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Commit ee5dc049 authored by Tobin C. Harding's avatar Tobin C. Harding Committed by Jonathan Corbet
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docs: filesystems: vfs: Render method descriptions 

Currently vfs.rst does not render well into HTML the method descriptions
for VFS data structures.  We can improve the HTML output by putting the
description string on a new line following the method name.
Suggested-by: default avatarJonathan Corbet <corbet@lwn.net>
Signed-off-by: default avatarTobin C. Harding <tobin@kernel.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent af96c1e3
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Documentation/filesystems/vfs.rst
View file @ ee5dc049
......@@ -125,35 +125,46 @@ members are defined:
struct lock_class_key s_umount_key;
};
``name``: the name of the filesystem type, such as "ext2", "iso9660",
``name``
the name of the filesystem type, such as "ext2", "iso9660",
"msdos" and so on
``fs_flags``: various flags (i.e. FS_REQUIRES_DEV, FS_NO_DCACHE, etc.)
``fs_flags``
various flags (i.e. FS_REQUIRES_DEV, FS_NO_DCACHE, etc.)
``mount``: the method to call when a new instance of this filesystem should
be mounted
``mount``
the method to call when a new instance of this filesystem should
be mounted
``kill_sb``: the method to call when an instance of this filesystem
should be shut down
``kill_sb``
the method to call when an instance of this filesystem should be
shut down
``owner``: for internal VFS use: you should initialize this to THIS_MODULE in
most cases.
``next``: for internal VFS use: you should initialize this to NULL
``owner``
for internal VFS use: you should initialize this to THIS_MODULE
in most cases.
``next``
for internal VFS use: you should initialize this to NULL
s_lock_key, s_umount_key: lockdep-specific
The mount() method has the following arguments:
``struct file_system_type *fs_type``: describes the filesystem, partly initialized
by the specific filesystem code
``struct file_system_type *fs_type``
describes the filesystem, partly initialized by the specific
filesystem code
``int flags``: mount flags
``int flags``
mount flags
``const char *dev_name``: the device name we are mounting.
``const char *dev_name``
the device name we are mounting.
``void *data``: arbitrary mount options, usually comes as an ASCII
string (see "Mount Options" section)
``void *data``
arbitrary mount options, usually comes as an ASCII string (see
"Mount Options" section)
The mount() method must return the root dentry of the tree requested by
caller. An active reference to its superblock must be grabbed and the
......@@ -178,22 +189,27 @@ implementation.
Usually, a filesystem uses one of the generic mount() implementations
and provides a fill_super() callback instead. The generic variants are:
``mount_bdev``: mount a filesystem residing on a block device
``mount_bdev``
mount a filesystem residing on a block device
``mount_nodev``: mount a filesystem that is not backed by a device
``mount_nodev``
mount a filesystem that is not backed by a device
``mount_single``: mount a filesystem which shares the instance between
all mounts
``mount_single``
mount a filesystem which shares the instance between all mounts
A fill_super() callback implementation has the following arguments:
``struct super_block *sb``: the superblock structure. The callback
must initialize this properly.
``struct super_block *sb``
the superblock structure. The callback must initialize this
properly.
``void *data``: arbitrary mount options, usually comes as an ASCII
string (see "Mount Options" section)
``void *data``
arbitrary mount options, usually comes as an ASCII string (see
"Mount Options" section)
``int silent``: whether or not to be silent on error
``int silent``
whether or not to be silent on error
The Superblock Object
......@@ -240,87 +256,106 @@ noted. This means that most methods can block safely. All methods are
only called from a process context (i.e. not from an interrupt handler
or bottom half).
``alloc_inode``: this method is called by alloc_inode() to allocate memory
for struct inode and initialize it. If this function is not
``alloc_inode``
this method is called by alloc_inode() to allocate memory for
struct inode and initialize it. If this function is not
defined, a simple 'struct inode' is allocated. Normally
alloc_inode will be used to allocate a larger structure which
contains a 'struct inode' embedded within it.
``destroy_inode``: this method is called by destroy_inode() to release
resources allocated for struct inode. It is only required if
``destroy_inode``
this method is called by destroy_inode() to release resources
allocated for struct inode. It is only required if
->alloc_inode was defined and simply undoes anything done by
->alloc_inode.
``dirty_inode``: this method is called by the VFS to mark an inode dirty.
``dirty_inode``
this method is called by the VFS to mark an inode dirty.
``write_inode``: this method is called when the VFS needs to write an
inode to disc. The second parameter indicates whether the write
should be synchronous or not, not all filesystems check this flag.
``write_inode``
this method is called when the VFS needs to write an inode to
disc. The second parameter indicates whether the write should
be synchronous or not, not all filesystems check this flag.
``drop_inode``: called when the last access to the inode is dropped,
with the inode->i_lock spinlock held.
``drop_inode``
called when the last access to the inode is dropped, with the
inode->i_lock spinlock held.
This method should be either NULL (normal UNIX filesystem
semantics) or "generic_delete_inode" (for filesystems that do not
want to cache inodes - causing "delete_inode" to always be
semantics) or "generic_delete_inode" (for filesystems that do
not want to cache inodes - causing "delete_inode" to always be
called regardless of the value of i_nlink)
The "generic_delete_inode()" behavior is equivalent to the
old practice of using "force_delete" in the put_inode() case,
but does not have the races that the "force_delete()" approach
had.
The "generic_delete_inode()" behavior is equivalent to the old
practice of using "force_delete" in the put_inode() case, but
does not have the races that the "force_delete()" approach had.
