Linux Filesystems API summary¶

This section contains API-level documentation, mostly taken from the source code itself.

The Linux VFS¶

The Filesystem types¶

enum positive_aop_returns¶: aop return codes with specific semantics

Constants

AOP_WRITEPAGE_ACTIVATE: Informs the caller that page writeback has completed, that the page is still locked, and should be considered active. The VM uses this hint to return the page to the active list – it won’t be a candidate for writeback again in the near future. Other callers must be careful to unlock the page if they get this return. Returned by writepage();
AOP_TRUNCATED_PAGE: The AOP method that was handed a locked page has unlocked it and the page might have been truncated. The caller should back up to acquiring a new page and trying again. The aop will be taking reasonable precautions not to livelock. If the caller held a page reference, it should drop it before retrying. Returned by readpage().

Description

address_space_operation functions return these large constants to indicate special semantics to the caller. These are much larger than the bytes in a page to allow for functions that return the number of bytes operated on in a given page.

struct address_space¶: Contents of a cacheable, mappable object.

Definition

struct address_space {
  struct inode            *host;
  struct xarray           i_pages;
  gfp_t gfp_mask;
  atomic_t i_mmap_writable;
#ifdef CONFIG_READ_ONLY_THP_FOR_FS;
  atomic_t nr_thps;
#endif;
  struct rb_root_cached   i_mmap;
  struct rw_semaphore     i_mmap_rwsem;
  unsigned long           nrpages;
  unsigned long           nrexceptional;
  pgoff_t writeback_index;
  const struct address_space_operations *a_ops;
  unsigned long           flags;
  errseq_t wb_err;
  spinlock_t private_lock;
  struct list_head        private_list;
  void *private_data;
};

Members

host: Owner, either the inode or the block_device.
i_pages: Cached pages.
gfp_mask: Memory allocation flags to use for allocating pages.
i_mmap_writable: Number of VM_SHARED mappings.
nr_thps: Number of THPs in the pagecache (non-shmem only).
i_mmap: Tree of private and shared mappings.
i_mmap_rwsem: Protects i_mmap and i_mmap_writable.
nrpages: Number of page entries, protected by the i_pages lock.
nrexceptional: Shadow or DAX entries, protected by the i_pages lock.
writeback_index: Writeback starts here.
a_ops: Methods.
flags: Error bits and flags (AS_*).
wb_err: The most recent error which has occurred.
private_lock: For use by the owner of the address_space.
private_list: For use by the owner of the address_space.
private_data: For use by the owner of the address_space.

void sb_end_write(struct super_block *sb)¶: drop write access to a superblock

Parameters

struct super_block *sb: the super we wrote to

Description

Decrement number of writers to the filesystem. Wake up possible waiters wanting to freeze the filesystem.

void sb_end_pagefault(struct super_block *sb)¶: drop write access to a superblock from a page fault

Parameters

struct super_block *sb: the super we wrote to

Description

Decrement number of processes handling write page fault to the filesystem. Wake up possible waiters wanting to freeze the filesystem.

void sb_end_intwrite(struct super_block *sb)¶: drop write access to a superblock for internal fs purposes

Parameters

struct super_block *sb: the super we wrote to

Description

Decrement fs-internal number of writers to the filesystem. Wake up possible waiters wanting to freeze the filesystem.

void sb_start_write(struct super_block *sb)¶: get write access to a superblock

Parameters

struct super_block *sb: the super we write to

Description

When a process wants to write data or metadata to a file system (i.e. dirty a page or an inode), it should embed the operation in a sb_start_write() - sb_end_write() pair to get exclusion against file system freezing. This function increments number of writers preventing freezing. If the file system is already frozen, the function waits until the file system is thawed.

Since freeze protection behaves as a lock, users have to preserve ordering of freeze protection and other filesystem locks. Generally, freeze protection should be the outermost lock. In particular, we have:

sb_start_write: -> i_mutex (write path, truncate, directory ops, …) -> s_umount (freeze_super, thaw_super)

void sb_start_pagefault(struct super_block *sb)¶: get write access to a superblock from a page fault

Parameters

struct super_block *sb: the super we write to

Description

When a process starts handling write page fault, it should embed the operation into sb_start_pagefault() - sb_end_pagefault() pair to get exclusion against file system freezing. This is needed since the page fault is going to dirty a page. This function increments number of running page faults preventing freezing. If the file system is already frozen, the function waits until the file system is thawed.

Since page fault freeze protection behaves as a lock, users have to preserve ordering of freeze protection and other filesystem locks. It is advised to put sb_start_pagefault() close to mmap_lock in lock ordering. Page fault handling code implies lock dependency:

mmap_lock: -> sb_start_pagefault

void filemap_set_wb_err(struct address_space *mapping, int err)¶: set a writeback error on an address_space

Parameters

struct address_space *mapping: mapping in which to set writeback error
int err: error to be set in mapping

Description

When writeback fails in some way, we must record that error so that userspace can be informed when fsync and the like are called. We endeavor to report errors on any file that was open at the time of the error. Some internal callers also need to know when writeback errors have occurred.

When a writeback error occurs, most filesystems will want to call filemap_set_wb_err to record the error in the mapping so that it will be automatically reported whenever fsync is called on the file.

int filemap_check_wb_err(struct address_space *mapping, errseq_t since)¶: has an error occurred since the mark was sampled?

Parameters

struct address_space *mapping: mapping to check for writeback errors
errseq_t since: previously-sampled errseq_t

Description

Grab the errseq_t value from the mapping, and see if it has changed “since” the given value was sampled.

If it has then report the latest error set, otherwise return 0.

errseq_t filemap_sample_wb_err(struct address_space *mapping)¶: sample the current errseq_t to test for later errors

Parameters

struct address_space *mapping: mapping to be sampled

Description

Writeback errors are always reported relative to a particular sample point in the past. This function provides those sample points.

errseq_t file_sample_sb_err(struct file *file)¶: sample the current errseq_t to test for later errors

Parameters

struct file *file: file pointer to be sampled

Description

Grab the most current superblock-level errseq_t value for the given struct file.

The Directory Cache¶

struct dentry * d_find_any_alias(struct inode *inode)¶: find any alias for a given inode

Parameters

struct inode *inode: inode to find an alias for

Description

If any aliases exist for the given inode, take and return a reference for one of them. If no aliases exist, return NULL.

void shrink_dcache_sb(struct super_block *sb)¶: shrink dcache for a superblock

Parameters

struct super_block *sb: superblock

Description

Shrink the dcache for the specified super block. This is used to free the dcache before unmounting a file system.

int path_has_submounts(const struct path *parent)¶: check for mounts over a dentry in the current namespace.

Parameters

const struct path *parent: path to check.

Description

Return true if the parent or its subdirectories contain a mount point in the current namespace.

void shrink_dcache_parent(struct dentry *parent)¶: prune dcache

Parameters

struct dentry *parent: parent of entries to prune

Description

Prune the dcache to remove unused children of the parent dentry.

void d_invalidate(struct dentry *dentry)¶: detach submounts, prune dcache, and drop

Parameters

struct dentry *dentry: dentry to invalidate (aka detach, prune and drop)

struct dentry * d_alloc(struct dentry * parent, const struct qstr *name)¶: allocate a dcache entry

Parameters

struct dentry * parent: parent of entry to allocate
const struct qstr *name: qstr of the name

Description

Allocates a dentry. It returns NULL if there is insufficient memory available. On a success the dentry is returned. The name passed in is copied and the copy passed in may be reused after this call.

void d_instantiate(struct dentry *entry, struct inode * inode)¶: fill in inode information for a dentry

Parameters

struct dentry *entry: dentry to complete
struct inode * inode: inode to attach to this dentry

Description

Fill in inode information in the entry.

This turns negative dentries into productive full members of society.

NOTE! This assumes that the inode count has been incremented (or otherwise set) by the caller to indicate that it is now in use by the dcache.

struct dentry * d_obtain_alias(struct inode *inode)¶: find or allocate a DISCONNECTED dentry for a given inode

Parameters

struct inode *inode: inode to allocate the dentry for

Description

Obtain a dentry for an inode resulting from NFS filehandle conversion or similar open by handle operations. The returned dentry may be anonymous, or may have a full name (if the inode was already in the cache).

When called on a directory inode, we must ensure that the inode only ever has one dentry. If a dentry is found, that is returned instead of allocating a new one.

On successful return, the reference to the inode has been transferred to the dentry. In case of an error the reference on the inode is released. To make it easier to use in export operations a NULL or IS_ERR inode may be passed in and the error will be propagated to the return value, with a NULL inode replaced by ERR_PTR(-ESTALE).

struct dentry * d_obtain_root(struct inode *inode)¶: find or allocate a dentry for a given inode

Parameters

struct inode *inode: inode to allocate the dentry for

Description

Obtain an IS_ROOT dentry for the root of a filesystem.

We must ensure that directory inodes only ever have one dentry. If a dentry is found, that is returned instead of allocating a new one.

On successful return, the reference to the inode has been transferred to the dentry. In case of an error the reference on the inode is released. A NULL or IS_ERR inode may be passed in and will be the error will be propagate to the return value, with a NULL inode replaced by ERR_PTR(-ESTALE).

struct dentry * d_add_ci(struct dentry *dentry, struct inode *inode, struct qstr *name)¶: lookup or allocate new dentry with case-exact name

Parameters

struct dentry *dentry: the negative dentry that was passed to the parent’s lookup func
struct inode *inode: the inode case-insensitive lookup has found
struct qstr *name: the case-exact name to be associated with the returned dentry

Description

This is to avoid filling the dcache with case-insensitive names to the same inode, only the actual correct case is stored in the dcache for case-insensitive filesystems.

For a case-insensitive lookup match and if the the case-exact dentry already exists in in the dcache, use it and return it.

If no entry exists with the exact case name, allocate new dentry with the exact case, and return the spliced entry.

struct dentry * d_lookup(const struct dentry *parent, const struct qstr *name)¶: search for a dentry

Parameters

const struct dentry *parent: parent dentry
const struct qstr *name: qstr of name we wish to find

Return

dentry, or NULL

Description

d_lookup searches the children of the parent dentry for the name in question. If the dentry is found its reference count is incremented and the dentry is returned. The caller must use dput to free the entry when it has finished using it. NULL is returned if the dentry does not exist.

struct dentry * d_hash_and_lookup(struct dentry *dir, struct qstr *name)¶: hash the qstr then search for a dentry

Parameters

struct dentry *dir: Directory to search in
struct qstr *name: qstr of name we wish to find

Description

On lookup failure NULL is returned; on bad name - ERR_PTR(-error)

void d_delete(struct dentry * dentry)¶: delete a dentry

Parameters

struct dentry * dentry: The dentry to delete

Description

Turn the dentry into a negative dentry if possible, otherwise remove it from the hash queues so it can be deleted later

void d_rehash(struct dentry * entry)¶: add an entry back to the hash

Parameters

struct dentry * entry: dentry to add to the hash

Description

Adds a dentry to the hash according to its name.

void d_add(struct dentry *entry, struct inode *inode)¶: add dentry to hash queues

Parameters

struct dentry *entry: dentry to add
struct inode *inode: The inode to attach to this dentry

Description

This adds the entry to the hash queues and initializes inode. The entry was actually filled in earlier during d_alloc().

struct dentry * d_exact_alias(struct dentry *entry, struct inode *inode)¶: find and hash an exact unhashed alias

Parameters

struct dentry *entry: dentry to add
struct inode *inode: The inode to go with this dentry

Description

If an unhashed dentry with the same name/parent and desired inode already exists, hash and return it. Otherwise, return NULL.

Parent directory should be locked.

struct dentry * d_splice_alias(struct inode *inode, struct dentry *dentry)¶: splice a disconnected dentry into the tree if one exists

Parameters

struct inode *inode: the inode which may have a disconnected dentry
struct dentry *dentry: a negative dentry which we want to point to the inode.

Description

If inode is a directory and has an IS_ROOT alias, then d_move that in place of the given dentry and return it, else simply d_add the inode to the dentry and return NULL.

If a non-IS_ROOT directory is found, the filesystem is corrupt, and we should error out: directories can’t have multiple aliases.

This is needed in the lookup routine of any filesystem that is exportable (via knfsd) so that we can build dcache paths to directories effectively.

If a dentry was found and moved, then it is returned. Otherwise NULL is returned. This matches the expected return value of ->lookup.

Cluster filesystems may call this function with a negative, hashed dentry. In that case, we know that the inode will be a regular file, and also this will only occur during atomic_open. So we need to check for the dentry being already hashed only in the final case.

bool is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)¶: is new dentry a subdirectory of old_dentry

Parameters

struct dentry *new_dentry: new dentry
struct dentry *old_dentry: old dentry

Description

Returns true if new_dentry is a subdirectory of the parent (at any depth). Returns false otherwise. Caller must ensure that “new_dentry” is pinned before calling is_subdir()

struct dentry * dget_dlock(struct dentry *dentry)¶: get a reference to a dentry

Parameters

struct dentry *dentry

dentry to get a reference to

Given a dentry or NULL pointer increment the reference count if appropriate and return the dentry. A dentry will not be destroyed when it has references.

int d_unhashed(const struct dentry *dentry)¶: is dentry hashed

Parameters

const struct dentry *dentry

entry to check

Returns true if the dentry passed is not currently hashed.

bool d_really_is_negative(const struct dentry *dentry)¶: Determine if a dentry is really negative (ignoring fallthroughs)

Parameters

const struct dentry *dentry: The dentry in question

Description

Returns true if the dentry represents either an absent name or a name that doesn’t map to an inode (ie. ->d_inode is NULL). The dentry could represent a true miss, a whiteout that isn’t represented by a 0,0 chardev or a fallthrough marker in an opaque directory.

Note! (1) This should be used only by a filesystem to examine its own dentries. It should not be used to look at some other filesystem’s dentries. (2) It should also be used in combination with d_inode() to get the inode. (3) The dentry may have something attached to ->d_lower and the type field of the flags may be set to something other than miss or whiteout.

bool d_really_is_positive(const struct dentry *dentry)¶: Determine if a dentry is really positive (ignoring fallthroughs)

Parameters

const struct dentry *dentry: The dentry in question

Description

Returns true if the dentry represents a name that maps to an inode (ie. ->d_inode is not NULL). The dentry might still represent a whiteout if that is represented on medium as a 0,0 chardev.

Note! (1) This should be used only by a filesystem to examine its own dentries. It should not be used to look at some other filesystem’s dentries. (2) It should also be used in combination with d_inode() to get the inode.

struct inode * d_inode(const struct dentry *dentry)¶: Get the actual inode of this dentry

Parameters

const struct dentry *dentry: The dentry to query

Description

This is the helper normal filesystems should use to get at their own inodes in their own dentries and ignore the layering superimposed upon them.

struct inode * d_inode_rcu(const struct dentry *dentry)¶: Get the actual inode of this dentry with READ_ONCE()

Parameters

const struct dentry *dentry: The dentry to query

Description

This is the helper normal filesystems should use to get at their own inodes in their own dentries and ignore the layering superimposed upon them.

struct inode * d_backing_inode(const struct dentry *upper)¶: Get upper or lower inode we should be using

Parameters

const struct dentry *upper: The upper layer

Description

This is the helper that should be used to get at the inode that will be used if this dentry were to be opened as a file. The inode may be on the upper dentry or it may be on a lower dentry pinned by the upper.

Normal filesystems should not use this to access their own inodes.

struct dentry * d_backing_dentry(struct dentry *upper)¶: Get upper or lower dentry we should be using

Parameters

struct dentry *upper: The upper layer

Description

This is the helper that should be used to get the dentry of the inode that will be used if this dentry were opened as a file. It may be the upper dentry or it may be a lower dentry pinned by the upper.

