an XArray operation cannot complete an operation, it will return a special pointer value which encodes an errno. This function extracts the errno from the pointer value, or returns 0 if the pointer does not represent an errno.
Context
Any context.
Return
A negative errno or 0.
-
struct
xa_limit¶ Represents a range of IDs.
Definition
struct xa_limit {
u32 max;
u32 min;
};
Members
max- The maximum ID to allocate (inclusive).
min- The lowest ID to allocate (inclusive).
Description
This structure is used either directly or via the XA_LIMIT() macro to communicate the range of IDs that are valid for allocation. Two common ranges are predefined for you: * xa_limit_32b - [0 - UINT_MAX] * xa_limit_31b - [0 - INT_MAX]
-
struct
xarray¶ The anchor of the XArray.
Definition
struct xarray {
spinlock_t xa_lock;
};
Members
xa_lock- Lock that protects the contents of the XArray.
Description
To use the xarray, define it statically or embed it in your data structure. It is a very small data structure, so it does not usually make sense to allocate it separately and keep a pointer to it in your data structure.
You may use the xa_lock to protect your own data structures as well.
-
DEFINE_XARRAY_FLAGS(name, flags)¶ Define an XArray with custom flags.
Parameters
name- A string that names your XArray.
flags- XA_FLAG values.
Description
This is intended for file scope definitions of XArrays. It declares
and initialises an empty XArray with the chosen name and flags. It is
equivalent to calling xa_init_flags() on the array, but it does the
initialisation at compiletime instead of runtime.
-
DEFINE_XARRAY(name)¶ Define an XArray.
Parameters
name- A string that names your XArray.
Description
This is intended for file scope definitions of XArrays. It declares
and initialises an empty XArray with the chosen name. It is equivalent
to calling xa_init() on the array, but it does the initialisation at
compiletime instead of runtime.
-
DEFINE_XARRAY_ALLOC(name)¶ Define an XArray which allocates IDs starting at 0.
Parameters
name- A string that names your XArray.
Description
This is intended for file scope definitions of allocating XArrays.
See also DEFINE_XARRAY().
-
DEFINE_XARRAY_ALLOC1(name)¶ Define an XArray which allocates IDs starting at 1.
Parameters
name- A string that names your XArray.
Description
This is intended for file scope definitions of allocating XArrays.
See also DEFINE_XARRAY().
Parameters
struct xarray *xa- XArray.
gfp_t flags- XA_FLAG values.
Description
If you need to initialise an XArray with special flags (eg you need
to take the lock from interrupt context), use this function instead
of xa_init().
Context
Any context.
Parameters
struct xarray *xa- XArray.
Description
An empty XArray is full of NULL entries.
Context
Any context.
Parameters
const struct xarray *xa- XArray.
Context
Any context.
Return
true if the array contains only NULL pointers.
-
bool
xa_marked(const struct xarray *xa, xa_mark_t mark)¶ Inquire whether any entry in this array has a mark set
Parameters
const struct xarray *xa- Array
xa_mark_t mark- Mark value
Context
Any context.
Return
true if any entry has this mark set.
-
xa_for_each_range(xa, index, entry, start, last)¶ Iterate over a portion of an XArray.
Parameters
xa- XArray.
index- Index of entry.
entry- Entry retrieved from array.
start- First index to retrieve from array.
last- Last index to retrieve from array.
Description
During the iteration, entry will have the value of the entry stored in xa at index. You may modify index during the iteration if you want to skip or reprocess indices. It is safe to modify the array during the iteration. At the end of the iteration, entry will be set to NULL and index will have a value less than or equal to max.
xa_for_each_range() is O(n.log(n)) while xas_for_each() is O(n). You have
to handle your own locking with xas_for_each(), and if you have to unlock
after each iteration, it will also end up being O(n.log(n)).
xa_for_each_range() will spin if it hits a retry entry; if you intend to
see retry entries, you should use the xas_for_each() iterator instead.
The xas_for_each() iterator will expand into more inline code than
xa_for_each_range().
Context
Any context. Takes and releases the RCU lock.
-
xa_for_each_start(xa, index, entry, start)¶ Iterate over a portion of an XArray.
Parameters
xa- XArray.
index- Index of entry.
entry- Entry retrieved from array.
start- First index to retrieve from array.
Description
During the iteration, entry will have the value of the entry stored in xa at index. You may modify index during the iteration if you want to skip or reprocess indices. It is safe to modify the array during the iteration. At the end of the iteration, entry will be set to NULL and index will have a value less than or equal to max.
xa_for_each_start() is O(n.log(n)) while xas_for_each() is O(n). You have
to handle your own locking with xas_for_each(), and if you have to unlock
after each iteration, it will also end up being O(n.log(n)).
xa_for_each_start() will spin if it hits a retry entry; if you intend to
see retry entries, you should use the xas_for_each() iterator instead.
The xas_for_each() iterator will expand into more inline code than
xa_for_each_start().
Context
Any context. Takes and releases the RCU lock.
-
xa_for_each(xa, index, entry)¶ Iterate over present entries in an XArray.
Parameters
xa- XArray.
index- Index of entry.
entry- Entry retrieved from array.