``delete_inode``: called when the VFS wants to delete an inode
``delete_inode``
called when the VFS wants to delete an inode
``put_super``: called when the VFS wishes to free the superblock
``put_super``
called when the VFS wishes to free the superblock
(i.e. unmount). This is called with the superblock lock held
``sync_fs``: called when VFS is writing out all dirty data associated with
a superblock. The second parameter indicates whether the method
``sync_fs``
called when VFS is writing out all dirty data associated with a
superblock. The second parameter indicates whether the method
should wait until the write out has been completed. Optional.
``freeze_fs``: called when VFS is locking a filesystem and
forcing it into a consistent state. This method is currently
used by the Logical Volume Manager (LVM).
``freeze_fs``
called when VFS is locking a filesystem and forcing it into a
consistent state. This method is currently used by the Logical
Volume Manager (LVM).
``unfreeze_fs``: called when VFS is unlocking a filesystem and making it writable
``unfreeze_fs``
called when VFS is unlocking a filesystem and making it writable
again.
``statfs``: called when the VFS needs to get filesystem statistics.
``statfs``
called when the VFS needs to get filesystem statistics.
``remount_fs``: called when the filesystem is remounted. This is called
with the kernel lock held
``remount_fs``
called when the filesystem is remounted. This is called with
the kernel lock held
``clear_inode``: called then the VFS clears the inode. Optional
``clear_inode``
called then the VFS clears the inode. Optional
``umount_begin``: called when the VFS is unmounting a filesystem.
``umount_begin``
called when the VFS is unmounting a filesystem.
``show_options``: called by the VFS to show mount options for
/proc/<pid>/mounts. (see "Mount Options" section)
``show_options``
called by the VFS to show mount options for /proc/<pid>/mounts.
(see "Mount Options" section)
``quota_read``: called by the VFS to read from filesystem quota file.
``quota_read``
called by the VFS to read from filesystem quota file.
``quota_write``: called by the VFS to write to filesystem quota file.
``quota_write``
called by the VFS to write to filesystem quota file.
``nr_cached_objects``: called by the sb cache shrinking function for the
filesystem to return the number of freeable cached objects it contains.
``nr_cached_objects``
called by the sb cache shrinking function for the filesystem to
return the number of freeable cached objects it contains.
Optional.
``free_cache_objects``: called by the sb cache shrinking function for the
filesystem to scan the number of objects indicated to try to free them.
Optional, but any filesystem implementing this method needs to also
implement ->nr_cached_objects for it to be called correctly.
``free_cache_objects``
called by the sb cache shrinking function for the filesystem to
scan the number of objects indicated to try to free them.
Optional, but any filesystem implementing this method needs to
also implement ->nr_cached_objects for it to be called
correctly.
We can't do anything with any errors that the filesystem might
encountered, hence the void return type. This will never be called if
the VM is trying to reclaim under GFP_NOFS conditions, hence this
method does not need to handle that situation itself.
encountered, hence the void return type. This will never be
called if the VM is trying to reclaim under GFP_NOFS conditions,
hence this method does not need to handle that situation itself.
Implementations must include conditional reschedule calls inside any
scanning loop that is done. This allows the VFS to determine
appropriate scan batch sizes without having to worry about whether
implementations will cause holdoff problems due to large scan batch
sizes.
Implementations must include conditional reschedule calls inside
any scanning loop that is done. This allows the VFS to
determine appropriate scan batch sizes without having to worry
about whether implementations will cause holdoff problems due to
large scan batch sizes.
Whoever sets up the inode is responsible for filling in the "i_op"
field. This is a pointer to a "struct inode_operations" which describes
......@@ -334,23 +369,31 @@ On filesystems that support extended attributes (xattrs), the s_xattr
superblock field points to a NULL-terminated array of xattr handlers.
Extended attributes are name:value pairs.
``name``: Indicates that the handler matches attributes with the specified name
(such as "system.posix_acl_access"); the prefix field must be NULL.
``name``
Indicates that the handler matches attributes with the specified
name (such as "system.posix_acl_access"); the prefix field must
be NULL.
``prefix``: Indicates that the handler matches all attributes with the specified
name prefix (such as "user."); the name field must be NULL.
``prefix``
Indicates that the handler matches all attributes with the
specified name prefix (such as "user."); the name field must be
NULL.
``list``: Determine if attributes matching this xattr handler should be listed
for a particular dentry. Used by some listxattr implementations like
generic_listxattr.
``list``
Determine if attributes matching this xattr handler should be
listed for a particular dentry. Used by some listxattr
implementations like generic_listxattr.
``get``: Called by the VFS to get the value of a particular extended attribute.
This method is called by the getxattr(2) system call.
``get``
Called by the VFS to get the value of a particular extended
attribute. This method is called by the getxattr(2) system
call.
``set``: Called by the VFS to set the value of a particular extended attribute.
When the new value is NULL, called to remove a particular extended
attribute. This method is called by the the setxattr(2) and
removexattr(2) system calls.
``set``
Called by the VFS to set the value of a particular extended
attribute. When the new value is NULL, called to remove a
particular extended attribute. This method is called by the the
setxattr(2) and removexattr(2) system calls.
When none of the xattr handlers of a filesystem match the specified
attribute name or when a filesystem doesn't support extended attributes,
......@@ -399,128 +442,147 @@ As of kernel 2.6.22, the following members are defined:
Again, all methods are called without any locks being held, unless
otherwise noted.