Normal filesystems should not use this to access their own dentries.

struct dentry * d_real(struct dentry *dentry, const struct inode *inode)¶: Return the real dentry

Parameters

struct dentry *dentry: the dentry to query
const struct inode *inode: inode to select the dentry from multiple layers (can be NULL)

Description

If dentry is on a union/overlay, then return the underlying, real dentry. Otherwise return the dentry itself.

struct inode * d_real_inode(const struct dentry *dentry)¶: Return the real inode

Parameters

const struct dentry *dentry: The dentry to query

Description

If dentry is on a union/overlay, then return the underlying, real inode. Otherwise return d_inode().

Inode Handling¶

int inode_init_always(struct super_block *sb, struct inode *inode)¶: perform inode structure initialisation

Parameters

struct super_block *sb: superblock inode belongs to
struct inode *inode: inode to initialise

Description

These are initializations that need to be done on every inode allocation as the fields are not initialised by slab allocation.

void drop_nlink(struct inode *inode)¶: directly drop an inode’s link count

Parameters

struct inode *inode: inode

Description

This is a low-level filesystem helper to replace any direct filesystem manipulation of i_nlink. In cases where we are attempting to track writes to the filesystem, a decrement to zero means an imminent write when the file is truncated and actually unlinked on the filesystem.

void clear_nlink(struct inode *inode)¶: directly zero an inode’s link count

Parameters

struct inode *inode: inode

Description

This is a low-level filesystem helper to replace any direct filesystem manipulation of i_nlink. See drop_nlink() for why we care about i_nlink hitting zero.

void set_nlink(struct inode *inode, unsigned int nlink)¶: directly set an inode’s link count

Parameters

struct inode *inode: inode
unsigned int nlink: new nlink (should be non-zero)

Description

This is a low-level filesystem helper to replace any direct filesystem manipulation of i_nlink.

void inc_nlink(struct inode *inode)¶: directly increment an inode’s link count

Parameters

struct inode *inode: inode

Description

This is a low-level filesystem helper to replace any direct filesystem manipulation of i_nlink. Currently, it is only here for parity with dec_nlink().

void inode_sb_list_add(struct inode *inode)¶: add inode to the superblock list of inodes

Parameters

struct inode *inode: inode to add

void __insert_inode_hash(struct inode *inode, unsigned long hashval)¶: hash an inode

Parameters

struct inode *inode: unhashed inode
unsigned long hashval: unsigned long value used to locate this object in the inode_hashtable.

Add an inode to the inode hash for this superblock.

void __remove_inode_hash(struct inode *inode)¶: remove an inode from the hash

Parameters

struct inode *inode

inode to unhash

Remove an inode from the superblock.

void evict_inodes(struct super_block *sb)¶: evict all evictable inodes for a superblock

Parameters

struct super_block *sb: superblock to operate on

Description

Make sure that no inodes with zero refcount are retained. This is called by superblock shutdown after having SB_ACTIVE flag removed, so any inode reaching zero refcount during or after that call will be immediately evicted.

struct inode * new_inode(struct super_block *sb)¶: obtain an inode

Parameters

struct super_block *sb

superblock

Allocates a new inode for given superblock. The default gfp_mask for allocations related to inode->i_mapping is GFP_HIGHUSER_MOVABLE. If HIGHMEM pages are unsuitable or it is known that pages allocated for the page cache are not reclaimable or migratable, mapping_set_gfp_mask() must be called with suitable flags on the newly created inode’s mapping

void unlock_new_inode(struct inode *inode)¶: clear the I_NEW state and wake up any waiters

Parameters

struct inode *inode: new inode to unlock

Description

Called when the inode is fully initialised to clear the new state of the inode and wake up anyone waiting for the inode to finish initialisation.

void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)¶: take two i_mutexes on non-directory objects

Parameters

struct inode *inode1: first inode to lock
struct inode *inode2: second inode to lock

Description

Lock any non-NULL argument that is not a directory. Zero, one or two objects may be locked by this function.

void unlock_two_nondirectories(struct inode *inode1, struct inode *inode2)¶: release locks from lock_two_nondirectories()

Parameters

struct inode *inode1: first inode to unlock
struct inode *inode2: second inode to unlock

struct inode * inode_insert5(struct inode *inode, unsigned long hashval, int (*test)(struct inode *, void *), int (*set)(struct inode *, void *), void *data)¶: obtain an inode from a mounted file system

Parameters

struct inode *inode: pre-allocated inode to use for insert to cache
unsigned long hashval: hash value (usually inode number) to get
int (*test)(struct inode *, void *): callback used for comparisons between inodes
int (*set)(struct inode *, void *): callback used to initialize a new struct inode
void *data: opaque data pointer to pass to test and set

Description

Search for the inode specified by hashval and data in the inode cache, and if present it is return it with an increased reference count. This is a variant of iget5_locked() for callers that don’t want to fail on memory allocation of inode.

If the inode is not in cache, insert the pre-allocated inode to cache and return it locked, hashed, and with the I_NEW flag set. The file system gets to fill it in before unlocking it via unlock_new_inode().

Note both test and set are called with the inode_hash_lock held, so can’t sleep.

struct inode * iget5_locked(struct super_block *sb, unsigned long hashval, int (*test)(struct inode *, void *), int (*set)(struct inode *, void *), void *data)¶: obtain an inode from a mounted file system

Parameters

struct super_block *sb: super block of file system
unsigned long hashval: hash value (usually inode number) to get
int (*test)(struct inode *, void *): callback used for comparisons between inodes
int (*set)(struct inode *, void *): callback used to initialize a new struct inode
void *data: opaque data pointer to pass to test and set

Description

Search for the inode specified by hashval and data in the inode cache, and if present it is return it with an increased reference count. This is a generalized version of iget_locked() for file systems where the inode number is not sufficient for unique identification of an inode.

If the inode is not in cache, allocate a new inode and return it locked, hashed, and with the I_NEW flag set. The file system gets to fill it in before unlocking it via unlock_new_inode().

Note both test and set are called with the inode_hash_lock held, so can’t sleep.

struct inode * iget_locked(struct super_block *sb, unsigned long ino)¶: obtain an inode from a mounted file system

Parameters

struct super_block *sb: super block of file system
unsigned long ino: inode number to get

Description

Search for the inode specified by ino in the inode cache and if present return it with an increased reference count. This is for file systems where the inode number is sufficient for unique identification of an inode.

If the inode is not in cache, allocate a new inode and return it locked, hashed, and with the I_NEW flag set. The file system gets to fill it in before unlocking it via unlock_new_inode().

ino_t iunique(struct super_block *sb, ino_t max_reserved)¶: get a unique inode number

Parameters

struct super_block *sb

superblock

ino_t max_reserved

highest reserved inode number

Obtain an inode number that is unique on the system for a given superblock. This is used by file systems that have no natural permanent inode numbering system. An inode number is returned that is higher than the reserved limit but unique.

BUGS: With a large number of inodes live on the file system this function currently becomes quite slow.

struct inode * ilookup5_nowait(struct super_block *sb, unsigned long hashval, int (*test)(struct inode *, void *), void *data)¶: search for an inode in the inode cache

Parameters

struct super_block *sb: super block of file system to search
unsigned long hashval: hash value (usually inode number) to search for
int (*test)(struct inode *, void *): callback used for comparisons between inodes
void *data: opaque data pointer to pass to test

Description

Search for the inode specified by hashval and data in the inode cache. If the inode is in the cache, the inode is returned with an incremented reference count.

Note2: test is called with the inode_hash_lock held, so can’t sleep.

Note

I_NEW is not waited upon so you have to be very careful what you do with the returned inode. You probably should be using ilookup5() instead.

struct inode * ilookup5(struct super_block *sb, unsigned long hashval, int (*test)(struct inode *, void *), void *data)¶: search for an inode in the inode cache

Parameters

struct super_block *sb: super block of file system to search
unsigned long hashval: hash value (usually inode number) to search for
int (*test)(struct inode *, void *): callback used for comparisons between inodes
void *data: opaque data pointer to pass to test

Description

Search for the inode specified by hashval and data in the inode cache, and if the inode is in the cache, return the inode with an incremented reference count. Waits on I_NEW before returning the inode. returned with an incremented reference count.

This is a generalized version of ilookup() for file systems where the inode number is not sufficient for unique identification of an inode.

Note

test is called with the inode_hash_lock held, so can’t sleep.

struct inode * ilookup(struct super_block *sb, unsigned long ino)¶: search for an inode in the inode cache

Parameters

struct super_block *sb: super block of file system to search
unsigned long ino: inode number to search for

Description

Search for the inode ino in the inode cache, and if the inode is in the cache, the inode is returned with an incremented reference count.

struct inode * find_inode_nowait(struct super_block *sb, unsigned long hashval, int (*match)(struct inode *, unsigned long, void *), void *data)¶: find an inode in the inode cache

Parameters

struct super_block *sb: super block of file system to search
unsigned long hashval: hash value (usually inode number) to search for
int (*match)(struct inode *, unsigned long, void *): callback used for comparisons between inodes
void *data: opaque data pointer to pass to match

Description

Search for the inode specified by hashval and data in the inode cache, where the helper function match will return 0 if the inode does not match, 1 if the inode does match, and -1 if the search should be stopped. The match function must be responsible for taking the i_lock spin_lock and checking i_state for an inode being freed or being initialized, and incrementing the reference count before returning 1. It also must not sleep, since it is called with the inode_hash_lock spinlock held.

This is a even more generalized version of ilookup5() when the function must never block — find_inode() can block in __wait_on_freeing_inode() — or when the caller can not increment the reference count because the resulting iput() might cause an inode eviction. The tradeoff is that the match funtion must be very carefully implemented.

struct inode * find_inode_rcu(struct super_block *sb, unsigned long hashval, int (*test)(struct inode *, void *), void *data)¶: find an inode in the inode cache

Parameters

struct super_block *sb: Super block of file system to search
unsigned long hashval: Key to hash
int (*test)(struct inode *, void *): Function to test match on an inode
void *data: Data for test function

Description

Search for the inode specified by hashval and data in the inode cache, where the helper function test will return 0 if the inode does not match and 1 if it does. The test function must be responsible for taking the i_lock spin_lock and checking i_state for an inode being freed or being initialized.

If successful, this will return the inode for which the test function returned 1 and NULL otherwise.

The test function is not permitted to take a ref on any inode presented. It is also not permitted to sleep.

The caller must hold the RCU read lock.

struct inode * find_inode_by_ino_rcu(struct super_block *sb, unsigned long ino)¶: Find an inode in the inode cache

Parameters

struct super_block *sb: Super block of file system to search
unsigned long ino: The inode number to match

Description

Search for the inode specified by hashval and data in the inode cache, where the helper function test will return 0 if the inode does not match and 1 if it does. The test function must be responsible for taking the i_lock spin_lock and checking i_state for an inode being freed or being initialized.

If successful, this will return the inode for which the test function returned 1 and NULL otherwise.

The test function is not permitted to take a ref on any inode presented. It is also not permitted to sleep.

The caller must hold the RCU read lock.

void iput(struct inode *inode)¶: put an inode

Parameters

struct inode *inode

inode to put

Puts an inode, dropping its usage count. If the inode use count hits zero, the inode is then freed and may also be destroyed.

Consequently, iput() can sleep.

int bmap(struct inode *inode, sector_t *block)¶: find a block number in a file

Parameters

struct inode *inode

inode owning the block number being requested

sector_t *block

pointer containing the block to find

Replaces the value in *block with the block number on the device holding corresponding to the requested block number in the file. That is, asked for block 4 of inode 1 the function will replace the 4 in *block, with disk block relative to the disk start that holds that block of the file.

Returns -EINVAL in case of error, 0 otherwise. If mapping falls into a hole, returns 0 and *block is also set to 0.

int file_update_time(struct file *file)¶: update mtime and ctime time

Parameters

struct file *file

file accessed

Update the mtime and ctime members of an inode and mark the inode for writeback. Note that this function is meant exclusively for usage in the file write path of filesystems, and filesystems may choose to explicitly ignore update via this function with the S_NOCMTIME inode flag, e.g. for network filesystem where these timestamps are handled by the server. This can return an error for file systems who need to allocate space in order to update an inode.

void inode_init_owner(struct inode *inode, const struct inode *dir, umode_t mode)¶: Init uid,gid,mode for new inode according to posix standards

Parameters

struct inode *inode: New inode
const struct inode *dir: Directory inode
umode_t mode: mode of the new inode

bool inode_owner_or_capable(const struct inode *inode)¶: check current task permissions to inode

Parameters

const struct inode *inode: inode being checked

Description

Return true if current either has CAP_FOWNER in a namespace with the inode owner uid mapped, or owns the file.

void inode_dio_wait(struct inode *inode)¶: wait for outstanding DIO requests to finish

Parameters

struct inode *inode: inode to wait for

Description

Waits for all pending direct I/O requests to finish so that we can proceed with a truncate or equivalent operation.

Must be called under a lock that serializes taking new references to i_dio_count, usually by inode->i_mutex.

struct timespec64 timestamp_truncate(struct timespec64 t, struct inode *inode)¶: Truncate timespec to a granularity

Parameters

struct timespec64 t: Timespec
struct inode *inode: inode being updated

Description

Truncate a timespec to the granularity supported by the fs containing the inode. Always rounds down. gran must not be 0 nor greater than a second (NSEC_PER_SEC, or 10^9 ns).

struct timespec64 current_time(struct inode *inode)¶: Return FS time

Parameters

struct inode *inode: inode.

Description

Return the current time truncated to the time granularity supported by the fs.

Note that inode and inode->sb cannot be NULL. Otherwise, the function warns and returns time without truncation.

void make_bad_inode(struct inode *inode)¶: mark an inode bad due to an I/O error

Parameters

struct inode *inode

Inode to mark bad

When an inode cannot be read due to a media or remote network failure this function makes the inode “bad” and causes I/O operations on it to fail from this point on.

bool is_bad_inode(struct inode *inode)¶: is an inode errored

Parameters

struct inode *inode

inode to test

Returns true if the inode in question has been marked as bad.

void iget_failed(struct inode *inode)¶: Mark an under-construction inode as dead and release it

Parameters

struct inode *inode: The inode to discard

Description

Mark an under-construction inode as dead and release it.

Registration and Superblocks¶

void deactivate_locked_super(struct super_block *s)¶: drop an active reference to superblock

Parameters

struct super_block *s

superblock to deactivate

Drops an active reference to superblock, converting it into a temporary one if there is no other active references left. In that case we tell fs driver to shut it down and drop the temporary reference we had just acquired.

Caller holds exclusive lock on superblock; that lock is released.

void deactivate_super(struct super_block *s)¶: drop an active reference to superblock

Parameters

struct super_block *s

superblock to deactivate

Variant of deactivate_locked_super(), except that superblock is not locked by caller. If we are going to drop the final active reference, lock will be acquired prior to that.

void generic_shutdown_super(struct super_block *sb)¶: common helper for ->kill_sb()

Parameters

struct super_block *sb

superblock to kill

generic_shutdown_super() does all fs-independent work on superblock shutdown. Typical ->kill_sb() should pick all fs-specific objects that need destruction out of superblock, call generic_shutdown_super() and release aforementioned objects. Note: dentries and inodes _are_ taken care of and do not need specific handling.

Upon calling this function, the filesystem may no longer alter or rearrange the set of dentries belonging to this super_block, nor may it change the attachments of dentries to inodes.

struct super_block * sget_fc(struct fs_context *fc, int (*test)(struct super_block *, struct fs_context *), int (*set)(struct super_block *, struct fs_context *))¶: Find or create a superblock

Parameters

struct fs_context *fc: Filesystem context.
int (*test)(struct super_block *, struct fs_context *): Comparison callback
int (*set)(struct super_block *, struct fs_context *): Setup callback

Description

Find or create a superblock using the parameters stored in the filesystem context and the two callback functions.

If an extant superblock is matched, then that will be returned with an elevated reference count that the caller must transfer or discard.