Description
During the iteration, entry will have the value of the entry stored in xa at index. You may modify index during the iteration if you want to skip or reprocess indices. It is safe to modify the array during the iteration. At the end of the iteration, entry will be set to NULL and index will have a value less than or equal to max.
xa_for_each() is O(n.log(n)) while xas_for_each() is O(n). You have
to handle your own locking with xas_for_each(), and if you have to unlock
after each iteration, it will also end up being O(n.log(n)). xa_for_each()
will spin if it hits a retry entry; if you intend to see retry entries,
you should use the xas_for_each() iterator instead. The xas_for_each()
iterator will expand into more inline code than xa_for_each().
Context
Any context. Takes and releases the RCU lock.
-
xa_for_each_marked(xa, index, entry, filter)¶ Iterate over marked entries in an XArray.
Parameters
xa- XArray.
index- Index of entry.
entry- Entry retrieved from array.
filter- Selection criterion.
Description
During the iteration, entry will have the value of the entry stored in xa at index. The iteration will skip all entries in the array which do not match filter. You may modify index during the iteration if you want to skip or reprocess indices. It is safe to modify the array during the iteration. At the end of the iteration, entry will be set to NULL and index will have a value less than or equal to max.
xa_for_each_marked() is O(n.log(n)) while xas_for_each_marked() is O(n).
You have to handle your own locking with xas_for_each(), and if you have
to unlock after each iteration, it will also end up being O(n.log(n)).
xa_for_each_marked() will spin if it hits a retry entry; if you intend to
see retry entries, you should use the xas_for_each_marked() iterator
instead. The xas_for_each_marked() iterator will expand into more inline
code than xa_for_each_marked().
Context
Any context. Takes and releases the RCU lock.
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void *
xa_store_bh(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)¶ Store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
This function is like calling xa_store() except it disables softirqs
while holding the array lock.
Context
Any context. Takes and releases the xa_lock while disabling softirqs.
Return
The old entry at this index or xa_err() if an error happened.
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void *
xa_store_irq(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)¶ Store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
This function is like calling xa_store() except it disables interrupts
while holding the array lock.
Context
Process context. Takes and releases the xa_lock while disabling interrupts.
Return
The old entry at this index or xa_err() if an error happened.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
Description
After this function returns, loading from index will return NULL.
If the index is part of a multi-index entry, all indices will be erased
and none of the entries will be part of a multi-index entry.
Context
Any context. Takes and releases the xa_lock while disabling softirqs.
Return
The entry which used to be at this index.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
Description
After this function returns, loading from index will return NULL.
If the index is part of a multi-index entry, all indices will be erased
and none of the entries will be part of a multi-index entry.
Context
Process context. Takes and releases the xa_lock while disabling interrupts.
Return
The entry which used to be at this index.
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void *
xa_cmpxchg(struct xarray *xa, unsigned long index, void *old, void *entry, gfp_t gfp)¶ Conditionally replace an entry in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *old- Old value to test against.
void *entry- New value to place in array.
gfp_t gfp- Memory allocation flags.
Description
If the entry at index is the same as old, replace it with entry. If the return value is equal to old, then the exchange was successful.
Context
Any context. Takes and releases the xa_lock. May sleep if the gfp flags permit.
Return
The old value at this index or xa_err() if an error happened.
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void *
xa_cmpxchg_bh(struct xarray *xa, unsigned long index, void *old, void *entry, gfp_t gfp)¶ Conditionally replace an entry in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *old- Old value to test against.
void *entry- New value to place in array.
gfp_t gfp- Memory allocation flags.
Description
This function is like calling xa_cmpxchg() except it disables softirqs
while holding the array lock.
Context
Any context. Takes and releases the xa_lock while disabling softirqs. May sleep if the gfp flags permit.
Return
The old value at this index or xa_err() if an error happened.
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void *
xa_cmpxchg_irq(struct xarray *xa, unsigned long index, void *old, void *entry, gfp_t gfp)¶ Conditionally replace an entry in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *old- Old value to test against.
void *entry- New value to place in array.
gfp_t gfp- Memory allocation flags.
Description
This function is like calling xa_cmpxchg() except it disables interrupts
while holding the array lock.
Context
Process context. Takes and releases the xa_lock while disabling interrupts. May sleep if the gfp flags permit.
Return
The old value at this index or xa_err() if an error happened.
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int
xa_insert(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)¶ Store this entry in the XArray unless another entry is already present.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
Inserting a NULL entry will store a reserved entry (like xa_reserve())
if no entry is present. Inserting will fail if a reserved entry is
present, even though loading from this index will return NULL.
Context
Any context. Takes and releases the xa_lock. May sleep if the gfp flags permit.
Return
0 if the store succeeded. -EBUSY if another entry was present. -ENOMEM if memory could not be allocated.
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int
xa_insert_bh(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)¶ Store this entry in the XArray unless another entry is already present.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
Inserting a NULL entry will store a reserved entry (like xa_reserve())
if no entry is present. Inserting will fail if a reserved entry is
present, even though loading from this index will return NULL.
Context
Any context. Takes and releases the xa_lock while disabling softirqs. May sleep if the gfp flags permit.
Return
0 if the store succeeded. -EBUSY if another entry was present. -ENOMEM if memory could not be allocated.