``create``: called by the open(2) and creat(2) system calls. Only
required if you want to support regular files. The dentry you
get should not have an inode (i.e. it should be a negative
dentry). Here you will probably call d_instantiate() with the
dentry and the newly created inode
``create``
called by the open(2) and creat(2) system calls. Only required
if you want to support regular files. The dentry you get should
not have an inode (i.e. it should be a negative dentry). Here
you will probably call d_instantiate() with the dentry and the
newly created inode
``lookup``: called when the VFS needs to look up an inode in a parent
``lookup``
called when the VFS needs to look up an inode in a parent
directory. The name to look for is found in the dentry. This
method must call d_add() to insert the found inode into the
dentry. The "i_count" field in the inode structure should be
incremented. If the named inode does not exist a NULL inode
should be inserted into the dentry (this is called a negative
dentry). Returning an error code from this routine must only
be done on a real error, otherwise creating inodes with system
dentry). Returning an error code from this routine must only be
done on a real error, otherwise creating inodes with system
calls like create(2), mknod(2), mkdir(2) and so on will fail.
If you wish to overload the dentry methods then you should
initialise the "d_dop" field in the dentry; this is a pointer
to a struct "dentry_operations".
This method is called with the directory inode semaphore held
initialise the "d_dop" field in the dentry; this is a pointer to
a struct "dentry_operations". This method is called with the
directory inode semaphore held
``link``: called by the link(2) system call. Only required if you want
to support hard links. You will probably need to call
``link``
called by the link(2) system call. Only required if you want to
support hard links. You will probably need to call
d_instantiate() just as you would in the create() method
``unlink``: called by the unlink(2) system call. Only required if you
want to support deleting inodes
``unlink``
called by the unlink(2) system call. Only required if you want
to support deleting inodes
``symlink``: called by the symlink(2) system call. Only required if you
want to support symlinks. You will probably need to call
``symlink``
called by the symlink(2) system call. Only required if you want
to support symlinks. You will probably need to call
d_instantiate() just as you would in the create() method
``mkdir``: called by the mkdir(2) system call. Only required if you want
``mkdir``
called by the mkdir(2) system call. Only required if you want
to support creating subdirectories. You will probably need to
call d_instantiate() just as you would in the create() method
``rmdir``: called by the rmdir(2) system call. Only required if you want
``rmdir``
called by the rmdir(2) system call. Only required if you want
to support deleting subdirectories
``mknod``: called by the mknod(2) system call to create a device (char,
block) inode or a named pipe (FIFO) or socket. Only required
if you want to support creating these types of inodes. You
will probably need to call d_instantiate() just as you would
in the create() method
``mknod``
called by the mknod(2) system call to create a device (char,
block) inode or a named pipe (FIFO) or socket. Only required if
you want to support creating these types of inodes. You will
probably need to call d_instantiate() just as you would in the
create() method
``rename``: called by the rename(2) system call to rename the object to
have the parent and name given by the second inode and dentry.
``rename``
called by the rename(2) system call to rename the object to have
the parent and name given by the second inode and dentry.
The filesystem must return -EINVAL for any unsupported or
unknown flags. Currently the following flags are implemented:
(1) RENAME_NOREPLACE: this flag indicates that if the target
of the rename exists the rename should fail with -EEXIST
instead of replacing the target. The VFS already checks for
existence, so for local filesystems the RENAME_NOREPLACE
implementation is equivalent to plain rename.
unknown flags. Currently the following flags are implemented:
(1) RENAME_NOREPLACE: this flag indicates that if the target of
the rename exists the rename should fail with -EEXIST instead of
replacing the target. The VFS already checks for existence, so
for local filesystems the RENAME_NOREPLACE implementation is
equivalent to plain rename.
(2) RENAME_EXCHANGE: exchange source and target. Both must
exist; this is checked by the VFS. Unlike plain rename,
source and target may be of different type.
``get_link``: called by the VFS to follow a symbolic link to the
inode it points to. Only required if you want to support
symbolic links. This method returns the symlink body
to traverse (and possibly resets the current position with
nd_jump_link()). If the body won't go away until the inode
is gone, nothing else is needed; if it needs to be otherwise
pinned, arrange for its release by having get_link(..., ..., done)
do set_delayed_call(done, destructor, argument).
In that case destructor(argument) will be called once VFS is
done with the body you've returned.
May be called in RCU mode; that is indicated by NULL dentry
exist; this is checked by the VFS. Unlike plain rename, source
and target may be of different type.
``get_link``
called by the VFS to follow a symbolic link to the inode it
points to. Only required if you want to support symbolic links.
This method returns the symlink body to traverse (and possibly
resets the current position with nd_jump_link()). If the body
won't go away until the inode is gone, nothing else is needed;
if it needs to be otherwise pinned, arrange for its release by
having get_link(..., ..., done) do set_delayed_call(done,
destructor, argument). In that case destructor(argument) will
be called once VFS is done with the body you've returned. May
be called in RCU mode; that is indicated by NULL dentry
argument. If request can't be handled without leaving RCU mode,
have it return ERR_PTR(-ECHILD).
If the filesystem stores the symlink target in ->i_link, the
VFS may use it directly without calling ->get_link(); however,
->get_link() must still be provided. ->i_link must not be
freed until after an RCU grace period. Writing to ->i_link
post-iget() time requires a 'release' memory barrier.
``readlink``: this is now just an override for use by readlink(2) for the
``readlink``
this is now just an override for use by readlink(2) for the
cases when ->get_link uses nd_jump_link() or object is not in
fact a symlink. Normally filesystems should only implement
->get_link for symlinks and readlink(2) will automatically use
that.