If no match is made, a new superblock will be allocated and basic initialisation will be performed (s_type, s_fs_info and s_id will be set and the set() callback will be invoked), the superblock will be published and it will be returned in a partially constructed state with SB_BORN and SB_ACTIVE as yet unset.

struct super_block * sget(struct file_system_type *type, int (*test)(struct super_block *,void *), int (*set)(struct super_block *,void *), int flags, void *data)¶: find or create a superblock

Parameters

struct file_system_type *type: filesystem type superblock should belong to
int (*test)(struct super_block *,void *): comparison callback
int (*set)(struct super_block *,void *): setup callback
int flags: mount flags
void *data: argument to each of them

void iterate_supers_type(struct file_system_type *type, void (*f)(struct super_block *, void *), void *arg)¶: call function for superblocks of given type

Parameters

struct file_system_type *type

fs type

void (*f)(struct super_block *, void *)

function to call

void *arg

argument to pass to it

Scans the superblock list and calls given function, passing it locked superblock and given argument.

int get_anon_bdev(dev_t *p)¶: Allocate a block device for filesystems which don’t have one.

Parameters

dev_t *p: Pointer to a dev_t.

Description

Filesystems which don’t use real block devices can call this function to allocate a virtual block device.

Context

Any context. Frequently called while holding sb_lock.

Return

0 on success, -EMFILE if there are no anonymous bdevs left or -ENOMEM if memory allocation failed.

int vfs_get_super(struct fs_context *fc, enum vfs_get_super_keying keying, int (*fill_super)(struct super_block *sb, struct fs_context *fc))¶: Get a superblock with a search key set in s_fs_info.

Parameters

struct fs_context *fc: The filesystem context holding the parameters
enum vfs_get_super_keying keying: How to distinguish superblocks
int (*fill_super)(struct super_block *sb, struct fs_context *fc): Helper to initialise a new superblock

Description

Search for a superblock and create a new one if not found. The search criterion is controlled by keying. If the search fails, a new superblock is created and fill_super() is called to initialise it.

keying can take one of a number of values:

vfs_get_single_super - Only one superblock of this type may exist on the system. This is typically used for special system filesystems.
vfs_get_keyed_super - Multiple superblocks may exist, but they must have distinct keys (where the key is in s_fs_info). Searching for the same key again will turn up the superblock for that key.
vfs_get_independent_super - Multiple superblocks may exist and are unkeyed. Each call will get a new superblock.

A permissions check is made by sget_fc() unless we’re getting a superblock for a kernel-internal mount or a submount.

int get_tree_bdev(struct fs_context *fc, int (*fill_super)(struct super_block *, struct fs_context *))¶: Get a superblock based on a single block device

Parameters

struct fs_context *fc: The filesystem context holding the parameters
int (*fill_super)(struct super_block *, struct fs_context *): Helper to initialise a new superblock

int vfs_get_tree(struct fs_context *fc)¶: Get the mountable root

Parameters

struct fs_context *fc: The superblock configuration context.

Description

The filesystem is invoked to get or create a superblock which can then later be used for mounting. The filesystem places a pointer to the root to be used for mounting in fc->root.

int freeze_super(struct super_block *sb)¶: lock the filesystem and force it into a consistent state

Parameters

struct super_block *sb: the super to lock

Description

Syncs the super to make sure the filesystem is consistent and calls the fs’s freeze_fs. Subsequent calls to this without first thawing the fs will return -EBUSY.

During this function, sb->s_writers.frozen goes through these values:

SB_UNFROZEN: File system is normal, all writes progress as usual.

SB_FREEZE_WRITE: The file system is in the process of being frozen. New writes should be blocked, though page faults are still allowed. We wait for all writes to complete and then proceed to the next stage.

SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked but internal fs threads can still modify the filesystem (although they should not dirty new pages or inodes), writeback can run etc. After waiting for all running page faults we sync the filesystem which will clean all dirty pages and inodes (no new dirty pages or inodes can be created when sync is running).

SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs modification are blocked (e.g. XFS preallocation truncation on inode reclaim). This is usually implemented by blocking new transactions for filesystems that have them and need this additional guard. After all internal writers are finished we call ->freeze_fs() to finish filesystem freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is mostly auxiliary for filesystems to verify they do not modify frozen fs.

sb->s_writers.frozen is protected by sb->s_umount.

File Locks¶

int locks_delete_block(struct file_lock *waiter)¶: stop waiting for a file lock

Parameters

struct file_lock *waiter

the lock which was waiting

lockd/nfsd need to disconnect the lock while working on it.

int posix_lock_file(struct file *filp, struct file_lock *fl, struct file_lock *conflock)¶: Apply a POSIX-style lock to a file

Parameters

struct file *filp: The file to apply the lock to
struct file_lock *fl: The lock to be applied
struct file_lock *conflock: Place to return a copy of the conflicting lock, if found.

Description

Add a POSIX style lock to a file. We merge adjacent & overlapping locks whenever possible. POSIX locks are sorted by owner task, then by starting address

Note that if called with an FL_EXISTS argument, the caller may determine whether or not a lock was successfully freed by testing the return value for -ENOENT.

int locks_mandatory_area(struct inode *inode, struct file *filp, loff_t start, loff_t end, unsigned char type)¶: Check for a conflicting lock

Parameters

struct inode *inode: the file to check
struct file *filp: how the file was opened (if it was)
loff_t start: first byte in the file to check
loff_t end: lastbyte in the file to check
unsigned char type: F_WRLCK for a write lock, else F_RDLCK

Description

Searches the inode’s list of locks to find any POSIX locks which conflict.

int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)¶: revoke all outstanding leases on file

Parameters

struct inode *inode: the inode of the file to return
unsigned int mode: O_RDONLY: break only write leases; O_WRONLY or O_RDWR: break all leases
unsigned int type: FL_LEASE: break leases and delegations; FL_DELEG: break only delegations

break_lease (inlined for speed) has checked there already is at least some kind of lock (maybe a lease) on this file. Leases are broken on a call to open() or truncate(). This function can sleep unless you specified O_NONBLOCK to your open().

void lease_get_mtime(struct inode *inode, struct timespec64 *time)¶: update modified time of an inode with exclusive lease

Parameters

struct inode *inode: the inode
struct timespec64 *time: pointer to a timespec which contains the last modified time

Description

This is to force NFS clients to flush their caches for files with exclusive leases. The justification is that if someone has an exclusive lease, then they could be modifying it.

int generic_setlease(struct file *filp, long arg, struct file_lock **flp, void **priv)¶: sets a lease on an open file

Parameters

struct file *filp: file pointer
long arg: type of lease to obtain
struct file_lock **flp: input - file_lock to use, output - file_lock inserted
void **priv: private data for lm_setup (may be NULL if lm_setup doesn’t require it)

The (input) flp->fl_lmops->lm_break function is required by break_lease().

int vfs_setlease(struct file *filp, long arg, struct file_lock **lease, void **priv)¶: sets a lease on an open file

Parameters

struct file *filp: file pointer
long arg: type of lease to obtain
struct file_lock **lease: file_lock to use when adding a lease
void **priv: private info for lm_setup when adding a lease (may be NULL if lm_setup doesn’t require it)

Description

Call this to establish a lease on the file. The “lease” argument is not used for F_UNLCK requests and may be NULL. For commands that set or alter an existing lease, the (*lease)->fl_lmops->lm_break operation must be set; if not, this function will return -ENOLCK (and generate a scary-looking stack trace).

The “priv” pointer is passed directly to the lm_setup function as-is. It may be NULL if the lm_setup operation doesn’t require it.

int locks_lock_inode_wait(struct inode *inode, struct file_lock *fl)¶: Apply a lock to an inode

Parameters

struct inode *inode: inode of the file to apply to
struct file_lock *fl: The lock to be applied

Description

Apply a POSIX or FLOCK style lock request to an inode.

int vfs_test_lock(struct file *filp, struct file_lock *fl)¶: test file byte range lock

Parameters

struct file *filp: The file to test lock for
struct file_lock *fl: The lock to test; also used to hold result

Description

Returns -ERRNO on failure. Indicates presence of conflicting lock by setting conf->fl_type to something other than F_UNLCK.

int vfs_lock_file(struct file *filp, unsigned int cmd, struct file_lock *fl, struct file_lock *conf)¶: file byte range lock

Parameters

struct file *filp: The file to apply the lock to
unsigned int cmd: type of locking operation (F_SETLK, F_GETLK, etc.)
struct file_lock *fl: The lock to be applied
struct file_lock *conf: Place to return a copy of the conflicting lock, if found.

Description

A caller that doesn’t care about the conflicting lock may pass NULL as the final argument.

If the filesystem defines a private ->lock() method, then conf will be left unchanged; so a caller that cares should initialize it to some acceptable default.

To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX locks, the ->lock() interface may return asynchronously, before the lock has been granted or denied by the underlying filesystem, if (and only if) lm_grant is set. Callers expecting ->lock() to return asynchronously will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if) the request is for a blocking lock. When ->lock() does return asynchronously, it must return FILE_LOCK_DEFERRED, and call ->lm_grant() when the lock request completes. If the request is for non-blocking lock the file system should return FILE_LOCK_DEFERRED then try to get the lock and call the callback routine with the result. If the request timed out the callback routine will return a nonzero return code and the file system should release the lock. The file system is also responsible to keep a corresponding posix lock when it grants a lock so the VFS can find out which locks are locally held and do the correct lock cleanup when required. The underlying filesystem must not drop the kernel lock or call ->lm_grant() before returning to the caller with a FILE_LOCK_DEFERRED return code.

int vfs_cancel_lock(struct file *filp, struct file_lock *fl)¶: file byte range unblock lock

Parameters

struct file *filp: The file to apply the unblock to
struct file_lock *fl: The lock to be unblocked

Description

Used by lock managers to cancel blocked requests

int posix_lock_inode_wait(struct inode *inode, struct file_lock *fl)¶: Apply a POSIX-style lock to a file

Parameters

struct inode *inode: inode of file to which lock request should be applied
struct file_lock *fl: The lock to be applied

Description

Apply a POSIX style lock request to an inode.

int locks_mandatory_locked(struct file *file)¶: Check for an active lock

Parameters

struct file *file: the file to check

Description

Searches the inode’s list of locks to find any POSIX locks which conflict. This function is called from locks_verify_locked() only.

int fcntl_getlease(struct file *filp)¶: Enquire what lease is currently active

Parameters

struct file *filp

the file

The value returned by this function will be one of (if no lease break is pending):

F_RDLCK to indicate a shared lease is held.

F_WRLCK to indicate an exclusive lease is held.

F_UNLCK to indicate no lease is held.

(if a lease break is pending):

F_RDLCK to indicate an exclusive lease needs to be: changed to a shared lease (or removed).

F_UNLCK to indicate the lease needs to be removed.

XXX: sfr & willy disagree over whether F_INPROGRESS should be returned to userspace.

int check_conflicting_open(struct file *filp, const long arg, int flags)¶: see if the given file points to an inode that has an existing open that would conflict with the desired lease.

Parameters

struct file *filp: file to check
const long arg: type of lease that we’re trying to acquire
int flags: current lock flags

Description

Check to see if there’s an existing open fd on this file that would conflict with the lease we’re trying to set.

int fcntl_setlease(unsigned int fd, struct file *filp, long arg)¶: sets a lease on an open file

Parameters

unsigned int fd

open file descriptor

struct file *filp

file pointer

long arg

type of lease to obtain

Call this fcntl to establish a lease on the file. Note that you also need to call F_SETSIG to receive a signal when the lease is broken.

int flock_lock_inode_wait(struct inode *inode, struct file_lock *fl)¶: Apply a FLOCK-style lock to a file

Parameters

struct inode *inode: inode of the file to apply to
struct file_lock *fl: The lock to be applied

Description

Apply a FLOCK style lock request to an inode.

long sys_flock(unsigned int fd, unsigned int cmd)¶: flock() system call.

Parameters

unsigned int fd

the file descriptor to lock.

unsigned int cmd

the type of lock to apply.

Apply a FL_FLOCK style lock to an open file descriptor. The cmd can be one of:

LOCK_SH – a shared lock.
LOCK_EX – an exclusive lock.
LOCK_UN – remove an existing lock.
LOCK_MAND – a ‘mandatory’ flock. This exists to emulate Windows Share Modes.

LOCK_MAND can be combined with LOCK_READ or LOCK_WRITE to allow other processes read and write access respectively.

pid_t locks_translate_pid(struct file_lock *fl, struct pid_namespace *ns)¶: translate a file_lock’s fl_pid number into a namespace

Parameters

struct file_lock *fl: The file_lock who’s fl_pid should be translated
struct pid_namespace *ns: The namespace into which the pid should be translated

Description

Used to tranlate a fl_pid into a namespace virtual pid number

Other Functions¶

void mpage_readahead(struct readahead_control *rac, get_block_t get_block)¶: start reads against pages

Parameters

struct readahead_control *rac: Describes which pages to read.
get_block_t get_block: The filesystem’s block mapper function.

Description

This function walks the pages and the blocks within each page, building and emitting large BIOs.

If anything unusual happens, such as:

encountering a page which has buffers
encountering a page which has a non-hole after a hole
encountering a page with non-contiguous blocks

then this code just gives up and calls the buffer_head-based read function. It does handle a page which has holes at the end - that is a common case: the end-of-file on blocksize < PAGE_SIZE setups.

BH_Boundary explanation:

There is a problem. The mpage read code assembles several pages, gets all their disk mappings, and then submits them all. That’s fine, but obtaining the disk mappings may require I/O. Reads of indirect blocks, for example.

So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be submitted in the following order:

12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16

because the indirect block has to be read to get the mappings of blocks 13,14,15,16. Obviously, this impacts performance.

So what we do it to allow the filesystem’s get_block() function to set BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block after this one will require I/O against a block which is probably close to this one. So you should push what I/O you have currently accumulated.

This all causes the disk requests to be issued in the correct order.

int mpage_writepages(struct address_space *mapping, struct writeback_control *wbc, get_block_t get_block)¶: walk the list of dirty pages of the given address space & writepage() all of them

Parameters

struct address_space *mapping: address space structure to write
struct writeback_control *wbc: subtract the number of written pages from *wbc->nr_to_write
get_block_t get_block: the filesystem’s block mapper function. If this is NULL then use a_ops->writepage. Otherwise, go direct-to-BIO.

Description

This is a library function, which implements the writepages() address_space_operation.

If a page is already under I/O, generic_writepages() skips it, even if it’s dirty. This is desirable behaviour for memory-cleaning writeback, but it is INCORRECT for data-integrity system calls such as fsync(). fsync() and msync() need to guarantee that all the data which was dirty at the time the call was made get new I/O started against them. If wbc->sync_mode is WB_SYNC_ALL then we were called for data integrity and we must wait for existing IO to complete.

int generic_permission(struct inode *inode, int mask)¶: check for access rights on a Posix-like filesystem

Parameters

struct inode *inode: inode to check access rights for
int mask: right to check for (MAY_READ, MAY_WRITE, MAY_EXEC, MAY_NOT_BLOCK …)

Description

Used to check for read/write/execute permissions on a file. We use “fsuid” for this, letting us set arbitrary permissions for filesystem access without changing the “normal” uids which are used for other things.

generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk request cannot be satisfied (eg. requires blocking or too much complexity). It would then be called again in ref-walk mode.

int inode_permission(struct inode *inode, int mask)¶: Check for access rights to a given inode

Parameters

struct inode *inode: Inode to check permission on
int mask: Right to check for (MAY_READ, MAY_WRITE, MAY_EXEC)

Description

Check for read/write/execute permissions on an inode. We use fs[ug]id for this, letting us set arbitrary permissions for filesystem access without changing the “normal” UIDs which are used for other things.