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int
xa_insert_irq(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)¶ Store this entry in the XArray unless another entry is already present.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
Inserting a NULL entry will store a reserved entry (like xa_reserve())
if no entry is present. Inserting will fail if a reserved entry is
present, even though loading from this index will return NULL.
Context
Process context. Takes and releases the xa_lock while disabling interrupts. May sleep if the gfp flags permit.
Return
0 if the store succeeded. -EBUSY if another entry was present. -ENOMEM if memory could not be allocated.
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int
xa_alloc(struct xarray *xa, u32 *id, void *entry, struct xa_limit limit, gfp_t gfp)¶ Find somewhere to store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
u32 *id- Pointer to ID.
void *entry- New entry.
struct xa_limit limit- Range of ID to allocate.
gfp_t gfp- Memory allocation flags.
Description
Finds an empty entry in xa between limit.min and limit.max, stores the index into the id pointer, then stores the entry at that index. A concurrent lookup will not see an uninitialised id.
Context
Any context. Takes and releases the xa_lock. May sleep if the gfp flags permit.
Return
0 on success, -ENOMEM if memory could not be allocated or -EBUSY if there are no free entries in limit.
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int
xa_alloc_bh(struct xarray *xa, u32 *id, void *entry, struct xa_limit limit, gfp_t gfp)¶ Find somewhere to store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
u32 *id- Pointer to ID.
void *entry- New entry.
struct xa_limit limit- Range of ID to allocate.
gfp_t gfp- Memory allocation flags.
Description
Finds an empty entry in xa between limit.min and limit.max, stores the index into the id pointer, then stores the entry at that index. A concurrent lookup will not see an uninitialised id.
Context
Any context. Takes and releases the xa_lock while disabling softirqs. May sleep if the gfp flags permit.
Return
0 on success, -ENOMEM if memory could not be allocated or -EBUSY if there are no free entries in limit.
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int
xa_alloc_irq(struct xarray *xa, u32 *id, void *entry, struct xa_limit limit, gfp_t gfp)¶ Find somewhere to store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
u32 *id- Pointer to ID.
void *entry- New entry.
struct xa_limit limit- Range of ID to allocate.
gfp_t gfp- Memory allocation flags.
Description
Finds an empty entry in xa between limit.min and limit.max, stores the index into the id pointer, then stores the entry at that index. A concurrent lookup will not see an uninitialised id.
Context
Process context. Takes and releases the xa_lock while disabling interrupts. May sleep if the gfp flags permit.
Return
0 on success, -ENOMEM if memory could not be allocated or -EBUSY if there are no free entries in limit.
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int
xa_alloc_cyclic(struct xarray *xa, u32 *id, void *entry, struct xa_limit limit, u32 *next, gfp_t gfp)¶ Find somewhere to store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
u32 *id- Pointer to ID.
void *entry- New entry.
struct xa_limit limit- Range of allocated ID.
u32 *next- Pointer to next ID to allocate.
gfp_t gfp- Memory allocation flags.
Description
Finds an empty entry in xa between limit.min and limit.max, stores the index into the id pointer, then stores the entry at that index. A concurrent lookup will not see an uninitialised id. The search for an empty entry will start at next and will wrap around if necessary.
Context
Any context. Takes and releases the xa_lock. May sleep if the gfp flags permit.
Return
0 if the allocation succeeded without wrapping. 1 if the allocation succeeded after wrapping, -ENOMEM if memory could not be allocated or -EBUSY if there are no free entries in limit.
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int
xa_alloc_cyclic_bh(struct xarray *xa, u32 *id, void *entry, struct xa_limit limit, u32 *next, gfp_t gfp)¶ Find somewhere to store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
u32 *id- Pointer to ID.
void *entry- New entry.
struct xa_limit limit- Range of allocated ID.
u32 *next- Pointer to next ID to allocate.
gfp_t gfp- Memory allocation flags.
Description
Finds an empty entry in xa between limit.min and limit.max, stores the index into the id pointer, then stores the entry at that index. A concurrent lookup will not see an uninitialised id. The search for an empty entry will start at next and will wrap around if necessary.
Context
Any context. Takes and releases the xa_lock while disabling softirqs. May sleep if the gfp flags permit.
Return
0 if the allocation succeeded without wrapping. 1 if the allocation succeeded after wrapping, -ENOMEM if memory could not be allocated or -EBUSY if there are no free entries in limit.
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int
xa_alloc_cyclic_irq(struct xarray *xa, u32 *id, void *entry, struct xa_limit limit, u32 *next, gfp_t gfp)¶ Find somewhere to store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
u32 *id- Pointer to ID.
void *entry- New entry.
struct xa_limit limit- Range of allocated ID.
u32 *next- Pointer to next ID to allocate.
gfp_t gfp- Memory allocation flags.
Description
Finds an empty entry in xa between limit.min and limit.max, stores the index into the id pointer, then stores the entry at that index. A concurrent lookup will not see an uninitialised id. The search for an empty entry will start at next and will wrap around if necessary.
Context
Process context. Takes and releases the xa_lock while disabling interrupts. May sleep if the gfp flags permit.
Return
0 if the allocation succeeded without wrapping. 1 if the allocation succeeded after wrapping, -ENOMEM if memory could not be allocated or -EBUSY if there are no free entries in limit.
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int
xa_reserve(struct xarray *xa, unsigned long index, gfp_t gfp)¶ Reserve this index in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
gfp_t gfp- Memory allocation flags.