``permission``: called by the VFS to check for access rights on a POSIX-like
``permission``
called by the VFS to check for access rights on a POSIX-like
filesystem.
May be called in rcu-walk mode (mask & MAY_NOT_BLOCK). If in rcu-walk
mode, the filesystem must check the permission without blocking or
storing to the inode.
May be called in rcu-walk mode (mask & MAY_NOT_BLOCK). If in
rcu-walk mode, the filesystem must check the permission without
blocking or storing to the inode.
If a situation is encountered that rcu-walk cannot handle, return
If a situation is encountered that rcu-walk cannot handle,
return
-ECHILD and it will be called again in ref-walk mode.
``setattr``: called by the VFS to set attributes for a file. This method
is called by chmod(2) and related system calls.
``getattr``: called by the VFS to get attributes of a file. This method
is called by stat(2) and related system calls.
``listxattr``: called by the VFS to list all extended attributes for a
given file. This method is called by the listxattr(2) system call.
``update_time``: called by the VFS to update a specific time or the i_version of
an inode. If this is not defined the VFS will update the inode itself
and call mark_inode_dirty_sync.
``atomic_open``: called on the last component of an open. Using this optional
method the filesystem can look up, possibly create and open the file in
one atomic operation. If it wants to leave actual opening to the
caller (e.g. if the file turned out to be a symlink, device, or just
something filesystem won't do atomic open for), it may signal this by
returning finish_no_open(file, dentry). This method is only called if
the last component is negative or needs lookup. Cached positive dentries
are still handled by f_op->open(). If the file was created,
FMODE_CREATED flag should be set in file->f_mode. In case of O_EXCL
the method must only succeed if the file didn't exist and hence FMODE_CREATED
shall always be set on success.
``tmpfile``: called in the end of O_TMPFILE open(). Optional, equivalent to
atomically creating, opening and unlinking a file in given directory.
``setattr``
called by the VFS to set attributes for a file. This method is
called by chmod(2) and related system calls.
``getattr``
called by the VFS to get attributes of a file. This method is
called by stat(2) and related system calls.
``listxattr``
called by the VFS to list all extended attributes for a given
file. This method is called by the listxattr(2) system call.
``update_time``
called by the VFS to update a specific time or the i_version of
an inode. If this is not defined the VFS will update the inode
itself and call mark_inode_dirty_sync.
``atomic_open``
called on the last component of an open. Using this optional
method the filesystem can look up, possibly create and open the
file in one atomic operation. If it wants to leave actual
opening to the caller (e.g. if the file turned out to be a
symlink, device, or just something filesystem won't do atomic
open for), it may signal this by returning finish_no_open(file,
dentry). This method is only called if the last component is
negative or needs lookup. Cached positive dentries are still
handled by f_op->open(). If the file was created, FMODE_CREATED
flag should be set in file->f_mode. In case of O_EXCL the
method must only succeed if the file didn't exist and hence
FMODE_CREATED shall always be set on success.
``tmpfile``
called in the end of O_TMPFILE open(). Optional, equivalent to
atomically creating, opening and unlinking a file in given
directory.
The Address Space Object
......@@ -673,70 +735,75 @@ cache in your filesystem. The following members are defined:
int (*swap_deactivate)(struct file *);
};
``writepage``: called by the VM to write a dirty page to backing store.
This may happen for data integrity reasons (i.e. 'sync'), or
to free up memory (flush). The difference can be seen in
wbc->sync_mode.
The PG_Dirty flag has been cleared and PageLocked is true.
writepage should start writeout, should set PG_Writeback,
and should make sure the page is unlocked, either synchronously
or asynchronously when the write operation completes.
If wbc->sync_mode is WB_SYNC_NONE, ->writepage doesn't have to
try too hard if there are problems, and may choose to write out
other pages from the mapping if that is easier (e.g. due to
internal dependencies). If it chooses not to start writeout, it
should return AOP_WRITEPAGE_ACTIVATE so that the VM will not keep
calling ->writepage on that page.
See the file "Locking" for more details.
``readpage``: called by the VM to read a page from backing store.
The page will be Locked when readpage is called, and should be
unlocked and marked uptodate once the read completes.
If ->readpage discovers that it needs to unlock the page for
some reason, it can do so, and then return AOP_TRUNCATED_PAGE.
In this case, the page will be relocated, relocked and if
that all succeeds, ->readpage will be called again.
``writepages``: called by the VM to write out pages associated with the
``writepage``
called by the VM to write a dirty page to backing store. This
may happen for data integrity reasons (i.e. 'sync'), or to free
up memory (flush). The difference can be seen in
wbc->sync_mode. The PG_Dirty flag has been cleared and
PageLocked is true. writepage should start writeout, should set
PG_Writeback, and should make sure the page is unlocked, either
synchronously or asynchronously when the write operation
completes.
If wbc->sync_mode is WB_SYNC_NONE, ->writepage doesn't have to
try too hard if there are problems, and may choose to write out
other pages from the mapping if that is easier (e.g. due to
internal dependencies). If it chooses not to start writeout, it
should return AOP_WRITEPAGE_ACTIVATE so that the VM will not
keep calling ->writepage on that page.
See the file "Locking" for more details.
``readpage``
called by the VM to read a page from backing store. The page
will be Locked when readpage is called, and should be unlocked
and marked uptodate once the read completes. If ->readpage
discovers that it needs to unlock the page for some reason, it
can do so, and then return AOP_TRUNCATED_PAGE. In this case,
the page will be relocated, relocked and if that all succeeds,
->readpage will be called again.