When checking for MAY_APPEND, MAY_WRITE must also be set in mask.

void path_get(const struct path *path)¶: get a reference to a path

Parameters

const struct path *path: path to get the reference to

Description

Given a path increment the reference count to the dentry and the vfsmount.

void path_put(const struct path *path)¶: put a reference to a path

Parameters

const struct path *path: path to put the reference to

Description

Given a path decrement the reference count to the dentry and the vfsmount.

int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt, const char *name, unsigned int flags, struct path *path)¶: lookup a file path relative to a dentry-vfsmount pair

Parameters

struct dentry *dentry: pointer to dentry of the base directory
struct vfsmount *mnt: pointer to vfs mount of the base directory
const char *name: pointer to file name
unsigned int flags: lookup flags
struct path *path: pointer to struct path to fill

struct dentry * try_lookup_one_len(const char *name, struct dentry *base, int len)¶: filesystem helper to lookup single pathname component

Parameters

const char *name: pathname component to lookup
struct dentry *base: base directory to lookup from
int len: maximum length len should be interpreted to

Description

Look up a dentry by name in the dcache, returning NULL if it does not currently exist. The function does not try to create a dentry.

Note that this routine is purely a helper for filesystem usage and should not be called by generic code.

The caller must hold base->i_mutex.

struct dentry * lookup_one_len(const char *name, struct dentry *base, int len)¶: filesystem helper to lookup single pathname component

Parameters

const char *name: pathname component to lookup
struct dentry *base: base directory to lookup from
int len: maximum length len should be interpreted to

Description

Note that this routine is purely a helper for filesystem usage and should not be called by generic code.

The caller must hold base->i_mutex.

struct dentry * lookup_one_len_unlocked(const char *name, struct dentry *base, int len)¶: filesystem helper to lookup single pathname component

Parameters

const char *name: pathname component to lookup
struct dentry *base: base directory to lookup from
int len: maximum length len should be interpreted to

Description

Note that this routine is purely a helper for filesystem usage and should not be called by generic code.

Unlike lookup_one_len, it should be called without the parent i_mutex held, and will take the i_mutex itself if necessary.

int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode)¶: unlink a filesystem object

Parameters

struct inode *dir: parent directory
struct dentry *dentry: victim
struct inode **delegated_inode: returns victim inode, if the inode is delegated.

Description

The caller must hold dir->i_mutex.

If vfs_unlink discovers a delegation, it will return -EWOULDBLOCK and return a reference to the inode in delegated_inode. The caller should then break the delegation on that inode and retry. Because breaking a delegation may take a long time, the caller should drop dir->i_mutex before doing so.

Alternatively, a caller may pass NULL for delegated_inode. This may be appropriate for callers that expect the underlying filesystem not to be NFS exported.

int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry, struct inode **delegated_inode)¶: create a new link

Parameters

struct dentry *old_dentry: object to be linked
struct inode *dir: new parent
struct dentry *new_dentry: where to create the new link
struct inode **delegated_inode: returns inode needing a delegation break

Description

The caller must hold dir->i_mutex

If vfs_link discovers a delegation on the to-be-linked file in need of breaking, it will return -EWOULDBLOCK and return a reference to the inode in delegated_inode. The caller should then break the delegation and retry. Because breaking a delegation may take a long time, the caller should drop the i_mutex before doing so.

Alternatively, a caller may pass NULL for delegated_inode. This may be appropriate for callers that expect the underlying filesystem not to be NFS exported.

int vfs_rename(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry, struct inode **delegated_inode, unsigned int flags)¶: rename a filesystem object

Parameters

struct inode *old_dir: parent of source
struct dentry *old_dentry: source
struct inode *new_dir: parent of destination
struct dentry *new_dentry: destination
struct inode **delegated_inode: returns an inode needing a delegation break
unsigned int flags: rename flags

Description

The caller must hold multiple mutexes–see lock_rename()).

If vfs_rename discovers a delegation in need of breaking at either the source or destination, it will return -EWOULDBLOCK and return a reference to the inode in delegated_inode. The caller should then break the delegation and retry. Because breaking a delegation may take a long time, the caller should drop all locks before doing so.

Alternatively, a caller may pass NULL for delegated_inode. This may be appropriate for callers that expect the underlying filesystem not to be NFS exported.

The worst of all namespace operations - renaming directory. “Perverted” doesn’t even start to describe it. Somebody in UCB had a heck of a trip… Problems:

we can get into loop creation.

race potential - two innocent renames can create a loop together. That’s where 4.4 screws up. Current fix: serialization on sb->s_vfs_rename_mutex. We might be more accurate, but that’s another story.

we have to lock _four_ objects - parents and victim (if it exists), and source (if it is not a directory). And that - after we got ->i_mutex on parents (until then we don’t know whether the target exists). Solution: try to be smart with locking order for inodes. We rely on the fact that tree topology may change only under ->s_vfs_rename_mutex _and_ that parent of the object we move will be locked. Thus we can rank directories by the tree (ancestors first) and rank all non-directories after them. That works since everybody except rename does “lock parent, lookup, lock child” and rename is under ->s_vfs_rename_mutex. HOWEVER, it relies on the assumption that any object with ->lookup() has no more than 1 dentry. If “hybrid” objects will ever appear, we’d better make sure that there’s no link(2) for them.

conversion from fhandle to dentry may come in the wrong moment - when we are removing the target. Solution: we will have to grab ->i_mutex in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on ->i_mutex on parents, which works but leads to some truly excessive locking].

int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen)¶: copy symlink body into userspace buffer

Parameters

struct dentry *dentry: dentry on which to get symbolic link
char __user *buffer: user memory pointer
int buflen: size of buffer

Description

Does not touch atime. That’s up to the caller if necessary

Does not call security hook.

const char * vfs_get_link(struct dentry *dentry, struct delayed_call *done)¶: get symlink body

Parameters

struct dentry *dentry: dentry on which to get symbolic link
struct delayed_call *done: caller needs to free returned data with this

Description

Calls security hook and i_op->get_link() on the supplied inode.

It does not touch atime. That’s up to the caller if necessary.

Does not work on “special” symlinks like /proc/$$/fd/N

int sync_mapping_buffers(struct address_space *mapping)¶: write out & wait upon a mapping’s “associated” buffers

Parameters

struct address_space *mapping: the mapping which wants those buffers written

Description

Starts I/O against the buffers at mapping->private_list, and waits upon that I/O.

Basically, this is a convenience function for fsync(). mapping is a file or directory which needs those buffers to be written for a successful fsync().

void mark_buffer_dirty(struct buffer_head *bh)¶: mark a buffer_head as needing writeout

Parameters

struct buffer_head *bh: the buffer_head to mark dirty

Description

mark_buffer_dirty() will set the dirty bit against the buffer, then set its backing page dirty, then tag the page as dirty in the page cache and then attach the address_space’s inode to its superblock’s dirty inode list.

mark_buffer_dirty() is atomic. It takes bh->b_page->mapping->private_lock, i_pages lock and mapping->host->i_lock.

struct buffer_head * __bread_gfp(struct block_device *bdev, sector_t block, unsigned size, gfp_t gfp)¶: reads a specified block and returns the bh

Parameters

struct block_device *bdev

the block_device to read from

sector_t block

number of block

unsigned size

size (in bytes) to read

gfp_t gfp

page allocation flag

Reads a specified block, and returns buffer head that contains it. The page cache can be allocated from non-movable area not to prevent page migration if you set gfp to zero. It returns NULL if the block was unreadable.

void block_invalidatepage(struct page *page, unsigned int offset, unsigned int length)¶: invalidate part or all of a buffer-backed page

Parameters

struct page *page: the page which is affected
unsigned int offset: start of the range to invalidate
unsigned int length: length of the range to invalidate

Description

block_invalidatepage() is called when all or part of the page has become invalidated by a truncate operation.

block_invalidatepage() does not have to release all buffers, but it must ensure that no dirty buffer is left outside offset and that no I/O is underway against any of the blocks which are outside the truncation point. Because the caller is about to free (and possibly reuse) those blocks on-disk.

void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)¶

Parameters

struct block_device *bdev: Block device to clean buffers in
sector_t block: Start of a range of blocks to clean
sector_t len: Number of blocks to clean

Description

We are taking a range of blocks for data and we don’t want writeback of any buffer-cache aliases starting from return from this function and until the moment when something will explicitly mark the buffer dirty (hopefully that will not happen until we will free that block ;-) We don’t even need to mark it not-uptodate - nobody can expect anything from a newly allocated buffer anyway. We used to use unmap_buffer() for such invalidation, but that was wrong. We definitely don’t want to mark the alias unmapped, for example - it would confuse anyone who might pick it with bread() afterwards…

Also.. Note that bforget() doesn’t lock the buffer. So there can be writeout I/O going on against recently-freed buffers. We don’t wait on that I/O in bforget() - it’s more efficient to wait on the I/O only if we really need to. That happens here.

void ll_rw_block(int op, int op_flags, int nr, struct buffer_head *bhs[])¶: level access to block devices (DEPRECATED)

Parameters

int op: whether to READ or WRITE
int op_flags: req_flag_bits
int nr: number of struct buffer_heads in the array
struct buffer_head *bhs[]: array of pointers to struct buffer_head

Description

ll_rw_block() takes an array of pointers to struct buffer_heads, and requests an I/O operation on them, either a REQ_OP_READ or a REQ_OP_WRITE. op_flags contains flags modifying the detailed I/O behavior, most notably REQ_RAHEAD.

This function drops any buffer that it cannot get a lock on (with the BH_Lock state bit), any buffer that appears to be clean when doing a write request, and any buffer that appears to be up-to-date when doing read request. Further it marks as clean buffers that are processed for writing (the buffer cache won’t assume that they are actually clean until the buffer gets unlocked).

ll_rw_block sets b_end_io to simple completion handler that marks the buffer up-to-date (if appropriate), unlocks the buffer and wakes any waiters.

All of the buffers must be for the same device, and must also be a multiple of the current approved size for the device.

int bh_uptodate_or_lock(struct buffer_head *bh)¶: Test whether the buffer is uptodate

Parameters

struct buffer_head *bh: struct buffer_head

Description

Return true if the buffer is up-to-date and false, with the buffer locked, if not.

int bh_submit_read(struct buffer_head *bh)¶: Submit a locked buffer for reading

Parameters

struct buffer_head *bh: struct buffer_head

Description

Returns zero on success and -EIO on error.

void bio_reset(struct bio *bio)¶: reinitialize a bio

Parameters

struct bio *bio: bio to reset

Description

After calling bio_reset(), bio will be in the same state as a freshly allocated bio returned bio bio_alloc_bioset() - the only fields that are preserved are the ones that are initialized by bio_alloc_bioset(). See comment in struct bio.

void bio_chain(struct bio *bio, struct bio *parent)¶: chain bio completions

Parameters

struct bio *bio: the target bio
struct bio *parent: the parent bio of bio

Description

The caller won’t have a bi_end_io called when bio completes - instead, parent’s bi_end_io won’t be called until both parent and bio have completed; the chained bio will also be freed when it completes.

The caller must not set bi_private or bi_end_io in bio.

struct bio * bio_alloc_bioset(gfp_t gfp_mask, unsigned int nr_iovecs, struct bio_set *bs)¶: allocate a bio for I/O

Parameters

gfp_t gfp_mask: the GFP_* mask given to the slab allocator
unsigned int nr_iovecs: number of iovecs to pre-allocate
struct bio_set *bs: the bio_set to allocate from.

Description

If bs is NULL, uses kmalloc() to allocate the bio; else the allocation is backed by the bs’s mempool.

When bs is not NULL, if __GFP_DIRECT_RECLAIM is set then bio_alloc will always be able to allocate a bio. This is due to the mempool guarantees. To make this work, callers must never allocate more than 1 bio at a time from this pool. Callers that need to allocate more than 1 bio must always submit the previously allocated bio for IO before attempting to allocate a new one. Failure to do so can cause deadlocks under memory pressure.

Note that when running under submit_bio_noacct() (i.e. any block driver), bios are not submitted until after you return - see the code in submit_bio_noacct() that converts recursion into iteration, to prevent stack overflows.

This would normally mean allocating multiple bios under submit_bio_noacct() would be susceptible to deadlocks, but we have deadlock avoidance code that resubmits any blocked bios from a rescuer thread.

However, we do not guarantee forward progress for allocations from other mempools. Doing multiple allocations from the same mempool under submit_bio_noacct() should be avoided - instead, use bio_set’s front_pad for per bio allocations.

Return

Pointer to new bio on success, NULL on failure.

void bio_put(struct bio *bio)¶: release a reference to a bio

Parameters

struct bio *bio: bio to release reference to

Description

Put a reference to a struct bio, either one you have gotten with bio_alloc, bio_get or bio_clone_*. The last put of a bio will free it.

void __bio_clone_fast(struct bio *bio, struct bio *bio_src)¶: clone a bio that shares the original bio’s biovec

Parameters

struct bio *bio

destination bio

struct bio *bio_src

bio to clone

Clone a bio. Caller will own the returned bio, but not the actual data it points to. Reference count of returned bio will be one.

Caller must ensure that bio_src is not freed before bio.

struct bio * bio_clone_fast(struct bio *bio, gfp_t gfp_mask, struct bio_set *bs)¶: clone a bio that shares the original bio’s biovec

Parameters

struct bio *bio

bio to clone

gfp_t gfp_mask

allocation priority

struct bio_set *bs

bio_set to allocate from

Like __bio_clone_fast, only also allocates the returned bio

int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page *page, unsigned int len, unsigned int offset)¶: attempt to add page to passthrough bio

Parameters

struct request_queue *q: the target queue
struct bio *bio: destination bio
struct page *page: page to add
unsigned int len: vec entry length
unsigned int offset: vec entry offset

Description

Attempt to add a page to the bio_vec maplist. This can fail for a number of reasons, such as the bio being full or target block device limitations. The target block device must allow bio’s up to PAGE_SIZE, so it is always possible to add a single page to an empty bio.

This should only be used by passthrough bios.

bool __bio_try_merge_page(struct bio *bio, struct page *page, unsigned int len, unsigned int off, bool *same_page)¶: try appending data to an existing bvec.

Parameters

struct bio *bio: destination bio
struct page *page: start page to add
unsigned int len: length of the data to add
unsigned int off: offset of the data relative to page
bool *same_page: return if the segment has been merged inside the same page

Description

Try to add the data at page + off to the last bvec of bio. This is a useful optimisation for file systems with a block size smaller than the page size.

Warn if (len, off) crosses pages in case that same_page is true.

Return true on success or false on failure.

void __bio_add_page(struct bio *bio, struct page *page, unsigned int len, unsigned int off)¶: add page(s) to a bio in a new segment

Parameters

struct bio *bio: destination bio
struct page *page: start page to add
unsigned int len: length of the data to add, may cross pages
unsigned int off: offset of the data relative to page, may cross pages

Description

Add the data at page + off to bio as a new bvec. The caller must ensure that bio has space for another bvec.

int bio_add_page(struct bio *bio, struct page *page, unsigned int len, unsigned int offset)¶: attempt to add page(s) to bio

Parameters

struct bio *bio

destination bio

struct page *page

start page to add

unsigned int len

vec entry length, may cross pages

unsigned int offset

vec entry offset relative to page, may cross pages

Attempt to add page(s) to the bio_vec maplist. This will only fail if either bio->bi_vcnt == bio->bi_max_vecs or it’s a cloned bio.

int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)¶: add user or kernel pages to a bio

Parameters

struct bio *bio: bio to add pages to
struct iov_iter *iter: iov iterator describing the region to be added

Description

This takes either an iterator pointing to user memory, or one pointing to kernel pages (BVEC iterator). If we’re adding user pages, we pin them and map them into the kernel. On IO completion, the caller should put those pages. If we’re adding kernel pages, and the caller told us it’s safe to do so, we just have to add the pages to the bio directly. We don’t grab an extra reference to those pages (the user should already have that), and we don’t put the page on IO completion. The caller needs to check if the bio is flagged BIO_NO_PAGE_REF on IO completion. If it isn’t, then pages should be released.

The function tries, but does not guarantee, to pin as many pages as fit into the bio, or are requested in iter, whatever is smaller. If MM encounters an error pinning the requested pages, it stops. Error is returned only if 0 pages could be pinned.

int submit_bio_wait(struct bio *bio)¶: submit a bio, and wait until it completes

Parameters

struct bio *bio: The struct bio which describes the I/O

Description

Simple wrapper around submit_bio(). Returns 0 on success, or the error from bio_endio() on failure.