Description
Ensures there is somewhere to store an entry at index in the array.
If there is already something stored at index, this function does
nothing. If there was nothing there, the entry is marked as reserved.
Loading from a reserved entry returns a NULL pointer.
If you do not use the entry that you have reserved, call xa_release()
or xa_erase() to free any unnecessary memory.
Context
Any context. Takes and releases the xa_lock. May sleep if the gfp flags permit.
Return
0 if the reservation succeeded or -ENOMEM if it failed.
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int
xa_reserve_bh(struct xarray *xa, unsigned long index, gfp_t gfp)¶ Reserve this index in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
gfp_t gfp- Memory allocation flags.
Description
A softirq-disabling version of xa_reserve().
Context
Any context. Takes and releases the xa_lock while disabling softirqs.
Return
0 if the reservation succeeded or -ENOMEM if it failed.
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int
xa_reserve_irq(struct xarray *xa, unsigned long index, gfp_t gfp)¶ Reserve this index in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
gfp_t gfp- Memory allocation flags.
Description
An interrupt-disabling version of xa_reserve().
Context
Process context. Takes and releases the xa_lock while disabling interrupts.
Return
0 if the reservation succeeded or -ENOMEM if it failed.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
Description
After calling xa_reserve(), you can call this function to release the
reservation. If the entry at index has been stored to, this function
will do nothing.
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bool
xa_is_sibling(const void *entry)¶ Is the entry a sibling entry?
Parameters
const void *entry- Entry retrieved from the XArray
Return
true if the entry is a sibling entry.
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bool
xa_is_retry(const void *entry)¶ Is the entry a retry entry?
Parameters
const void *entry- Entry retrieved from the XArray
Return
true if the entry is a retry entry.
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bool
xa_is_advanced(const void *entry)¶ Is the entry only permitted for the advanced API?
Parameters
const void *entry- Entry to be stored in the XArray.
Return
true if the entry cannot be stored by the normal API.
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xa_update_node_t¶ Typedef: A callback function from the XArray.
Syntax
void xa_update_node_t (struct xa_node *node)
Parameters
struct xa_node *node- The node which is being processed
Description
This function is called every time the XArray updates the count of present and value entries in a node. It allows advanced users to maintain the private_list in the node.
Context
The xa_lock is held and interrupts may be disabled. Implementations should not drop the xa_lock, nor re-enable interrupts.
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XA_STATE(name, array, index)¶ Declare an XArray operation state.
Parameters
name- Name of this operation state (usually xas).
array- Array to operate on.
index- Initial index of interest.
Description
Declare and initialise an xa_state on the stack.
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XA_STATE_ORDER(name, array, index, order)¶ Declare an XArray operation state.
Parameters
name- Name of this operation state (usually xas).
array- Array to operate on.
index- Initial index of interest.
order- Order of entry.
Description
Declare and initialise an xa_state on the stack. This variant of
XA_STATE() allows you to specify the ‘order’ of the element you
want to operate on.`
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int
xas_error(const struct xa_state *xas)¶ Return an errno stored in the xa_state.
Parameters
const struct xa_state *xas- XArray operation state.
Return
0 if no error has been noted. A negative errno if one has.
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void
xas_set_err(struct xa_state *xas, long err)¶ Note an error in the xa_state.
Parameters
struct xa_state *xas- XArray operation state.
long err- Negative error number.
Description
Only call this function with a negative err; zero or positive errors
will probably not behave the way you think they should. If you want
to clear the error from an xa_state, use xas_reset().
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bool
xas_invalid(const struct xa_state *xas)¶ Is the xas in a retry or error state?
Parameters
const struct xa_state *xas- XArray operation state.
Return
true if the xas cannot be used for operations.
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bool
xas_valid(const struct xa_state *xas)¶ Is the xas a valid cursor into the array?
Parameters
const struct xa_state *xas- XArray operation state.
Return
true if the xas can be used for operations.
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bool
xas_is_node(const struct xa_state *xas)¶ Does the xas point to a node?
Parameters
const struct xa_state *xas- XArray operation state.
Return
true if the xas currently references a node.
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void
xas_reset(struct xa_state *xas)¶ Reset an XArray operation state.
Parameters
struct xa_state *xas- XArray operation state.
Description
Resets the error or walk state of the xas so future walks of the array will start from the root. Use this if you have dropped the xarray lock and want to reuse the xa_state.
Context
Any context.
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bool
xas_retry(struct xa_state *xas, const void *entry)¶ Retry the operation if appropriate.
Parameters
struct xa_state *xas- XArray operation state.
const void *entry- Entry from xarray.
Description
The advanced functions may sometimes return an internal entry, such as a retry entry or a zero entry. This function sets up the xas to restart the walk from the head of the array if needed.
Context
Any context.
Return
true if the operation needs to be retried.
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void *
xas_reload(struct xa_state *xas)¶ Refetch an entry from the xarray.
Parameters
struct xa_state *xas- XArray operation state.
Description
Use this function to check that a previously loaded entry still has the same value. This is useful for the lockless pagecache lookup where we walk the array with only the RCU lock to protect us, lock the page, then check that the page hasn’t moved since we looked it up.