``writepages``
called by the VM to write out pages associated with the
address_space object. If wbc->sync_mode is WBC_SYNC_ALL, then
the writeback_control will specify a range of pages that must be
written out. If it is WBC_SYNC_NONE, then a nr_to_write is given
and that many pages should be written if possible.
If no ->writepages is given, then mpage_writepages is used
instead. This will choose pages from the address space that are
tagged as DIRTY and will pass them to ->writepage.
``set_page_dirty``: called by the VM to set a page dirty.
This is particularly needed if an address space attaches
private data to a page, and that data needs to be updated when
a page is dirtied. This is called, for example, when a memory
mapped page gets modified.
written out. If it is WBC_SYNC_NONE, then a nr_to_write is
given and that many pages should be written if possible. If no
->writepages is given, then mpage_writepages is used instead.
This will choose pages from the address space that are tagged as
DIRTY and will pass them to ->writepage.
``set_page_dirty``
called by the VM to set a page dirty. This is particularly
needed if an address space attaches private data to a page, and
that data needs to be updated when a page is dirtied. This is
called, for example, when a memory mapped page gets modified.
If defined, it should set the PageDirty flag, and the
PAGECACHE_TAG_DIRTY tag in the radix tree.
``readpages``: called by the VM to read pages associated with the address_space
object. This is essentially just a vector version of
readpage. Instead of just one page, several pages are
requested.
``readpages``
called by the VM to read pages associated with the address_space
object. This is essentially just a vector version of readpage.
Instead of just one page, several pages are requested.
readpages is only used for read-ahead, so read errors are
ignored. If anything goes wrong, feel free to give up.
``write_begin``:
Called by the generic buffered write code to ask the filesystem to
prepare to write len bytes at the given offset in the file. The
address_space should check that the write will be able to complete,
by allocating space if necessary and doing any other internal
housekeeping. If the write will update parts of any basic-blocks on
storage, then those blocks should be pre-read (if they haven't been
read already) so that the updated blocks can be written out properly.
``write_begin``
Called by the generic buffered write code to ask the filesystem
to prepare to write len bytes at the given offset in the file.
The address_space should check that the write will be able to
complete, by allocating space if necessary and doing any other
internal housekeeping. If the write will update parts of any
basic-blocks on storage, then those blocks should be pre-read
(if they haven't been read already) so that the updated blocks
can be written out properly.
The filesystem must return the locked pagecache page for the specified
offset, in ``*pagep``, for the caller to write into.
The filesystem must return the locked pagecache page for the
specified offset, in ``*pagep``, for the caller to write into.
It must be able to cope with short writes (where the length passed to
write_begin is greater than the number of bytes copied into the page).
It must be able to cope with short writes (where the length
passed to write_begin is greater than the number of bytes copied
into the page).
flags is a field for AOP_FLAG_xxx flags, described in
include/linux/fs.h.
......@@ -744,114 +811,128 @@ cache in your filesystem. The following members are defined:
A void * may be returned in fsdata, which then gets passed into
write_end.
Returns 0 on success; < 0 on failure (which is the error code), in
which case write_end is not called.
``write_end``: After a successful write_begin, and data copy, write_end must
be called. len is the original len passed to write_begin, and copied
is the amount that was able to be copied.
The filesystem must take care of unlocking the page and releasing it
refcount, and updating i_size.
Returns < 0 on failure, otherwise the number of bytes (<= 'copied')
that were able to be copied into pagecache.
``bmap``: called by the VFS to map a logical block offset within object to
physical block number. This method is used by the FIBMAP
ioctl and for working with swap-files. To be able to swap to
a file, the file must have a stable mapping to a block
device. The swap system does not go through the filesystem
but instead uses bmap to find out where the blocks in the file
are and uses those addresses directly.
``invalidatepage``: If a page has PagePrivate set, then invalidatepage
will be called when part or all of the page is to be removed
from the address space. This generally corresponds to either a
truncation, punch hole or a complete invalidation of the address
Returns 0 on success; < 0 on failure (which is the error code),
in which case write_end is not called.
``write_end``
After a successful write_begin, and data copy, write_end must be
called. len is the original len passed to write_begin, and
copied is the amount that was able to be copied.
The filesystem must take care of unlocking the page and
releasing it refcount, and updating i_size.
Returns < 0 on failure, otherwise the number of bytes (<=
'copied') that were able to be copied into pagecache.
``bmap``
called by the VFS to map a logical block offset within object to
physical block number. This method is used by the FIBMAP ioctl
and for working with swap-files. To be able to swap to a file,
the file must have a stable mapping to a block device. The swap
system does not go through the filesystem but instead uses bmap
to find out where the blocks in the file are and uses those
addresses directly.
``invalidatepage``
If a page has PagePrivate set, then invalidatepage will be
called when part or all of the page is to be removed from the
address space. This generally corresponds to either a
truncation, punch hole or a complete invalidation of the address
space (in the latter case 'offset' will always be 0 and 'length'
will be PAGE_SIZE). Any private data associated with the page
should be updated to reflect this truncation. If offset is 0 and
length is PAGE_SIZE, then the private data should be released,
because the page must be able to be completely discarded. This may
be done by calling the ->releasepage function, but in this case the
release MUST succeed.