WARNING: Unlike to how submit_bio() is usually used, this function does not result in bio reference to be consumed. The caller must drop the reference on his own.

void bio_advance(struct bio *bio, unsigned bytes)¶: increment/complete a bio by some number of bytes

Parameters

struct bio *bio: bio to advance
unsigned bytes: number of bytes to complete

Description

This updates bi_sector, bi_size and bi_idx; if the number of bytes to complete doesn’t align with a bvec boundary, then bv_len and bv_offset will be updated on the last bvec as well.

bio will then represent the remaining, uncompleted portion of the io.

void bio_copy_data(struct bio *dst, struct bio *src)¶: copy contents of data buffers from one bio to another

Parameters

struct bio *dst: destination bio
struct bio *src: source bio

Description

Stops when it reaches the end of either src or dst - that is, copies min(src->bi_size, dst->bi_size) bytes (or the equivalent for lists of bios).

void bio_list_copy_data(struct bio *dst, struct bio *src)¶: copy contents of data buffers from one chain of bios to another

Parameters

struct bio *dst: destination bio list
struct bio *src: source bio list

Description

Stops when it reaches the end of either the src list or dst list - that is, copies min(src->bi_size, dst->bi_size) bytes (or the equivalent for lists of bios).

void bio_endio(struct bio *bio)¶: end I/O on a bio

Parameters

struct bio *bio: bio

Description

bio_endio() will end I/O on the whole bio. bio_endio() is the preferred way to end I/O on a bio. No one should call bi_end_io() directly on a bio unless they own it and thus know that it has an end_io function.

bio_endio() can be called several times on a bio that has been chained using bio_chain(). The ->bi_end_io() function will only be called the last time. At this point the BLK_TA_COMPLETE tracing event will be generated if BIO_TRACE_COMPLETION is set.

struct bio * bio_split(struct bio *bio, int sectors, gfp_t gfp, struct bio_set *bs)¶: split a bio

Parameters

struct bio *bio: bio to split
int sectors: number of sectors to split from the front of bio
gfp_t gfp: gfp mask
struct bio_set *bs: bio set to allocate from

Description

Allocates and returns a new bio which represents sectors from the start of bio, and updates bio to represent the remaining sectors.

Unless this is a discard request the newly allocated bio will point to bio’s bi_io_vec. It is the caller’s responsibility to ensure that neither bio nor bs are freed before the split bio.

void bio_trim(struct bio *bio, int offset, int size)¶: trim a bio

Parameters

struct bio *bio: bio to trim
int offset: number of sectors to trim from the front of bio
int size: size we want to trim bio to, in sectors

int bioset_init(struct bio_set *bs, unsigned int pool_size, unsigned int front_pad, int flags)¶: Initialize a bio_set

Parameters

struct bio_set *bs: pool to initialize
unsigned int pool_size: Number of bio and bio_vecs to cache in the mempool
unsigned int front_pad: Number of bytes to allocate in front of the returned bio
int flags: Flags to modify behavior, currently BIOSET_NEED_BVECS and BIOSET_NEED_RESCUER

Description

Set up a bio_set to be used with bio_alloc_bioset. Allows the caller to ask for a number of bytes to be allocated in front of the bio. Front pad allocation is useful for embedding the bio inside another structure, to avoid allocating extra data to go with the bio. Note that the bio must be embedded at the END of that structure always, or things will break badly. If BIOSET_NEED_BVECS is set in flags, a separate pool will be allocated for allocating iovecs. This pool is not needed e.g. for bio_clone_fast(). If BIOSET_NEED_RESCUER is set, a workqueue is created which can be used to dispatch queued requests when the mempool runs out of space.

int seq_open(struct file *file, const struct seq_operations *op)¶: initialize sequential file

Parameters

struct file *file

file we initialize

const struct seq_operations *op

method table describing the sequence

seq_open() sets file, associating it with a sequence described by op. op->start() sets the iterator up and returns the first element of sequence. op->stop() shuts it down. op->next() returns the next element of sequence. op->show() prints element into the buffer. In case of error ->start() and ->next() return ERR_PTR(error). In the end of sequence they return NULL. ->show() returns 0 in case of success and negative number in case of error. Returning SEQ_SKIP means “discard this element and move on”.

Note

seq_open() will allocate a struct seq_file and store its: pointer in file->private_data. This pointer should not be modified.

ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)¶: ->read() method for sequential files.

Parameters

struct file *file

the file to read from

char __user *buf

the buffer to read to

size_t size

the maximum number of bytes to read

loff_t *ppos

the current position in the file

Ready-made ->f_op->read()

loff_t seq_lseek(struct file *file, loff_t offset, int whence)¶: ->llseek() method for sequential files.

Parameters

struct file *file

the file in question

loff_t offset

new position

int whence

0 for absolute, 1 for relative position

Ready-made ->f_op->llseek()

int seq_release(struct inode *inode, struct file *file)¶: free the structures associated with sequential file.

Parameters

struct inode *inode

its inode

Frees the structures associated with sequential file; can be used as ->f_op->release() if you don’t have private data to destroy.

struct file *file

file in question

void seq_escape(struct seq_file *m, const char *s, const char *esc)¶: print string into buffer, escaping some characters

Parameters

struct seq_file *m

target buffer

const char *s

string

const char *esc

set of characters that need escaping

Puts string into buffer, replacing each occurrence of character from esc with usual octal escape. Use seq_has_overflowed() to check for errors.

char * mangle_path(char *s, const char *p, const char *esc)¶: mangle and copy path to buffer beginning

Parameters

char *s

buffer start

const char *p

beginning of path in above buffer

const char *esc

set of characters that need escaping

Copy the path from p to s, replacing each occurrence of character from esc with usual octal escape. Returns pointer past last written character in s, or NULL in case of failure.

int seq_path(struct seq_file *m, const struct path *path, const char *esc)¶: seq_file interface to print a pathname

Parameters

struct seq_file *m: the seq_file handle
const struct path *path: the struct path to print
const char *esc: set of characters to escape in the output

Description

return the absolute path of ‘path’, as represented by the dentry / mnt pair in the path parameter.

int seq_file_path(struct seq_file *m, struct file *file, const char *esc)¶: seq_file interface to print a pathname of a file

Parameters

struct seq_file *m: the seq_file handle
struct file *file: the struct file to print
const char *esc: set of characters to escape in the output

Description

return the absolute path to the file.

int seq_write(struct seq_file *seq, const void *data, size_t len)¶: write arbitrary data to buffer

Parameters

struct seq_file *seq: seq_file identifying the buffer to which data should be written
const void *data: data address
size_t len: number of bytes

Description

Return 0 on success, non-zero otherwise.

void seq_pad(struct seq_file *m, char c)¶: write padding spaces to buffer

Parameters

struct seq_file *m: seq_file identifying the buffer to which data should be written
char c: the byte to append after padding if non-zero

struct hlist_node * seq_hlist_start(struct hlist_head *head, loff_t pos)¶: start an iteration of a hlist

Parameters

struct hlist_head *head: the head of the hlist
loff_t pos: the start position of the sequence

Description

Called at seq_file->op->start().

struct hlist_node * seq_hlist_start_head(struct hlist_head *head, loff_t pos)¶: start an iteration of a hlist

Parameters

struct hlist_head *head: the head of the hlist
loff_t pos: the start position of the sequence

Description

Called at seq_file->op->start(). Call this function if you want to print a header at the top of the output.

struct hlist_node * seq_hlist_next(void *v, struct hlist_head *head, loff_t *ppos)¶: move to the next position of the hlist

Parameters

void *v: the current iterator
struct hlist_head *head: the head of the hlist
loff_t *ppos: the current position

Description

Called at seq_file->op->next().

struct hlist_node * seq_hlist_start_rcu(struct hlist_head *head, loff_t pos)¶: start an iteration of a hlist protected by RCU

Parameters

struct hlist_head *head: the head of the hlist
loff_t pos: the start position of the sequence

Description

Called at seq_file->op->start().

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().

struct hlist_node * seq_hlist_start_head_rcu(struct hlist_head *head, loff_t pos)¶: start an iteration of a hlist protected by RCU

Parameters

struct hlist_head *head: the head of the hlist
loff_t pos: the start position of the sequence

Description

Called at seq_file->op->start(). Call this function if you want to print a header at the top of the output.

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().

struct hlist_node * seq_hlist_next_rcu(void *v, struct hlist_head *head, loff_t *ppos)¶: move to the next position of the hlist protected by RCU

Parameters

void *v: the current iterator
struct hlist_head *head: the head of the hlist
loff_t *ppos: the current position

Description

Called at seq_file->op->next().

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().

struct hlist_node * seq_hlist_start_percpu(struct hlist_head __percpu *head, int *cpu, loff_t pos)¶: start an iteration of a percpu hlist array

Parameters

struct hlist_head __percpu *head: pointer to percpu array of struct hlist_heads
int *cpu: pointer to cpu “cursor”
loff_t pos: start position of sequence

Description

Called at seq_file->op->start().

struct hlist_node * seq_hlist_next_percpu(void *v, struct hlist_head __percpu *head, int *cpu, loff_t *pos)¶: move to the next position of the percpu hlist array

Parameters

void *v: pointer to current hlist_node
struct hlist_head __percpu *head: pointer to percpu array of struct hlist_heads
int *cpu: pointer to cpu “cursor”
loff_t *pos: start position of sequence

Description

Called at seq_file->op->next().

int register_filesystem(struct file_system_type * fs)¶: register a new filesystem

Parameters

struct file_system_type * fs

the file system structure

Adds the file system passed to the list of file systems the kernel is aware of for mount and other syscalls. Returns 0 on success, or a negative errno code on an error.

The struct file_system_type that is passed is linked into the kernel structures and must not be freed until the file system has been unregistered.

int unregister_filesystem(struct file_system_type * fs)¶: unregister a file system

Parameters

struct file_system_type * fs

filesystem to unregister

Remove a file system that was previously successfully registered with the kernel. An error is returned if the file system is not found. Zero is returned on a success.

Once this function has returned the struct file_system_type structure may be freed or reused.

void wbc_attach_and_unlock_inode(struct writeback_control *wbc, struct inode *inode)¶: associate wbc with target inode and unlock it

Parameters

struct writeback_control *wbc: writeback_control of interest
struct inode *inode: target inode

Description

inode is locked and about to be written back under the control of wbc. Record inode’s writeback context into wbc and unlock the i_lock. On writeback completion, wbc_detach_inode() should be called. This is used to track the cgroup writeback context.

void wbc_detach_inode(struct writeback_control *wbc)¶: disassociate wbc from inode and perform foreign detection

Parameters

struct writeback_control *wbc: writeback_control of the just finished writeback

Description

To be called after a writeback attempt of an inode finishes and undoes wbc_attach_and_unlock_inode(). Can be called under any context.

As concurrent write sharing of an inode is expected to be very rare and memcg only tracks page ownership on first-use basis severely confining the usefulness of such sharing, cgroup writeback tracks ownership per-inode. While the support for concurrent write sharing of an inode is deemed unnecessary, an inode being written to by different cgroups at different points in time is a lot more common, and, more importantly, charging only by first-use can too readily lead to grossly incorrect behaviors (single foreign page can lead to gigabytes of writeback to be incorrectly attributed).

To resolve this issue, cgroup writeback detects the majority dirtier of an inode and transfers the ownership to it. To avoid unnnecessary oscillation, the detection mechanism keeps track of history and gives out the switch verdict only if the foreign usage pattern is stable over a certain amount of time and/or writeback attempts.

On each writeback attempt, wbc tries to detect the majority writer using Boyer-Moore majority vote algorithm. In addition to the byte count from the majority voting, it also counts the bytes written for the current wb and the last round’s winner wb (max of last round’s current wb, the winner from two rounds ago, and the last round’s majority candidate). Keeping track of the historical winner helps the algorithm to semi-reliably detect the most active writer even when it’s not the absolute majority.

Once the winner of the round is determined, whether the winner is foreign or not and how much IO time the round consumed is recorded in inode->i_wb_frn_history. If the amount of recorded foreign IO time is over a certain threshold, the switch verdict is given.

void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page, size_t bytes)¶: account writeback to update inode cgroup ownership

Parameters

struct writeback_control *wbc: writeback_control of the writeback in progress
struct page *page: page being written out
size_t bytes: number of bytes being written out

Description

bytes from page are about to written out during the writeback controlled by wbc. Keep the book for foreign inode detection. See wbc_detach_inode().

int inode_congested(struct inode *inode, int cong_bits)¶: test whether an inode is congested

Parameters

struct inode *inode: inode to test for congestion (may be NULL)
int cong_bits: mask of WB_[a]sync_congested bits to test

Description

Tests whether inode is congested. cong_bits is the mask of congestion bits to test and the return value is the mask of set bits.

If cgroup writeback is enabled for inode, the congestion state is determined by whether the cgwb (cgroup bdi_writeback) for the blkcg associated with inode is congested; otherwise, the root wb’s congestion state is used.

inode is allowed to be NULL as this function is often called on mapping->host which is NULL for the swapper space.

void __mark_inode_dirty(struct inode *inode, int flags)¶: internal function

Parameters

struct inode *inode: inode to mark
int flags: what kind of dirty (i.e. I_DIRTY_SYNC)

Description

Mark an inode as dirty. Callers should use mark_inode_dirty or mark_inode_dirty_sync.

Put the inode on the super block’s dirty list.

CAREFUL! We mark it dirty unconditionally, but move it onto the dirty list only if it is hashed or if it refers to a blockdev. If it was not hashed, it will never be added to the dirty list even if it is later hashed, as it will have been marked dirty already.

In short, make sure you hash any inodes _before_ you start marking them dirty.

Note that for blockdevs, inode->dirtied_when represents the dirtying time of the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of the kernel-internal blockdev inode represents the dirtying time of the blockdev’s pages. This is why for I_DIRTY_PAGES we always use page->mapping->host, so the page-dirtying time is recorded in the internal blockdev inode.

void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr, enum wb_reason reason)¶: writeback dirty inodes from given super_block

Parameters

struct super_block *sb: the superblock
unsigned long nr: the number of pages to write
enum wb_reason reason: reason why some writeback work initiated

Description

Start writeback on some inodes on this super_block. No guarantees are made on how many (if any) will be written, and this function does not wait for IO completion of submitted IO.

void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)¶: writeback dirty inodes from given super_block

Parameters

struct super_block *sb: the superblock
enum wb_reason reason: reason why some writeback work was initiated

Description

Start writeback on some inodes on this super_block. No guarantees are made on how many (if any) will be written, and this function does not wait for IO completion of submitted IO.

void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)¶: try to start writeback if none underway

Parameters

struct super_block *sb: the superblock
enum wb_reason reason: reason why some writeback work was initiated

Description

Invoke __writeback_inodes_sb_nr if no writeback is currently underway.

void sync_inodes_sb(struct super_block *sb)¶: sync sb inode pages

Parameters

struct super_block *sb: the superblock

Description

This function writes and waits on any dirty inode belonging to this super_block.

int write_inode_now(struct inode *inode, int sync)¶: write an inode to disk

Parameters

struct inode *inode: inode to write to disk
int sync: whether the write should be synchronous or not

Description

This function commits an inode to disk immediately if it is dirty. This is primarily needed by knfsd.

The caller must either have a ref on the inode or must have set I_WILL_FREE.

int sync_inode(struct inode *inode, struct writeback_control *wbc)¶: write an inode and its pages to disk.

Parameters

struct inode *inode: the inode to sync
struct writeback_control *wbc: controls the writeback mode

Description

sync_inode() will write an inode and its pages to disk. It will also correctly update the inode on its superblock’s dirty inode lists and will update inode->i_state.

The caller must have a ref on the inode.

int sync_inode_metadata(struct inode *inode, int wait)¶: write an inode to disk

Parameters

struct inode *inode: the inode to sync
int wait: wait for I/O to complete.