The caller guarantees that xas is still valid. If it may be in an
error or restart state, call xas_load() instead.
Return
The entry at this location in the xarray.
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void
xas_set(struct xa_state *xas, unsigned long index)¶ Set up XArray operation state for a different index.
Parameters
struct xa_state *xas- XArray operation state.
unsigned long index- New index into the XArray.
Description
Move the operation state to refer to a different index. This will
have the effect of starting a walk from the top; see xas_next()
to move to an adjacent index.
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void
xas_set_order(struct xa_state *xas, unsigned long index, unsigned int order)¶ Set up XArray operation state for a multislot entry.
Parameters
struct xa_state *xas- XArray operation state.
unsigned long index- Target of the operation.
unsigned int order- Entry occupies 2^**order** indices.
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void
xas_set_update(struct xa_state *xas, xa_update_node_t update)¶ Set up XArray operation state for a callback.
Parameters
struct xa_state *xas- XArray operation state.
xa_update_node_t update- Function to call when updating a node.
Description
The XArray can notify a caller after it has updated an xa_node. This is advanced functionality and is only needed by the page cache.
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void *
xas_next_entry(struct xa_state *xas, unsigned long max)¶ Advance iterator to next present entry.
Parameters
struct xa_state *xas- XArray operation state.
unsigned long max- Highest index to return.
Description
xas_next_entry() is an inline function to optimise xarray traversal for
speed. It is equivalent to calling xas_find(), and will call xas_find()
for all the hard cases.
Return
The next present entry after the one currently referred to by xas.
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void *
xas_next_marked(struct xa_state *xas, unsigned long max, xa_mark_t mark)¶ Advance iterator to next marked entry.
Parameters
struct xa_state *xas- XArray operation state.
unsigned long max- Highest index to return.
xa_mark_t mark- Mark to search for.
Description
xas_next_marked() is an inline function to optimise xarray traversal for
speed. It is equivalent to calling xas_find_marked(), and will call
xas_find_marked() for all the hard cases.
Return
The next marked entry after the one currently referred to by xas.
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xas_for_each(xas, entry, max)¶ Iterate over a range of an XArray.
Parameters
xas- XArray operation state.
entry- Entry retrieved from the array.
max- Maximum index to retrieve from array.
Description
The loop body will be executed for each entry present in the xarray
between the current xas position and max. entry will be set to
the entry retrieved from the xarray. It is safe to delete entries
from the array in the loop body. You should hold either the RCU lock
or the xa_lock while iterating. If you need to drop the lock, call
xas_pause() first.
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xas_for_each_marked(xas, entry, max, mark)¶ Iterate over a range of an XArray.
Parameters
xas- XArray operation state.
entry- Entry retrieved from the array.
max- Maximum index to retrieve from array.
mark- Mark to search for.
Description
The loop body will be executed for each marked entry in the xarray
between the current xas position and max. entry will be set to
the entry retrieved from the xarray. It is safe to delete entries
from the array in the loop body. You should hold either the RCU lock
or the xa_lock while iterating. If you need to drop the lock, call
xas_pause() first.
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xas_for_each_conflict(xas, entry)¶ Iterate over a range of an XArray.
Parameters
xas- XArray operation state.
entry- Entry retrieved from the array.
Description
The loop body will be executed for each entry in the XArray that
lies within the range specified by xas. If the loop terminates
normally, entry will be NULL. The user may break out of the loop,
which will leave entry set to the conflicting entry. The caller
may also call xa_set_err() to exit the loop while setting an error
to record the reason.
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void *
xas_prev(struct xa_state *xas)¶ Move iterator to previous index.
Parameters
struct xa_state *xas- XArray operation state.
Description
If the xas was in an error state, it will remain in an error state
and this function will return NULL. If the xas has never been walked,
it will have the effect of calling xas_load(). Otherwise one will be
subtracted from the index and the state will be walked to the correct
location in the array for the next operation.
If the iterator was referencing index 0, this function wraps
around to ULONG_MAX.
Return
The entry at the new index. This may be NULL or an internal
entry.
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void *
xas_next(struct xa_state *xas)¶ Move state to next index.
Parameters
struct xa_state *xas- XArray operation state.
Description
If the xas was in an error state, it will remain in an error state
and this function will return NULL. If the xas has never been walked,
it will have the effect of calling xas_load(). Otherwise one will be
added to the index and the state will be walked to the correct
location in the array for the next operation.
If the iterator was referencing index ULONG_MAX, this function wraps
around to 0.
Return
The entry at the new index. This may be NULL or an internal
entry.
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void *
xas_load(struct xa_state *xas)¶ Load an entry from the XArray (advanced).
Parameters
struct xa_state *xas- XArray operation state.
Description
Usually walks the xas to the appropriate state to load the entry
stored at xa_index. However, it will do nothing and return NULL if
xas is in an error state. xas_load() will never expand the tree.
If the xa_state is set up to operate on a multi-index entry, xas_load()
may return NULL or an internal entry, even if there are entries
present within the range specified by xas.
Context
Any context. The caller should hold the xa_lock or the RCU lock.
Return
Usually an entry in the XArray, but see description for exceptions.
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bool
xas_nomem(struct xa_state *xas, gfp_t gfp)¶ Allocate memory if needed.
Parameters
struct xa_state *xas- XArray operation state.
gfp_t gfp- Memory allocation flags.