``releasepage``: releasepage is called on PagePrivate pages to indicate
that the page should be freed if possible. ->releasepage
should remove any private data from the page and clear the
PagePrivate flag. If releasepage() fails for some reason, it must
indicate failure with a 0 return value.
releasepage() is used in two distinct though related cases. The
first is when the VM finds a clean page with no active users and
wants to make it a free page. If ->releasepage succeeds, the
page will be removed from the address_space and become free.
should be updated to reflect this truncation. If offset is 0
and length is PAGE_SIZE, then the private data should be
released, because the page must be able to be completely
discarded. This may be done by calling the ->releasepage
function, but in this case the release MUST succeed.
``releasepage``
releasepage is called on PagePrivate pages to indicate that the
page should be freed if possible. ->releasepage should remove
any private data from the page and clear the PagePrivate flag.
If releasepage() fails for some reason, it must indicate failure
with a 0 return value. releasepage() is used in two distinct
though related cases. The first is when the VM finds a clean
page with no active users and wants to make it a free page. If
->releasepage succeeds, the page will be removed from the
address_space and become free.
The second case is when a request has been made to invalidate
some or all pages in an address_space. This can happen
through the fadvise(POSIX_FADV_DONTNEED) system call or by the
filesystem explicitly requesting it as nfs and 9fs do (when
they believe the cache may be out of date with storage) by
calling invalidate_inode_pages2().
If the filesystem makes such a call, and needs to be certain
that all pages are invalidated, then its releasepage will
need to ensure this. Possibly it can clear the PageUptodate
bit if it cannot free private data yet.
``freepage``: freepage is called once the page is no longer visible in
the page cache in order to allow the cleanup of any private
data. Since it may be called by the memory reclaimer, it
should not assume that the original address_space mapping still
exists, and it should not block.
``direct_IO``: called by the generic read/write routines to perform
direct_IO - that is IO requests which bypass the page cache
and transfer data directly between the storage and the
application's address space.
``isolate_page``: Called by the VM when isolating a movable non-lru page.
If page is successfully isolated, VM marks the page as PG_isolated
via __SetPageIsolated.
``migrate_page``: This is used to compact the physical memory usage.
If the VM wants to relocate a page (maybe off a memory card
that is signalling imminent failure) it will pass a new page
and an old page to this function. migrate_page should
transfer any private data across and update any references
that it has to the page.
``putback_page``: Called by the VM when isolated page's migration fails.
``launder_page``: Called before freeing a page - it writes back the dirty page. To
prevent redirtying the page, it is kept locked during the whole
operation.
``is_partially_uptodate``: Called by the VM when reading a file through the
pagecache when the underlying blocksize != pagesize. If the required
block is up to date then the read can complete without needing the IO
to bring the whole page up to date.
``is_dirty_writeback``: Called by the VM when attempting to reclaim a page.
The VM uses dirty and writeback information to determine if it needs
to stall to allow flushers a chance to complete some IO. Ordinarily
it can use PageDirty and PageWriteback but some filesystems have
more complex state (unstable pages in NFS prevent reclaim) or
do not set those flags due to locking problems. This callback
allows a filesystem to indicate to the VM if a page should be
treated as dirty or writeback for the purposes of stalling.
``error_remove_page``: normally set to generic_error_remove_page if truncation
is ok for this address space. Used for memory failure handling.
some or all pages in an address_space. This can happen through
the fadvise(POSIX_FADV_DONTNEED) system call or by the
filesystem explicitly requesting it as nfs and 9fs do (when they
believe the cache may be out of date with storage) by calling
invalidate_inode_pages2(). If the filesystem makes such a call,
and needs to be certain that all pages are invalidated, then its
releasepage will need to ensure this. Possibly it can clear the
PageUptodate bit if it cannot free private data yet.
``freepage``
freepage is called once the page is no longer visible in the
page cache in order to allow the cleanup of any private data.
Since it may be called by the memory reclaimer, it should not
assume that the original address_space mapping still exists, and
it should not block.
``direct_IO``
called by the generic read/write routines to perform direct_IO -
that is IO requests which bypass the page cache and transfer
data directly between the storage and the application's address
space.
``isolate_page``
Called by the VM when isolating a movable non-lru page. If page
is successfully isolated, VM marks the page as PG_isolated via
__SetPageIsolated.
``migrate_page``
This is used to compact the physical memory usage. If the VM
wants to relocate a page (maybe off a memory card that is
signalling imminent failure) it will pass a new page and an old
page to this function. migrate_page should transfer any private
data across and update any references that it has to the page.
``putback_page``
Called by the VM when isolated page's migration fails.
``launder_page``
Called before freeing a page - it writes back the dirty page.
To prevent redirtying the page, it is kept locked during the
whole operation.
``is_partially_uptodate``
Called by the VM when reading a file through the pagecache when
the underlying blocksize != pagesize. If the required block is
up to date then the read can complete without needing the IO to
bring the whole page up to date.
``is_dirty_writeback``
Called by the VM when attempting to reclaim a page. The VM uses
dirty and writeback information to determine if it needs to
stall to allow flushers a chance to complete some IO.
Ordinarily it can use PageDirty and PageWriteback but some
filesystems have more complex state (unstable pages in NFS
prevent reclaim) or do not set those flags due to locking
problems. This callback allows a filesystem to indicate to the
VM if a page should be treated as dirty or writeback for the
purposes of stalling.
``error_remove_page``
normally set to generic_error_remove_page if truncation is ok
for this address space. Used for memory failure handling.
Setting this implies you deal with pages going away under you,
unless you have them locked or reference counts increased.