Description

Write an inode to disk and adjust its dirty state after completion.

Note

only writes the actual inode, no associated data or other metadata.

int freeze_bdev(struct block_device *bdev)¶

lock a filesystem and force it into a consistent state

Parameters

struct block_device *bdev: blockdevice to lock

Description

If a superblock is found on this device, we take the s_umount semaphore on it to make sure nobody unmounts until the snapshot creation is done. The reference counter (bd_fsfreeze_count) guarantees that only the last unfreeze process can unfreeze the frozen filesystem actually when multiple freeze requests arrive simultaneously. It counts up in freeze_bdev() and count down in thaw_bdev(). When it becomes 0, thaw_bdev() will unfreeze actually.

int thaw_bdev(struct block_device *bdev)¶

unlock filesystem

Parameters

struct block_device *bdev: blockdevice to unlock

Description

Unlocks the filesystem and marks it writeable again after freeze_bdev().

struct block_device * bdgrab(struct block_device *bdev)¶

Grab a reference to an already referenced block device

Parameters

struct block_device *bdev: Block device to grab a reference to.

Description

Returns the block_device with an additional reference when successful, or NULL if the inode is already beeing freed.

int bd_prepare_to_claim(struct block_device *bdev, void *holder)¶: claim a block device

Parameters

struct block_device *bdev: block device of interest
void *holder: holder trying to claim bdev

Description

Claim bdev. This function fails if bdev is already claimed by another holder and waits if another claiming is in progress. return, the caller has ownership of bd_claiming and bd_holder[s].

Return

0 if bdev can be claimed, -EBUSY otherwise.

void bd_abort_claiming(struct block_device *bdev, void *holder)¶: abort claiming of a block device

Parameters

struct block_device *bdev: block device of interest
void *holder: holder that has claimed bdev

Description

Abort claiming of a block device when the exclusive open failed. This can be also used when exclusive open is not actually desired and we just needed to block other exclusive openers for a while.

int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)¶: create symlinks between holding disk and slave bdev

Parameters

struct block_device *bdev: the claimed slave bdev
struct gendisk *disk: the holding disk

Description

DON’T USE THIS UNLESS YOU’RE ALREADY USING IT.

This functions creates the following sysfs symlinks.

from “slaves” directory of the holder disk to the claimed bdev
from “holders” directory of the bdev to the holder disk

For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is passed to bd_link_disk_holder(), then:

/sys/block/dm-0/slaves/sda –> /sys/block/sda /sys/block/sda/holders/dm-0 –> /sys/block/dm-0

The caller must have claimed bdev before calling this function and ensure that both bdev and disk are valid during the creation and lifetime of these symlinks.

Context

Might sleep.

Return

0 on success, -errno on failure.

void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)¶: destroy symlinks created by bd_link_disk_holder()

Parameters

struct block_device *bdev: the calimed slave bdev
struct gendisk *disk: the holding disk

Description

DON’T USE THIS UNLESS YOU’RE ALREADY USING IT.

Context

Might sleep.

struct block_device * blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)¶: open a block device by device number

Parameters

dev_t dev: device number of block device to open
fmode_t mode: FMODE_* mask
void *holder: exclusive holder identifier

Description

Open the block device described by device number dev. If mode includes FMODE_EXCL, the block device is opened with exclusive access. Specifying FMODE_EXCL with a NULL holder is invalid. Exclusive opens may nest for the same holder.

Use this interface ONLY if you really do not have anything better - i.e. when you are behind a truly sucky interface and all you are given is a device number. Everything else should use blkdev_get_by_path().

Context

Might sleep.

Return

Reference to the block_device on success, ERR_PTR(-errno) on failure.

struct block_device * blkdev_get_by_path(const char *path, fmode_t mode, void *holder)¶: open a block device by name

Parameters

const char *path: path to the block device to open
fmode_t mode: FMODE_* mask
void *holder: exclusive holder identifier

Description

Open the block device described by the device file at path. If mode includes FMODE_EXCL, the block device is opened with exclusive access. Specifying FMODE_EXCL with a NULL holder is invalid. Exclusive opens may nest for the same holder.

Context

Might sleep.

Return

Reference to the block_device on success, ERR_PTR(-errno) on failure.

int lookup_bdev(const char *pathname, dev_t *dev)¶: lookup a struct block_device by name

Parameters

const char *pathname: special file representing the block device
dev_t *dev: return value of the block device’s dev_t

Description

Get a reference to the blockdevice at pathname in the current namespace if possible and return it. Return ERR_PTR(error) otherwise.

struct file * anon_inode_getfile(const char *name, const struct file_operations *fops, void *priv, int flags)¶: creates a new file instance by hooking it up to an anonymous inode, and a dentry that describe the “class” of the file

Parameters

const char *name: [in] name of the “class” of the new file
const struct file_operations *fops: [in] file operations for the new file
void *priv: [in] private data for the new file (will be file’s private_data)
int flags: [in] flags

Description

Creates a new file by hooking it on a single inode. This is useful for files that do not need to have a full-fledged inode in order to operate correctly. All the files created with anon_inode_getfile() will share a single inode, hence saving memory and avoiding code duplication for the file/inode/dentry setup. Returns the newly created file* or an error pointer.

int anon_inode_getfd(const char *name, const struct file_operations *fops, void *priv, int flags)¶: creates a new file instance by hooking it up to an anonymous inode, and a dentry that describe the “class” of the file

Parameters

const char *name: [in] name of the “class” of the new file
const struct file_operations *fops: [in] file operations for the new file
void *priv: [in] private data for the new file (will be file’s private_data)
int flags: [in] flags

Description

Creates a new file by hooking it on a single inode. This is useful for files that do not need to have a full-fledged inode in order to operate correctly. All the files created with anon_inode_getfd() will share a single inode, hence saving memory and avoiding code duplication for the file/inode/dentry setup. Returns new descriptor or an error code.

int setattr_prepare(struct dentry *dentry, struct iattr *attr)¶: check if attribute changes to a dentry are allowed

Parameters

struct dentry *dentry: dentry to check
struct iattr *attr: attributes to change

Description

Check if we are allowed to change the attributes contained in attr in the given dentry. This includes the normal unix access permission checks, as well as checks for rlimits and others. The function also clears SGID bit from mode if user is not allowed to set it. Also file capabilities and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.

Should be called as the first thing in ->setattr implementations, possibly after taking additional locks.

int inode_newsize_ok(const struct inode *inode, loff_t offset)¶: may this inode be truncated to a given size

Parameters

const struct inode *inode: the inode to be truncated
loff_t offset: the new size to assign to the inode

Description

inode_newsize_ok must be called with i_mutex held.

inode_newsize_ok will check filesystem limits and ulimits to check that the new inode size is within limits. inode_newsize_ok will also send SIGXFSZ when necessary. Caller must not proceed with inode size change if failure is returned. inode must be a file (not directory), with appropriate permissions to allow truncate (inode_newsize_ok does NOT check these conditions).

Return

0 on success, -ve errno on failure

void setattr_copy(struct inode *inode, const struct iattr *attr)¶: copy simple metadata updates into the generic inode

Parameters

struct inode *inode: the inode to be updated
const struct iattr *attr: the new attributes

Description

setattr_copy must be called with i_mutex held.

setattr_copy updates the inode’s metadata with that specified in attr. Noticeably missing is inode size update, which is more complex as it requires pagecache updates.

The inode is not marked as dirty after this operation. The rationale is that for “simple” filesystems, the struct inode is the inode storage. The caller is free to mark the inode dirty afterwards if needed.

int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)¶: modify attributes of a filesytem object

Parameters

struct dentry * dentry: object affected
struct iattr * attr: new attributes
struct inode **delegated_inode: returns inode, if the inode is delegated

Description

The caller must hold the i_mutex on the affected object.

If notify_change discovers a delegation in need of breaking, it will return -EWOULDBLOCK and return a reference to the inode in delegated_inode. The caller should then break the delegation and retry. Because breaking a delegation may take a long time, the caller should drop the i_mutex before doing so.

Alternatively, a caller may pass NULL for delegated_inode. This may be appropriate for callers that expect the underlying filesystem not to be NFS exported. Also, passing NULL is fine for callers holding the file open for write, as there can be no conflicting delegation in that case.

char * d_path(const struct path *path, char *buf, int buflen)¶: return the path of a dentry

Parameters

const struct path *path: path to report
char *buf: buffer to return value in
int buflen: buffer length

Description

Convert a dentry into an ASCII path name. If the entry has been deleted the string ” (deleted)” is appended. Note that this is ambiguous.

Returns a pointer into the buffer or an error code if the path was too long. Note: Callers should use the returned pointer, not the passed in buffer, to use the name! The implementation often starts at an offset into the buffer, and may leave 0 bytes at the start.

“buflen” should be positive.

struct page * dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end)¶: find first pinned page in mapping

Parameters

struct address_space *mapping: address space to scan for a page with ref count > 1
loff_t start: Starting offset. Page containing ‘start’ is included.
loff_t end: End offset. Page containing ‘end’ is included. If ‘end’ is LLONG_MAX, pages from ‘start’ till the end of file are included.

Description

DAX requires ZONE_DEVICE mapped pages. These pages are never ‘onlined’ to the page allocator so they are considered idle when page->count == 1. A filesystem uses this interface to determine if any page in the mapping is busy, i.e. for DMA, or other get_user_pages() usages.

It is expected that the filesystem is holding locks to block the establishment of new mappings in this address_space. I.e. it expects to be able to run unmap_mapping_range() and subsequently not race mapping_mapped() becoming true.

ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter, const struct iomap_ops *ops)¶: Perform I/O to a DAX file

Parameters

struct kiocb *iocb: The control block for this I/O
struct iov_iter *iter: The addresses to do I/O from or to
const struct iomap_ops *ops: iomap ops passed from the file system

Description

This function performs read and write operations to directly mapped persistent memory. The callers needs to take care of read/write exclusion and evicting any page cache pages in the region under I/O.

vm_fault_t dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size, pfn_t *pfnp, int *iomap_errp, const struct iomap_ops *ops)¶: handle a page fault on a DAX file

Parameters

struct vm_fault *vmf: The description of the fault
enum page_entry_size pe_size: Size of the page to fault in
pfn_t *pfnp: PFN to insert for synchronous faults if fsync is required
int *iomap_errp: Storage for detailed error code in case of error
const struct iomap_ops *ops: Iomap ops passed from the file system

Description

When a page fault occurs, filesystems may call this helper in their fault handler for DAX files. dax_iomap_fault() assumes the caller has done all the necessary locking for page fault to proceed successfully.

vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf, enum page_entry_size pe_size, pfn_t pfn)¶: finish synchronous page fault

Parameters

struct vm_fault *vmf: The description of the fault
enum page_entry_size pe_size: Size of entry to be inserted
pfn_t pfn: PFN to insert

Description

This function ensures that the file range touched by the page fault is stored persistently on the media and handles inserting of appropriate page table entry.

int simple_setattr(struct dentry *dentry, struct iattr *iattr)¶: setattr for simple filesystem

Parameters

struct dentry *dentry: dentry
struct iattr *iattr: iattr structure

Description

Returns 0 on success, -error on failure.

simple_setattr is a simple ->setattr implementation without a proper implementation of size changes.

It can either be used for in-memory filesystems or special files on simple regular filesystems. Anything that needs to change on-disk or wire state on size changes needs its own setattr method.

int simple_write_end(struct file *file, struct address_space *mapping, loff_t pos, unsigned len, unsigned copied, struct page *page, void *fsdata)¶: .write_end helper for non-block-device FSes

Parameters

struct file *file: See .write_end of address_space_operations
struct address_space *mapping: “
loff_t pos: “
unsigned len: “
unsigned copied: “
struct page *page: “
void *fsdata: “

Description

simple_write_end does the minimum needed for updating a page after writing is done. It has the same API signature as the .write_end of address_space_operations vector. So it can just be set onto .write_end for FSes that don’t need any other processing. i_mutex is assumed to be held. Block based filesystems should use generic_write_end(). Use ONLY with simple_readpage()

NOTE

Even though i_size might get updated by this function, mark_inode_dirty is not called, so a filesystem that actually does store data in .write_inode should extend on what’s done here with a call to mark_inode_dirty() in the case that i_size has changed.

ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos, const void *from, size_t available)¶: copy data from the buffer to user space

Parameters

void __user *to: the user space buffer to read to
size_t count: the maximum number of bytes to read
loff_t *ppos: the current position in the buffer
const void *from: the buffer to read from
size_t available: the size of the buffer

Description

The simple_read_from_buffer() function reads up to count bytes from the buffer from at offset ppos into the user space address starting at to.

On success, the number of bytes read is returned and the offset ppos is advanced by this number, or negative value is returned on error.

ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos, const void __user *from, size_t count)¶: copy data from user space to the buffer

Parameters

void *to: the buffer to write to
size_t available: the size of the buffer
loff_t *ppos: the current position in the buffer
const void __user *from: the user space buffer to read from
size_t count: the maximum number of bytes to read

Description

The simple_write_to_buffer() function reads up to count bytes from the user space address starting at from into the buffer to at offset ppos.

On success, the number of bytes written is returned and the offset ppos is advanced by this number, or negative value is returned on error.

ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos, const void *from, size_t available)¶: copy data from the buffer

Parameters

void *to: the kernel space buffer to read to
size_t count: the maximum number of bytes to read
loff_t *ppos: the current position in the buffer
const void *from: the buffer to read from
size_t available: the size of the buffer

Description

The memory_read_from_buffer() function reads up to count bytes from the buffer from at offset ppos into the kernel space address starting at to.

On success, the number of bytes read is returned and the offset ppos is advanced by this number, or negative value is returned on error.

struct dentry * generic_fh_to_dentry(struct super_block *sb, struct fid *fid, int fh_len, int fh_type, struct inode *(*get_inode)(struct super_block *sb, u64 ino, u32 gen))¶: generic helper for the fh_to_dentry export operation

Parameters

struct super_block *sb: filesystem to do the file handle conversion on
struct fid *fid: file handle to convert
int fh_len: length of the file handle in bytes
int fh_type: type of file handle
struct inode *(*get_inode) (struct super_block *sb, u64 ino, u32 gen): filesystem callback to retrieve inode

Description

This function decodes fid as long as it has one of the well-known Linux filehandle types and calls get_inode on it to retrieve the inode for the object specified in the file handle.

struct dentry * generic_fh_to_parent(struct super_block *sb, struct fid *fid, int fh_len, int fh_type, struct inode *(*get_inode)(struct super_block *sb, u64 ino, u32 gen))¶: generic helper for the fh_to_parent export operation

Parameters

struct super_block *sb: filesystem to do the file handle conversion on
struct fid *fid: file handle to convert
int fh_len: length of the file handle in bytes
int fh_type: type of file handle
struct inode *(*get_inode) (struct super_block *sb, u64 ino, u32 gen): filesystem callback to retrieve inode

Description

This function decodes fid as long as it has one of the well-known Linux filehandle types and calls get_inode on it to retrieve the inode for the _parent_ object specified in the file handle if it is specified in the file handle, or NULL otherwise.

int __generic_file_fsync(struct file *file, loff_t start, loff_t end, int datasync)¶: generic fsync implementation for simple filesystems

Parameters

struct file *file: file to synchronize
loff_t start: start offset in bytes
loff_t end: end offset in bytes (inclusive)
int datasync: only synchronize essential metadata if true

Description

This is a generic implementation of the fsync method for simple filesystems which track all non-inode metadata in the buffers list hanging off the address_space structure.

int generic_file_fsync(struct file *file, loff_t start, loff_t end, int datasync)¶: generic fsync implementation for simple filesystems with flush

Parameters

struct file *file: file to synchronize
loff_t start: start offset in bytes
loff_t end: end offset in bytes (inclusive)
int datasync: only synchronize essential metadata if true

int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)¶: Check addressability of file system

Parameters

unsigned blocksize_bits: log of file system block size
u64 num_blocks: number of blocks in file system

Description

Determine whether a file system with num_blocks blocks (and a block size of 2****blocksize_bits**) is addressable by the sector_t and page cache of the system. Return 0 if so and -EFBIG otherwise.

int simple_nosetlease(struct file *filp, long arg, struct file_lock **flp, void **priv)¶: generic helper for prohibiting leases

Parameters

struct file *filp: file pointer
long arg: type of lease to obtain
struct file_lock **flp: new lease supplied for insertion
void **priv: private data for lm_setup operation

Description

Generic helper for filesystems that do not wish to allow leases to be set. All arguments are ignored and it just returns -EINVAL.

const char * simple_get_link(struct dentry *dentry, struct inode *inode, struct delayed_call *done)¶: generic helper to get the target of “fast” symlinks

Parameters

struct dentry *dentry: not used here
struct inode *inode: the symlink inode
struct delayed_call *done: not used here

Description

Generic helper for filesystems to use for symlink inodes where a pointer to the symlink target is stored in ->i_link. NOTE: this isn’t normally called, since as an optimization the path lookup code uses any non-NULL ->i_link directly, without calling ->get_link(). But ->get_link() still must be set, to mark the inode_operations as being for a symlink.