Description
If we need to add new nodes to the XArray, we try to allocate memory
with GFP_NOWAIT while holding the lock, which will usually succeed.
If it fails, xas is flagged as needing memory to continue. The caller
should drop the lock and call xas_nomem(). If xas_nomem() succeeds,
the caller should retry the operation.
Forward progress is guaranteed as one node is allocated here and stored in the xa_state where it will be found by xas_alloc(). More nodes will likely be found in the slab allocator, but we do not tie them up here.
Return
true if memory was needed, and was successfully allocated.
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void
xas_free_nodes(struct xa_state *xas, struct xa_node *top)¶ Free this node and all nodes that it references
Parameters
struct xa_state *xas- Array operation state.
struct xa_node *top- Node to free
Description
This node has been removed from the tree. We must now free it and all of its subnodes. There may be RCU walkers with references into the tree, so we must replace all entries with retry markers.
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void
xas_create_range(struct xa_state *xas)¶ Ensure that stores to this range will succeed
Parameters
struct xa_state *xas- XArray operation state.
Description
Creates all of the slots in the range covered by xas. Sets xas to create single-index entries and positions it at the beginning of the range. This is for the benefit of users which have not yet been converted to use multi-index entries.
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void *
xas_store(struct xa_state *xas, void *entry)¶ Store this entry in the XArray.
Parameters
struct xa_state *xas- XArray operation state.
void *entry- New entry.
Description
If xas is operating on a multi-index entry, the entry returned by this
function is essentially meaningless (it may be an internal entry or it
may be NULL, even if there are non-NULL entries at some of the indices
covered by the range). This is not a problem for any current users,
and can be changed if needed.
Return
The old entry at this index.
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bool
xas_get_mark(const struct xa_state *xas, xa_mark_t mark)¶ Returns the state of this mark.
Parameters
const struct xa_state *xas- XArray operation state.
xa_mark_t mark- Mark number.
Return
true if the mark is set, false if the mark is clear or xas is in an error state.
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void
xas_set_mark(const struct xa_state *xas, xa_mark_t mark)¶ Sets the mark on this entry and its parents.
Parameters
const struct xa_state *xas- XArray operation state.
xa_mark_t mark- Mark number.
Description
Sets the specified mark on this entry, and walks up the tree setting it on all the ancestor entries. Does nothing if xas has not been walked to an entry, or is in an error state.
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void
xas_clear_mark(const struct xa_state *xas, xa_mark_t mark)¶ Clears the mark on this entry and its parents.
Parameters
const struct xa_state *xas- XArray operation state.
xa_mark_t mark- Mark number.
Description
Clears the specified mark on this entry, and walks back to the head attempting to clear it on all the ancestor entries. Does nothing if xas has not been walked to an entry, or is in an error state.
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void
xas_init_marks(const struct xa_state *xas)¶ Initialise all marks for the entry
Parameters
const struct xa_state *xas- Array operations state.
Description
Initialise all marks for the entry specified by xas. If we’re tracking free entries with a mark, we need to set it on all entries. All other marks are cleared.
This implementation is not as efficient as it could be; we may walk up the tree multiple times.
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void
xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order, gfp_t gfp)¶ Allocate memory for splitting an entry.
Parameters
struct xa_state *xas- XArray operation state.
void *entry- New entry which will be stored in the array.
unsigned int order- New entry order.
gfp_t gfp- Memory allocation flags.
Description
This function should be called before calling xas_split().
If necessary, it will allocate new nodes (and fill them with entry)
to prepare for the upcoming split of an entry of order size into
entries of the order stored in the xas.
Context
May sleep if gfp flags permit.
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void
xas_split(struct xa_state *xas, void *entry, unsigned int order)¶ Split a multi-index entry into smaller entries.
Parameters
struct xa_state *xas- XArray operation state.
void *entry- New entry to store in the array.
unsigned int order- New entry order.
Description
The value in the entry is copied to all the replacement entries.
Context
Any context. The caller should hold the xa_lock.
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void
xas_pause(struct xa_state *xas)¶ Pause a walk to drop a lock.
Parameters
struct xa_state *xas- XArray operation state.
Description
Some users need to pause a walk and drop the lock they’re holding in
order to yield to a higher priority thread or carry out an operation
on an entry. Those users should call this function before they drop
the lock. It resets the xas to be suitable for the next iteration
of the loop after the user has reacquired the lock. If most entries
found during a walk require you to call xas_pause(), the xa_for_each()
iterator may be more appropriate.
Note that xas_pause() only works for forward iteration. If a user needs
to pause a reverse iteration, we will need a xas_pause_rev().
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void *
xas_find(struct xa_state *xas, unsigned long max)¶ Find the next present entry in the XArray.
Parameters
struct xa_state *xas- XArray operation state.
unsigned long max- Highest index to return.
Description
If the xas has not yet been walked to an entry, return the entry which has an index >= xas.xa_index. If it has been walked, the entry currently being pointed at has been processed, and so we move to the next entry.
If no entry is found and the array is smaller than max, the iterator
is set to the smallest index not yet in the array. This allows xas
to be immediately passed to xas_store().
Return
The entry, if found, otherwise NULL.