``swap_activate``: Called when swapon is used on a file to allocate
space if necessary and pin the block lookup information in
memory. A return value of zero indicates success,
in which case this file can be used to back swapspace.
``swap_activate``
Called when swapon is used on a file to allocate space if
necessary and pin the block lookup information in memory. A
return value of zero indicates success, in which case this file
can be used to back swapspace.
``swap_deactivate``: Called during swapoff on files where swap_activate
was successful.
``swap_deactivate``
Called during swapoff on files where swap_activate was
successful.
The File Object
......@@ -912,91 +993,120 @@ This describes how the VFS can manipulate an open file. As of kernel
Again, all methods are called without any locks being held, unless
otherwise noted.
``llseek``: called when the VFS needs to move the file position index
``llseek``
called when the VFS needs to move the file position index
``read``: called by read(2) and related system calls
``read``
called by read(2) and related system calls
``read_iter``: possibly asynchronous read with iov_iter as destination
``read_iter``
possibly asynchronous read with iov_iter as destination
``write``: called by write(2) and related system calls
``write``
called by write(2) and related system calls
``write_iter``: possibly asynchronous write with iov_iter as source
``write_iter``
possibly asynchronous write with iov_iter as source
``iopoll``: called when aio wants to poll for completions on HIPRI iocbs
``iopoll``
called when aio wants to poll for completions on HIPRI iocbs
``iterate``: called when the VFS needs to read the directory contents
``iterate``
called when the VFS needs to read the directory contents
``iterate_shared``: called when the VFS needs to read the directory contents
when filesystem supports concurrent dir iterators
``iterate_shared``
called when the VFS needs to read the directory contents when
filesystem supports concurrent dir iterators
``poll``: called by the VFS when a process wants to check if there is
``poll``
called by the VFS when a process wants to check if there is
activity on this file and (optionally) go to sleep until there
is activity. Called by the select(2) and poll(2) system calls
``unlocked_ioctl``: called by the ioctl(2) system call.
``unlocked_ioctl``
called by the ioctl(2) system call.
``compat_ioctl``: called by the ioctl(2) system call when 32 bit system calls
are used on 64 bit kernels.
``compat_ioctl``
called by the ioctl(2) system call when 32 bit system calls are
used on 64 bit kernels.
``mmap``: called by the mmap(2) system call
``mmap``
called by the mmap(2) system call
``open``: called by the VFS when an inode should be opened. When the VFS
``open``
called by the VFS when an inode should be opened. When the VFS
opens a file, it creates a new "struct file". It then calls the
open method for the newly allocated file structure. You might
think that the open method really belongs in
"struct inode_operations", and you may be right. I think it's
done the way it is because it makes filesystems simpler to
implement. The open() method is a good place to initialize the
think that the open method really belongs in "struct
inode_operations", and you may be right. I think it's done the
way it is because it makes filesystems simpler to implement.
The open() method is a good place to initialize the
"private_data" member in the file structure if you want to point
to a device structure
``flush``: called by the close(2) system call to flush a file
``flush``
called by the close(2) system call to flush a file
``release``: called when the last reference to an open file is closed
``release``
called when the last reference to an open file is closed
``fsync``: called by the fsync(2) system call. Also see the section above
entitled "Handling errors during writeback".
``fsync``
called by the fsync(2) system call. Also see the section above
entitled "Handling errors during writeback".
``fasync``: called by the fcntl(2) system call when asynchronous
``fasync``
called by the fcntl(2) system call when asynchronous
(non-blocking) mode is enabled for a file
``lock``: called by the fcntl(2) system call for F_GETLK, F_SETLK, and F_SETLKW
commands
``lock``
called by the fcntl(2) system call for F_GETLK, F_SETLK, and
F_SETLKW commands
``get_unmapped_area``: called by the mmap(2) system call
``get_unmapped_area``
called by the mmap(2) system call
``check_flags``: called by the fcntl(2) system call for F_SETFL command
``check_flags``
called by the fcntl(2) system call for F_SETFL command
``flock``: called by the flock(2) system call
``flock``
called by the flock(2) system call
``splice_write``: called by the VFS to splice data from a pipe to a file. This
method is used by the splice(2) system call
``splice_write``
called by the VFS to splice data from a pipe to a file. This
method is used by the splice(2) system call
``splice_read``: called by the VFS to splice data from file to a pipe. This
method is used by the splice(2) system call
``splice_read``
called by the VFS to splice data from file to a pipe. This
method is used by the splice(2) system call
``setlease``: called by the VFS to set or release a file lock lease. setlease
implementations should call generic_setlease to record or remove
the lease in the inode after setting it.
``setlease``
called by the VFS to set or release a file lock lease. setlease
implementations should call generic_setlease to record or remove
the lease in the inode after setting it.
``fallocate``: called by the VFS to preallocate blocks or punch a hole.
``fallocate``
called by the VFS to preallocate blocks or punch a hole.
``copy_file_range``: called by the copy_file_range(2) system call.
``copy_file_range``
called by the copy_file_range(2) system call.
``remap_file_range``: called by the ioctl(2) system call for FICLONERANGE and
FICLONE and FIDEDUPERANGE commands to remap file ranges. An
implementation should remap len bytes at pos_in of the source file into
the dest file at pos_out. Implementations must handle callers passing
in len == 0; this means "remap to the end of the source file". The
return value should the number of bytes remapped, or the usual
negative error code if errors occurred before any bytes were remapped.