Return

the symlink target

int generic_ci_d_compare(const struct dentry *dentry, unsigned int len, const char *str, const struct qstr *name)¶: generic d_compare implementation for casefolding filesystems

Parameters

const struct dentry *dentry: dentry whose name we are checking against
unsigned int len: len of name of dentry
const char *str: str pointer to name of dentry
const struct qstr *name: Name to compare against

Return

0 if names match, 1 if mismatch, or -ERRNO

int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str)¶: generic d_hash implementation for casefolding filesystems

Parameters

const struct dentry *dentry: dentry of the parent directory
struct qstr *str: qstr of name whose hash we should fill in

Return

0 if hash was successful or unchanged, and -EINVAL on error

void generic_set_encrypted_ci_d_ops(struct dentry *dentry)¶: helper for setting d_ops for given dentry

Parameters

struct dentry *dentry: dentry to set ops on

Description

Casefolded directories need d_hash and d_compare set, so that the dentries contained in them are handled case-insensitively. Note that these operations are needed on the parent directory rather than on the dentries in it, and while the casefolding flag can be toggled on and off on an empty directory, dentry_operations can’t be changed later. As a result, if the filesystem has casefolding support enabled at all, we have to give all dentries the casefolding operations even if their inode doesn’t have the casefolding flag currently (and thus the casefolding ops would be no-ops for now).

Encryption works differently in that the only dentry operation it needs is d_revalidate, which it only needs on dentries that have the no-key name flag. The no-key flag can’t be set “later”, so we don’t have to worry about that.

Finally, to maximize compatibility with overlayfs (which isn’t compatible with certain dentry operations) and to avoid taking an unnecessary performance hit, we use custom dentry_operations for each possible combination rather than always installing all operations.

int posix_acl_update_mode(struct inode *inode, umode_t *mode_p, struct posix_acl **acl)¶: update mode in set_acl

Parameters

struct inode *inode: target inode
umode_t *mode_p: mode (pointer) for update
struct posix_acl **acl: acl pointer

Description

Update the file mode when setting an ACL: compute the new file permission bits based on the ACL. In addition, if the ACL is equivalent to the new file mode, set *acl to NULL to indicate that no ACL should be set.

As with chmod, clear the setgid bit if the caller is not in the owning group or capable of CAP_FSETID (see inode_change_ok).

Called from set_acl inode operations.

void generic_fillattr(struct inode *inode, struct kstat *stat)¶: Fill in the basic attributes from the inode struct

Parameters

struct inode *inode: Inode to use as the source
struct kstat *stat: Where to fill in the attributes

Description

Fill in the basic attributes in the kstat structure from data that’s to be found on the VFS inode structure. This is the default if no getattr inode operation is supplied.

int vfs_getattr_nosec(const struct path *path, struct kstat *stat, u32 request_mask, unsigned int query_flags)¶: getattr without security checks

Parameters

const struct path *path: file to get attributes from
struct kstat *stat: structure to return attributes in
u32 request_mask: STATX_xxx flags indicating what the caller wants
unsigned int query_flags: Query mode (AT_STATX_SYNC_TYPE)

Description

Get attributes without calling security_inode_getattr.

Currently the only caller other than vfs_getattr is internal to the filehandle lookup code, which uses only the inode number and returns no attributes to any user. Any other code probably wants vfs_getattr.

int vfs_fsync_range(struct file *file, loff_t start, loff_t end, int datasync)¶: helper to sync a range of data & metadata to disk

Parameters

struct file *file: file to sync
loff_t start: offset in bytes of the beginning of data range to sync
loff_t end: offset in bytes of the end of data range (inclusive)
int datasync: perform only datasync

Description

Write back data in range start..**end** and metadata for file to disk. If datasync is set only metadata needed to access modified file data is written.

int vfs_fsync(struct file *file, int datasync)¶: perform a fsync or fdatasync on a file

Parameters

struct file *file: file to sync
int datasync: only perform a fdatasync operation

Description

Write back data and metadata for file to disk. If datasync is set only metadata needed to access modified file data is written.

int __vfs_setxattr_locked(struct dentry *dentry, const char *name, const void *value, size_t size, int flags, struct inode **delegated_inode)¶: set an extended attribute while holding the inode lock

Parameters

struct dentry *dentry: object to perform setxattr on
const char *name: xattr name to set
const void *value: value to set name to
size_t size: size of value
int flags: flags to pass into filesystem operations
struct inode **delegated_inode: on return, will contain an inode pointer that a delegation was broken on, NULL if none.

int __vfs_removexattr_locked(struct dentry *dentry, const char *name, struct inode **delegated_inode)¶: set an extended attribute while holding the inode lock

Parameters

struct dentry *dentry: object to perform setxattr on
const char *name: name of xattr to remove
struct inode **delegated_inode: on return, will contain an inode pointer that a delegation was broken on, NULL if none.

const char * xattr_full_name(const struct xattr_handler *handler, const char *name)¶: Compute full attribute name from suffix

Parameters

const struct xattr_handler *handler: handler of the xattr_handler operation
const char *name: name passed to the xattr_handler operation

Description

The get and set xattr handler operations are called with the remainder of the attribute name after skipping the handler’s prefix: for example, “foo” is passed to the get operation of a handler with prefix “user.” to get attribute “user.foo”. The full name is still “there” in the name though.

Note

the list xattr handler operation when called from the vfs is passed a NULL name; some file systems use this operation internally, with varying semantics.

The proc filesystem¶

sysctl interface¶

int proc_dostring(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a string sysctl

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

Reads/writes a string from/to the user buffer. If the kernel buffer provided is not large enough to hold the string, the string is truncated. The copied string is NULL-terminated. If the string is being read by the user process, it is copied and a newline ‘n’ is added. It is truncated if the buffer is not large enough.

Returns 0 on success.

int proc_dointvec(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of integers

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

Reads/writes up to table->maxlen/sizeof(unsigned int) integer values from/to the user buffer, treated as an ASCII string.

Returns 0 on success.

int proc_douintvec(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of unsigned integers

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

Reads/writes up to table->maxlen/sizeof(unsigned int) unsigned integer values from/to the user buffer, treated as an ASCII string.

Returns 0 on success.

int proc_dointvec_minmax(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of integers with min/max values

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

Reads/writes up to table->maxlen/sizeof(unsigned int) integer values from/to the user buffer, treated as an ASCII string.

This routine will ensure the values are within the range specified by table->extra1 (min) and table->extra2 (max).

Returns 0 on success or -EINVAL on write when the range check fails.

int proc_douintvec_minmax(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of unsigned ints with min/max values

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

Reads/writes up to table->maxlen/sizeof(unsigned int) unsigned integer values from/to the user buffer, treated as an ASCII string. Negative strings are not allowed.

This routine will ensure the values are within the range specified by table->extra1 (min) and table->extra2 (max). There is a final sanity check for UINT_MAX to avoid having to support wrap around uses from userspace.

Returns 0 on success or -ERANGE on write when the range check fails.

int proc_doulongvec_minmax(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of long integers with min/max values

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

Reads/writes up to table->maxlen/sizeof(unsigned long) unsigned long values from/to the user buffer, treated as an ASCII string.

This routine will ensure the values are within the range specified by table->extra1 (min) and table->extra2 (max).

Returns 0 on success.

int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of millisecond values with min/max values

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

Reads/writes up to table->maxlen/sizeof(unsigned long) unsigned long values from/to the user buffer, treated as an ASCII string. The values are treated as milliseconds, and converted to jiffies when they are stored.

This routine will ensure the values are within the range specified by table->extra1 (min) and table->extra2 (max).

Returns 0 on success.

int proc_dointvec_jiffies(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of integers as seconds

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

Reads/writes up to table->maxlen/sizeof(unsigned int) integer values from/to the user buffer, treated as an ASCII string. The values read are assumed to be in seconds, and are converted into jiffies.

Returns 0 on success.

int proc_dointvec_userhz_jiffies(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of integers as 1/USER_HZ seconds

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: pointer to the file position

Description

Reads/writes up to table->maxlen/sizeof(unsigned int) integer values from/to the user buffer, treated as an ASCII string. The values read are assumed to be in 1/USER_HZ seconds, and are converted into jiffies.

Returns 0 on success.

int proc_dointvec_ms_jiffies(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read a vector of integers as 1 milliseconds

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: the current position in the file

Description

Reads/writes up to table->maxlen/sizeof(unsigned int) integer values from/to the user buffer, treated as an ASCII string. The values read are assumed to be in 1/1000 seconds, and are converted into jiffies.

Returns 0 on success.

int proc_do_large_bitmap(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos)¶: read/write from/to a large bitmap

Parameters

struct ctl_table *table: the sysctl table
int write: TRUE if this is a write to the sysctl file
void *buffer: the user buffer
size_t *lenp: the size of the user buffer
loff_t *ppos: file position

Description

The bitmap is stored at table->data and the bitmap length (in bits) in table->maxlen.

We use a range comma separated format (e.g. 1,3-4,10-10) so that large bitmaps may be represented in a compact manner. Writing into the file will clear the bitmap then update it with the given input.

Returns 0 on success.

proc filesystem interface¶

void proc_flush_pid(struct pid *pid)¶: Remove dcache entries for pid from the /proc dcache.

Parameters

struct pid *pid: pid that should be flushed.

Description

This function walks a list of inodes (that belong to any proc filesystem) that are attached to the pid and flushes them from the dentry cache.

It is safe and reasonable to cache /proc entries for a task until that task exits. After that they just clog up the dcache with useless entries, possibly causing useful dcache entries to be flushed instead. This routine is provided to flush those useless dcache entries when a process is reaped.

NOTE

This routine is just an optimization so it does not guarantee: that no dcache entries will exist after a process is reaped it just makes it very unlikely that any will persist.

Events based on file descriptors¶

__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)¶: Adds n to the eventfd counter.

Parameters

struct eventfd_ctx *ctx: [in] Pointer to the eventfd context.
__u64 n: [in] Value of the counter to be added to the eventfd internal counter. The value cannot be negative.

Description

This function is supposed to be called by the kernel in paths that do not allow sleeping. In this function we allow the counter to reach the ULLONG_MAX value, and we signal this as overflow condition by returning a EPOLLERR to poll(2).

Returns the amount by which the counter was incremented. This will be less than n if the counter has overflowed.

void eventfd_ctx_put(struct eventfd_ctx *ctx)¶: Releases a reference to the internal eventfd context.

Parameters

struct eventfd_ctx *ctx: [in] Pointer to eventfd context.

Description

The eventfd context reference must have been previously acquired either with eventfd_ctx_fdget() or eventfd_ctx_fileget().

int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *wait, __u64 *cnt)¶: Read the current counter and removes wait queue.

Parameters

struct eventfd_ctx *ctx: [in] Pointer to eventfd context.
wait_queue_entry_t *wait: [in] Wait queue to be removed.
__u64 *cnt: [out] Pointer to the 64-bit counter value.

Description

Returns 0 if successful, or the following error codes:

-EAGAIN

: The operation would have blocked.

This is used to atomically remove a wait queue entry from the eventfd wait queue head, and read/reset the counter value.

struct file * eventfd_fget(int fd)¶: Acquire a reference of an eventfd file descriptor.

Parameters

int fd: [in] Eventfd file descriptor.

Description

Returns a pointer to the eventfd file structure in case of success, or the following error pointer:

`-EBADF`	: Invalid fd file descriptor.
`-EINVAL`	: The fd file descriptor is not an eventfd file.

struct eventfd_ctx * eventfd_ctx_fdget(int fd)¶: Acquires a reference to the internal eventfd context.

Parameters

int fd: [in] Eventfd file descriptor.

Description

Returns a pointer to the internal eventfd context, otherwise the error pointers returned by the following functions:

eventfd_fget

struct eventfd_ctx * eventfd_ctx_fileget(struct file *file)¶: Acquires a reference to the internal eventfd context.

Parameters

struct file *file: [in] Eventfd file pointer.

Description

Returns a pointer to the internal eventfd context, otherwise the error pointer:

-EINVAL

: The fd file descriptor is not an eventfd file.

The Filesystem for Exporting Kernel Objects¶

int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr, const void *ns)¶: create an attribute file for an object with custom ns

Parameters

struct kobject *kobj: object we’re creating for
const struct attribute *attr: attribute descriptor
const void *ns: namespace the new file should belong to

int sysfs_add_file_to_group(struct kobject *kobj, const struct attribute *attr, const char *group)¶: add an attribute file to a pre-existing group.

Parameters

struct kobject *kobj: object we’re acting for.
const struct attribute *attr: attribute descriptor.
const char *group: group name.

int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr, umode_t mode)¶: update the modified mode value on an object attribute.

Parameters

struct kobject *kobj: object we’re acting for.
const struct attribute *attr: attribute descriptor.
umode_t mode: file permissions.

struct kernfs_node * sysfs_break_active_protection(struct kobject *kobj, const struct attribute *attr)¶: break “active” protection

Parameters

struct kobject *kobj: The kernel object attr is associated with.
const struct attribute *attr: The attribute to break the “active” protection for.

Description

With sysfs, just like kernfs, deletion of an attribute is postponed until all active .show() and .store() callbacks have finished unless this function is called. Hence this function is useful in methods that implement self deletion.

void sysfs_unbreak_active_protection(struct kernfs_node *kn)¶: restore “active” protection

Parameters

struct kernfs_node *kn: Pointer returned by sysfs_break_active_protection().

Description

Undo the effects of sysfs_break_active_protection(). Since this function calls kernfs_put() on the kernfs node that corresponds to the ‘attr’ argument passed to sysfs_break_active_protection() that attribute may have been removed between the sysfs_break_active_protection() and sysfs_unbreak_active_protection() calls, it is not safe to access kn after this function has returned.

void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr, const void *ns)¶: remove an object attribute with a custom ns tag

Parameters

struct kobject *kobj: object we’re acting for
const struct attribute *attr: attribute descriptor
const void *ns: namespace tag of the file to remove

Description

Hash the attribute name and namespace tag and kill the victim.

bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr)¶: remove an object attribute from its own method

Parameters

struct kobject *kobj: object we’re acting for
const struct attribute *attr: attribute descriptor

Description

See kernfs_remove_self() for details.

void sysfs_remove_file_from_group(struct kobject *kobj, const struct attribute *attr, const char *group)¶: remove an attribute file from a group.

Parameters

struct kobject *kobj: object we’re acting for.
const struct attribute *attr: attribute descriptor.
const char *group: group name.

int sysfs_create_bin_file(struct kobject *kobj, const struct bin_attribute *attr)¶: create binary file for object.

Parameters

struct kobject *kobj: object.
const struct bin_attribute *attr: attribute descriptor.

void sysfs_remove_bin_file(struct kobject *kobj, const struct bin_attribute *attr)¶: remove binary file for object.