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void *
xas_find_marked(struct xa_state *xas, unsigned long max, xa_mark_t mark)¶ Find the next marked entry in the XArray.
Parameters
struct xa_state *xas- XArray operation state.
unsigned long max- Highest index to return.
xa_mark_t mark- Mark number to search for.
Description
If the xas has not yet been walked to an entry, return the marked entry which has an index >= xas.xa_index. If it has been walked, the entry currently being pointed at has been processed, and so we return the first marked entry with an index > xas.xa_index.
If no marked entry is found and the array is smaller than max, xas is
set to the bounds state and xas->xa_index is set to the smallest index
not yet in the array. This allows xas to be immediately passed to
xas_store().
If no entry is found before max is reached, xas is set to the restart state.
Return
The entry, if found, otherwise NULL.
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void *
xas_find_conflict(struct xa_state *xas)¶ Find the next present entry in a range.
Parameters
struct xa_state *xas- XArray operation state.
Description
The xas describes both a range and a position within that range.
Context
Any context. Expects xa_lock to be held.
Return
The next entry in the range covered by xas or NULL.
Parameters
struct xarray *xa- XArray.
unsigned long index- index into array.
Context
Any context. Takes and releases the RCU lock.
Return
The entry at index in xa.
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void *
__xa_erase(struct xarray *xa, unsigned long index)¶ Erase this entry from the XArray while locked.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
Description
After this function returns, loading from index will return NULL.
If the index is part of a multi-index entry, all indices will be erased
and none of the entries will be part of a multi-index entry.
Context
Any context. Expects xa_lock to be held on entry.
Return
The entry which used to be at this index.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
Description
After this function returns, loading from index will return NULL.
If the index is part of a multi-index entry, all indices will be erased
and none of the entries will be part of a multi-index entry.
Context
Any context. Takes and releases the xa_lock.
Return
The entry which used to be at this index.
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void *
__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)¶ Store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
You must already be holding the xa_lock when calling this function. It will drop the lock if needed to allocate memory, and then reacquire it afterwards.
Context
Any context. Expects xa_lock to be held on entry. May release and reacquire xa_lock if gfp flags permit.
Return
The old entry at this index or xa_err() if an error happened.
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void *
xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)¶ Store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
After this function returns, loads from this index will return entry.
Storing into an existing multi-index entry updates the entry of every index.
The marks associated with index are unaffected unless entry is NULL.
Context
Any context. Takes and releases the xa_lock. May sleep if the gfp flags permit.
Return
The old entry at this index on success, xa_err(-EINVAL) if entry cannot be stored in an XArray, or xa_err(-ENOMEM) if memory allocation failed.
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void *
__xa_cmpxchg(struct xarray *xa, unsigned long index, void *old, void *entry, gfp_t gfp)¶ Store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *old- Old value to test against.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
You must already be holding the xa_lock when calling this function. It will drop the lock if needed to allocate memory, and then reacquire it afterwards.
Context
Any context. Expects xa_lock to be held on entry. May release and reacquire xa_lock if gfp flags permit.
Return
The old entry at this index or xa_err() if an error happened.
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int
__xa_insert(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)¶ Store this entry in the XArray if no entry is present.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index into array.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
Inserting a NULL entry will store a reserved entry (like xa_reserve())
if no entry is present. Inserting will fail if a reserved entry is
present, even though loading from this index will return NULL.
Context
Any context. Expects xa_lock to be held on entry. May release and reacquire xa_lock if gfp flags permit.
Return
0 if the store succeeded. -EBUSY if another entry was present. -ENOMEM if memory could not be allocated.
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void *
xa_store_range(struct xarray *xa, unsigned long first, unsigned long last, void *entry, gfp_t gfp)¶ Store this entry at a range of indices in the XArray.
Parameters
struct xarray *xa- XArray.
unsigned long first- First index to affect.
unsigned long last- Last index to affect.
void *entry- New entry.
gfp_t gfp- Memory allocation flags.
Description
After this function returns, loads from any index between first and last,
inclusive will return entry.
Storing into an existing multi-index entry updates the entry of every index.
The marks associated with index are unaffected unless entry is NULL.
Context
Process context. Takes and releases the xa_lock. May sleep if the gfp flags permit.
Return
NULL on success, xa_err(-EINVAL) if entry cannot be stored in
an XArray, or xa_err(-ENOMEM) if memory allocation failed.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of the entry.
Return
A number between 0 and 63 indicating the order of the entry.
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int
__xa_alloc(struct xarray *xa, u32 *id, void *entry, struct xa_limit limit, gfp_t gfp)¶ Find somewhere to store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
u32 *id- Pointer to ID.
void *entry- New entry.
struct xa_limit limit- Range for allocated ID.
gfp_t gfp- Memory allocation flags.
Description
Finds an empty entry in xa between limit.min and limit.max, stores the index into the id pointer, then stores the entry at that index. A concurrent lookup will not see an uninitialised id.
Context
Any context. Expects xa_lock to be held on entry. May release and reacquire xa_lock if gfp flags permit.
Return
0 on success, -ENOMEM if memory could not be allocated or -EBUSY if there are no free entries in limit.
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int
__xa_alloc_cyclic(struct xarray *xa, u32 *id, void *entry, struct xa_limit limit, u32 *next, gfp_t gfp)¶ Find somewhere to store this entry in the XArray.
Parameters
struct xarray *xa- XArray.
u32 *id- Pointer to ID.
void *entry- New entry.
struct xa_limit limit- Range of allocated ID.
u32 *next- Pointer to next ID to allocate.
gfp_t gfp- Memory allocation flags.
Description
Finds an empty entry in xa between limit.min and limit.max, stores the index into the id pointer, then stores the entry at that index. A concurrent lookup will not see an uninitialised id. The search for an empty entry will start at next and will wrap around if necessary.
Context
Any context. Expects xa_lock to be held on entry. May release and reacquire xa_lock if gfp flags permit.
Return
0 if the allocation succeeded without wrapping. 1 if the allocation succeeded after wrapping, -ENOMEM if memory could not be allocated or -EBUSY if there are no free entries in limit.
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void
__xa_set_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)¶ Set this mark on this entry while locked.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
xa_mark_t mark- Mark number.
Description
Attempting to set a mark on a NULL entry does not succeed.
Context
Any context. Expects xa_lock to be held on entry.
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void
__xa_clear_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)¶ Clear this mark on this entry while locked.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
xa_mark_t mark- Mark number.
Context
Any context. Expects xa_lock to be held on entry.
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bool
xa_get_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)¶ Inquire whether this mark is set on this entry.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
xa_mark_t mark- Mark number.
Description
This function uses the RCU read lock, so the result may be out of date by the time it returns. If you need the result to be stable, use a lock.
Context
Any context. Takes and releases the RCU lock.
Return
True if the entry at index has this mark set, false if it doesn’t.
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void
xa_set_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)¶ Set this mark on this entry.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
xa_mark_t mark- Mark number.
Description
Attempting to set a mark on a NULL entry does not succeed.
Context
Process context. Takes and releases the xa_lock.
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void
xa_clear_mark(struct xarray *xa, unsigned long index, xa_mark_t mark)¶ Clear this mark on this entry.
Parameters
struct xarray *xa- XArray.
unsigned long index- Index of entry.
xa_mark_t mark- Mark number.
Description
Clearing a mark always succeeds.
Context
Process context. Takes and releases the xa_lock.
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void *
xa_find(struct xarray *xa, unsigned long *indexp, unsigned long max, xa_mark_t filter)¶ Search the XArray for an entry.
Parameters
struct xarray *xa- XArray.
unsigned long *indexp- Pointer to an index.
unsigned long max- Maximum index to search to.
xa_mark_t filter- Selection criterion.
Description
Finds the entry in xa which matches the filter, and has the lowest
index that is at least indexp and no more than max.
If an entry is found, indexp is updated to be the index of the entry.
This function is protected by the RCU read lock, so it may not find
entries which are being simultaneously added. It will not return an
XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
Context
Any context. Takes and releases the RCU lock.
Return
The entry, if found, otherwise NULL.
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void *
xa_find_after(struct xarray *xa, unsigned long *indexp, unsigned long max, xa_mark_t filter)¶ Search the XArray for a present entry.
Parameters
struct xarray *xa- XArray.
unsigned long *indexp- Pointer to an index.
unsigned long max- Maximum index to search to.
xa_mark_t filter- Selection criterion.
Description
Finds the entry in xa which matches the filter and has the lowest
index that is above indexp and no more than max.
If an entry is found, indexp is updated to be the index of the entry.
This function is protected by the RCU read lock, so it may miss entries
which are being simultaneously added. It will not return an
XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
Context
Any context. Takes and releases the RCU lock.
Return
The pointer, if found, otherwise NULL.
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unsigned int
xa_extract(struct xarray *xa, void **dst, unsigned long start, unsigned long max, unsigned int n, xa_mark_t filter)¶ Copy selected entries from the XArray into a normal array.
Parameters
struct xarray *xa- The source XArray to copy from.
void **dst- The buffer to copy entries into.
unsigned long start- The first index in the XArray eligible to be selected.
unsigned long max- The last index in the XArray eligible to be selected.
unsigned int n- The maximum number of entries to copy.
xa_mark_t filter- Selection criterion.
Description
Copies up to n entries that match filter from the XArray. The copied entries will have indices between start and max, inclusive.
The filter may be an XArray mark value, in which case entries which are
marked with that mark will be copied. It may also be XA_PRESENT, in
which case all entries which are not NULL will be copied.
The entries returned may not represent a snapshot of the XArray at a
moment in time. For example, if another thread stores to index 5, then
index 10, calling xa_extract() may return the old contents of index 5
and the new contents of index 10. Indices not modified while this
function is running will not be skipped.
If you need stronger guarantees, holding the xa_lock across calls to this function will prevent concurrent modification.
Context
Any context. Takes and releases the RCU lock.
Return
The number of entries copied.
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void
xa_delete_node(struct xa_node *node, xa_update_node_t update)¶ Private interface for workingset code.
Parameters
struct xa_node *node- Node to be removed from the tree.
xa_update_node_t update- Function to call to update ancestor nodes.
Context
xa_lock must be held on entry and will not be released.
Parameters
struct xarray *xa- XArray.
Description
After calling this function, the XArray is empty and has freed all memory allocated for its internal data structures. You are responsible for freeing the objects referenced by the XArray.
Context
Any context. Takes and releases the xa_lock, interrupt-safe.