Parameters

struct kobject *kobj: object.
const struct bin_attribute *attr: attribute descriptor.

int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid, kgid_t kgid)¶: change owner of a sysfs file.

Parameters

struct kobject *kobj: object.
const char *name: name of the file to change.
kuid_t kuid: new owner’s kuid
kgid_t kgid: new owner’s kgid

Description

This function looks up the sysfs entry name under kobj and changes the ownership to kuid/kgid.

Returns 0 on success or error code on failure.

int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)¶: change owner of the given object.

Parameters

struct kobject *kobj: object.
kuid_t kuid: new owner’s kuid
kgid_t kgid: new owner’s kgid

Description

Change the owner of the default directory, files, groups, and attributes of kobj to kuid/kgid. Note that sysfs_change_owner mirrors how the sysfs entries for a kobject are added by driver core. In summary, sysfs_change_owner() takes care of the default directory entry for kobj, the default attributes associated with the ktype of kobj and the default attributes associated with the ktype of kobj. Additional properties not added by driver core have to be changed by the driver or subsystem which created them. This is similar to how driver/subsystem specific entries are removed.

Returns 0 on success or error code on failure.

int sysfs_emit(char *buf, const char *fmt, ...)¶: scnprintf equivalent, aware of PAGE_SIZE buffer.

Parameters

char *buf: start of PAGE_SIZE buffer.
const char *fmt: format
...: optional arguments to format

Description

Returns number of characters written to buf.

int sysfs_emit_at(char *buf, int at, const char *fmt, ...)¶: scnprintf equivalent, aware of PAGE_SIZE buffer.

Parameters

char *buf: start of PAGE_SIZE buffer.
int at: offset in buf to start write in bytes at must be >= 0 && < PAGE_SIZE
const char *fmt: format
...: optional arguments to fmt

Description

Returns number of characters written starting at &**buf**[at].

int sysfs_create_link(struct kobject *kobj, struct kobject *target, const char *name)¶: create symlink between two objects.

Parameters

struct kobject *kobj: object whose directory we’re creating the link in.
struct kobject *target: object we’re pointing to.
const char *name: name of the symlink.

int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target, const char *name)¶: create symlink between two objects.

Parameters

struct kobject *kobj

object whose directory we’re creating the link in.

struct kobject *target

object we’re pointing to.

const char *name

name of the symlink.

This function does the same as sysfs_create_link(), but it doesn’t warn if the link already exists.

void sysfs_remove_link(struct kobject *kobj, const char *name)¶: remove symlink in object’s directory.

Parameters

struct kobject *kobj: object we’re acting for.
const char *name: name of the symlink to remove.

int sysfs_rename_link_ns(struct kobject *kobj, struct kobject *targ, const char *old, const char *new, const void *new_ns)¶: rename symlink in object’s directory.

Parameters

struct kobject *kobj

object we’re acting for.

struct kobject *targ

object we’re pointing to.

const char *old

previous name of the symlink.

const char *new

new name of the symlink.

const void *new_ns

new namespace of the symlink.

A helper function for the common rename symlink idiom.

The debugfs filesystem¶

debugfs interface¶

struct dentry * debugfs_lookup(const char *name, struct dentry *parent)¶: look up an existing debugfs file

Parameters

const char *name: a pointer to a string containing the name of the file to look up.
struct dentry *parent: a pointer to the parent dentry of the file.

Description

This function will return a pointer to a dentry if it succeeds. If the file doesn’t exist or an error occurs, NULL will be returned. The returned dentry must be passed to dput() when it is no longer needed.

If debugfs is not enabled in the kernel, the value -ENODEV will be returned.

struct dentry * debugfs_create_file(const char *name, umode_t mode, struct dentry *parent, void *data, const struct file_operations *fops)¶: create a file in the debugfs 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 debugfs 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 is the basic “create a file” function for debugfs. It allows for a wide range of flexibility in creating a file, or a directory (if you want to create a directory, the debugfs_create_dir() function is recommended to be used instead.)

This function will return a pointer to a dentry if it succeeds. This pointer must be passed to the debugfs_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, ERR_PTR(-ERROR) will be returned.

If debugfs is not enabled in the kernel, the value -ENODEV will be returned.

struct dentry * debugfs_create_file_unsafe(const char *name, umode_t mode, struct dentry *parent, void *data, const struct file_operations *fops)¶: create a file in the debugfs 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 debugfs 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

debugfs_create_file_unsafe() is completely analogous to debugfs_create_file(), the only difference being that the fops handed it will not get protected against file removals by the debugfs core.

It is your responsibility to protect your struct file_operation methods against file removals by means of debugfs_file_get() and debugfs_file_put(). ->open() is still protected by debugfs though.

Any struct file_operations defined by means of DEFINE_DEBUGFS_ATTRIBUTE() is protected against file removals and thus, may be used here.

void debugfs_create_file_size(const char *name, umode_t mode, struct dentry *parent, void *data, const struct file_operations *fops, loff_t file_size)¶: create a file in the debugfs 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 debugfs 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.
loff_t file_size: initial file size

Description

This is the basic “create a file” function for debugfs. It allows for a wide range of flexibility in creating a file, or a directory (if you want to create a directory, the debugfs_create_dir() function is recommended to be used instead.)

struct dentry * debugfs_create_dir(const char *name, struct dentry *parent)¶: create a directory in the debugfs 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 debugfs filesystem.

Description

This function creates a directory in debugfs with the given name.

This function will return a pointer to a dentry if it succeeds. This pointer must be passed to the debugfs_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, ERR_PTR(-ERROR) will be returned.

If debugfs is not enabled in the kernel, the value -ENODEV will be returned.

struct dentry * debugfs_create_automount(const char *name, struct dentry *parent, debugfs_automount_t f, void *data)¶: create automount point in the debugfs filesystem

Parameters

const char *name: a pointer to a string containing the name of the file 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 file will be created in the root of the debugfs filesystem.
debugfs_automount_t f: function to be called when pathname resolution steps on that one.
void *data: opaque argument to pass to f().

Description

f should return what ->d_automount() would.

struct dentry * debugfs_create_symlink(const char *name, struct dentry *parent, const char *target)¶: create a symbolic link in the debugfs filesystem

Parameters

const char *name: a pointer to a string containing the name of the symbolic link to create.
struct dentry *parent: a pointer to the parent dentry for this symbolic link. This should be a directory dentry if set. If this parameter is NULL, then the symbolic link will be created in the root of the debugfs filesystem.
const char *target: a pointer to a string containing the path to the target of the symbolic link.

Description

This function creates a symbolic link with the given name in debugfs that links to the given target path.

This function will return a pointer to a dentry if it succeeds. This pointer must be passed to the debugfs_remove() function when the symbolic link is to be removed (no automatic cleanup happens if your module is unloaded, you are responsible here.) If an error occurs, ERR_PTR(-ERROR) will be returned.

If debugfs is not enabled in the kernel, the value -ENODEV will be returned.

void debugfs_remove(struct dentry *dentry)¶: recursively removes a directory

Parameters

struct dentry *dentry: a pointer to a the dentry of the directory to be removed. If this parameter is NULL or an error value, nothing will be done.

Description

This function recursively removes a directory tree in debugfs that was previously created with a call to another debugfs function (like debugfs_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.

struct dentry * debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry, struct dentry *new_dir, const char *new_name)¶: rename a file/directory in the debugfs filesystem

Parameters

struct dentry *old_dir: a pointer to the parent dentry for the renamed object. This should be a directory dentry.
struct dentry *old_dentry: dentry of an object to be renamed.
struct dentry *new_dir: a pointer to the parent dentry where the object should be moved. This should be a directory dentry.
const char *new_name: a pointer to a string containing the target name.

Description

This function renames a file/directory in debugfs. The target must not exist for rename to succeed.

This function will return a pointer to old_dentry (which is updated to reflect renaming) if it succeeds. If an error occurs, NULL will be returned.

If debugfs is not enabled in the kernel, the value -ENODEV will be returned.

bool debugfs_initialized(void)¶: Tells whether debugfs has been registered

Parameters

void: no arguments

int debugfs_file_get(struct dentry *dentry)¶: mark the beginning of file data access

Parameters

struct dentry *dentry: the dentry object whose data is being accessed.

Description

Up to a matching call to debugfs_file_put(), any successive call into the file removing functions debugfs_remove() and debugfs_remove_recursive() will block. Since associated private file data may only get freed after a successful return of any of the removal functions, you may safely access it after a successful call to debugfs_file_get() without worrying about lifetime issues.

If -EIO is returned, the file has already been removed and thus, it is not safe to access any of its data. If, on the other hand, it is allowed to access the file data, zero is returned.

void debugfs_file_put(struct dentry *dentry)¶: mark the end of file data access

Parameters

struct dentry *dentry: the dentry object formerly passed to debugfs_file_get().

Description

Allow any ongoing concurrent call into debugfs_remove() or debugfs_remove_recursive() blocked by a former call to debugfs_file_get() to proceed and return to its caller.

void debugfs_create_u8(const char *name, umode_t mode, struct dentry *parent, u8 *value)¶: create a debugfs file that is used to read and write an unsigned 8-bit value

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 debugfs filesystem.
u8 *value: a pointer to the variable that the file should read to and write from.

Description

This function creates a file in debugfs with the given name that contains the value of the variable value. If the mode variable is so set, it can be read from, and written to.

void debugfs_create_u16(const char *name, umode_t mode, struct dentry *parent, u16 *value)¶: create a debugfs file that is used to read and write an unsigned 16-bit value

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 debugfs filesystem.
u16 *value: a pointer to the variable that the file should read to and write from.

Description

This function creates a file in debugfs with the given name that contains the value of the variable value. If the mode variable is so set, it can be read from, and written to.

void debugfs_create_u32(const char *name, umode_t mode, struct dentry *parent, u32 *value)¶: create a debugfs file that is used to read and write an unsigned 32-bit value

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 debugfs filesystem.
u32 *value: a pointer to the variable that the file should read to and write from.

Description

This function creates a file in debugfs with the given name that contains the value of the variable value. If the mode variable is so set, it can be read from, and written to.

void debugfs_create_u64(const char *name, umode_t mode, struct dentry *parent, u64 *value)¶: create a debugfs file that is used to read and write an unsigned 64-bit value

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 debugfs filesystem.
u64 *value: a pointer to the variable that the file should read to and write from.

Description

This function creates a file in debugfs with the given name that contains the value of the variable value. If the mode variable is so set, it can be read from, and written to.

struct dentry * debugfs_create_ulong(const char *name, umode_t mode, struct dentry *parent, unsigned long *value)¶: create a debugfs file that is used to read and write an unsigned long value.

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 debugfs filesystem.
unsigned long *value: a pointer to the variable that the file should read to and write from.

Description

This function creates a file in debugfs with the given name that contains the value of the variable value. If the mode variable is so set, it can be read from, and written to.

This function will return a pointer to a dentry if it succeeds. This pointer must be passed to the debugfs_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, ERR_PTR(-ERROR) will be returned.

If debugfs is not enabled in the kernel, the value ERR_PTR(-ENODEV) will be returned.

void debugfs_create_x8(const char *name, umode_t mode, struct dentry *parent, u8 *value)¶: create a debugfs file that is used to read and write an unsigned 8-bit value

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 debugfs filesystem.
u8 *value: a pointer to the variable that the file should read to and write from.

void debugfs_create_x16(const char *name, umode_t mode, struct dentry *parent, u16 *value)¶: create a debugfs file that is used to read and write an unsigned 16-bit value

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 debugfs filesystem.
u16 *value: a pointer to the variable that the file should read to and write from.

void debugfs_create_x32(const char *name, umode_t mode, struct dentry *parent, u32 *value)¶: create a debugfs file that is used to read and write an unsigned 32-bit value

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 debugfs filesystem.
u32 *value: a pointer to the variable that the file should read to and write from.

void debugfs_create_x64(const char *name, umode_t mode, struct dentry *parent, u64 *value)¶: create a debugfs file that is used to read and write an unsigned 64-bit value

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 debugfs filesystem.
u64 *value: a pointer to the variable that the file should read to and write from.

void debugfs_create_size_t(const char *name, umode_t mode, struct dentry *parent, size_t *value)¶: create a debugfs file that is used to read and write an size_t value

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 debugfs filesystem.
size_t *value: a pointer to the variable that the file should read to and write from.

void debugfs_create_atomic_t(const char *name, umode_t mode, struct dentry *parent, atomic_t *value)¶: create a debugfs file that is used to read and write an atomic_t value

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 debugfs filesystem.
atomic_t *value: a pointer to the variable that the file should read to and write from.

struct dentry * debugfs_create_bool(const char *name, umode_t mode, struct dentry *parent, bool *value)¶: create a debugfs file that is used to read and write a boolean value

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 debugfs filesystem.
bool *value: a pointer to the variable that the file should read to and write from.

Description

This function creates a file in debugfs with the given name that contains the value of the variable value. If the mode variable is so set, it can be read from, and written to.

This function will return a pointer to a dentry if it succeeds. This pointer must be passed to the debugfs_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, ERR_PTR(-ERROR) will be returned.

If debugfs is not enabled in the kernel, the value ERR_PTR(-ENODEV) will be returned.

struct dentry * debugfs_create_blob(const char *name, umode_t mode, struct dentry *parent, struct debugfs_blob_wrapper *blob)¶: create a debugfs file that is used to read a binary blob

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 debugfs filesystem.
struct debugfs_blob_wrapper *blob: a pointer to a struct debugfs_blob_wrapper which contains a pointer to the blob data and the size of the data.

Description

This function creates a file in debugfs with the given name that exports blob->data as a binary blob. If the mode variable is so set it can be read from. Writing is not supported.

This function will return a pointer to a dentry if it succeeds. This pointer must be passed to the debugfs_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, ERR_PTR(-ERROR) will be returned.

If debugfs is not enabled in the kernel, the value ERR_PTR(-ENODEV) will be returned.

void debugfs_create_u32_array(const char *name, umode_t mode, struct dentry *parent, struct debugfs_u32_array *array)¶: create a debugfs file that is used to read u32 array.

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 debugfs filesystem.
struct debugfs_u32_array *array: wrapper struct containing data pointer and size of the array.

Description

This function creates a file in debugfs with the given name that exports array as data. If the mode variable is so set it can be read from. Writing is not supported. Seek within the file is also not supported. Once array is created its size can not be changed.

void debugfs_print_regs32(struct seq_file *s, const struct debugfs_reg32 *regs, int nregs, void __iomem *base, char *prefix)¶: use seq_print to describe a set of registers

Parameters

struct seq_file *s: the seq_file structure being used to generate output
const struct debugfs_reg32 *regs: an array if struct debugfs_reg32 structures
int nregs: the length of the above array
void __iomem *base: the base address to be used in reading the registers
char *prefix: a string to be prefixed to every output line

Description

This function outputs a text block describing the current values of some 32-bit hardware registers. It is meant to be used within debugfs files based on seq_file that need to show registers, intermixed with other information. The prefix argument may be used to specify a leading string, because some peripherals have several blocks of identical registers, for example configuration of dma channels

void debugfs_create_regset32(const char *name, umode_t mode, struct dentry *parent, struct debugfs_regset32 *regset)¶: create a debugfs file that returns register values

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 debugfs filesystem.
struct debugfs_regset32 *regset: a pointer to a struct debugfs_regset32, which contains a pointer to an array of register definitions, the array size and the base address where the register bank is to be found.

Description

This function creates a file in debugfs with the given name that reports the names and values of a set of 32-bit registers. If the mode variable is so set it can be read from. Writing is not supported.

void debugfs_create_devm_seqfile(struct device *dev, const char *name, struct dentry *parent, int (*read_fn)(struct seq_file *s, void *data))¶: create a debugfs file that is bound to device.

Parameters

struct device *dev: device related to this debugfs file.
const char *name: name of the debugfs file.
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 debugfs filesystem.
int (*read_fn)(struct seq_file *s, void *data): function pointer called to print the seq_file content.