The remap_flags parameter accepts REMAP_FILE_* flags. If
REMAP_FILE_DEDUP is set then the implementation must only remap if the
requested file ranges have identical contents. If REMAP_CAN_SHORTEN is
set, the caller is ok with the implementation shortening the request
length to satisfy alignment or EOF requirements (or any other reason).
``remap_file_range``
called by the ioctl(2) system call for FICLONERANGE and FICLONE
and FIDEDUPERANGE commands to remap file ranges. An
implementation should remap len bytes at pos_in of the source
file into the dest file at pos_out. Implementations must handle
callers passing in len == 0; this means "remap to the end of the
source file". The return value should the number of bytes
remapped, or the usual negative error code if errors occurred
before any bytes were remapped. The remap_flags parameter
accepts REMAP_FILE_* flags. If REMAP_FILE_DEDUP is set then the
implementation must only remap if the requested file ranges have
identical contents. If REMAP_CAN_SHORTEN is set, the caller is
ok with the implementation shortening the request length to
satisfy alignment or EOF requirements (or any other reason).
``fadvise``: possibly called by the fadvise64() system call.
``fadvise``
possibly called by the fadvise64() system call.
Note that the file operations are implemented by the specific
filesystem in which the inode resides. When opening a device node
......@@ -1041,89 +1151,104 @@ defined:
struct dentry *(*d_real)(struct dentry *, const struct inode *);
};
``d_revalidate``: called when the VFS needs to revalidate a dentry. This
is called whenever a name look-up finds a dentry in the
dcache. Most local filesystems leave this as NULL, because all their
dentries in the dcache are valid. Network filesystems are different
since things can change on the server without the client necessarily
being aware of it.
This function should return a positive value if the dentry is still
valid, and zero or a negative error code if it isn't.
d_revalidate may be called in rcu-walk mode (flags & LOOKUP_RCU).
If in rcu-walk mode, the filesystem must revalidate the dentry without
blocking or storing to the dentry, d_parent and d_inode should not be
used without care (because they can change and, in d_inode case, even
become NULL under us).
If a situation is encountered that rcu-walk cannot handle, return
``d_revalidate``
called when the VFS needs to revalidate a dentry. This is
called whenever a name look-up finds a dentry in the dcache.
Most local filesystems leave this as NULL, because all their
dentries in the dcache are valid. Network filesystems are
different since things can change on the server without the
client necessarily being aware of it.
This function should return a positive value if the dentry is
still valid, and zero or a negative error code if it isn't.
d_revalidate may be called in rcu-walk mode (flags &
LOOKUP_RCU). If in rcu-walk mode, the filesystem must
revalidate the dentry without blocking or storing to the dentry,
d_parent and d_inode should not be used without care (because
they can change and, in d_inode case, even become NULL under
us).
If a situation is encountered that rcu-walk cannot handle,
return
-ECHILD and it will be called again in ref-walk mode.
``_weak_revalidate``: called when the VFS needs to revalidate a "jumped" dentry.
This is called when a path-walk ends at dentry that was not acquired by
doing a lookup in the parent directory. This includes "/", "." and "..",
as well as procfs-style symlinks and mountpoint traversal.
``_weak_revalidate``
called when the VFS needs to revalidate a "jumped" dentry. This
is called when a path-walk ends at dentry that was not acquired
by doing a lookup in the parent directory. This includes "/",
"." and "..", as well as procfs-style symlinks and mountpoint
traversal.
In this case, we are less concerned with whether the dentry is still
fully correct, but rather that the inode is still valid. As with
d_revalidate, most local filesystems will set this to NULL since their
dcache entries are always valid.
In this case, we are less concerned with whether the dentry is
still fully correct, but rather that the inode is still valid.
As with d_revalidate, most local filesystems will set this to
NULL since their dcache entries are always valid.
This function has the same return code semantics as d_revalidate.
This function has the same return code semantics as
d_revalidate.
d_weak_revalidate is only called after leaving rcu-walk mode.
``d_hash``: called when the VFS adds a dentry to the hash table. The first
``d_hash``
called when the VFS adds a dentry to the hash table. The first
dentry passed to d_hash is the parent directory that the name is
to be hashed into.
Same locking and synchronisation rules as d_compare regarding
what is safe to dereference etc.
``d_compare``: called to compare a dentry name with a given name. The first
``d_compare``
called to compare a dentry name with a given name. The first
dentry is the parent of the dentry to be compared, the second is
the child dentry. len and name string are properties of the dentry
to be compared. qstr is the name to compare it with.
the child dentry. len and name string are properties of the
dentry to be compared. qstr is the name to compare it with.
Must be constant and idempotent, and should not take locks if
possible, and should not or store into the dentry.
Should not dereference pointers outside the dentry without
lots of care (eg. d_parent, d_inode, d_name should not be used).
However, our vfsmount is pinned, and RCU held, so the dentries and
inodes won't disappear, neither will our sb or filesystem module.
->d_sb may be used.
It is a tricky calling convention because it needs to be called under
"rcu-walk", ie. without any locks or references on things.
``d_delete``: called when the last reference to a dentry is dropped and the
dcache is deciding whether or not to cache it. Return 1 to delete
immediately, or 0 to cache the dentry. Default is NULL which means to
always cache a reachable dentry. d_delete must be constant and
idempotent.
``d_init``: called when a dentry is allocated
``d_release``: called when a dentry is really deallocated
``d_iput``: called when a dentry loses its inode (just prior to its
being deallocated). The default when this is NULL is that the
VFS calls iput(). If you define this method, you must call
iput() yourself
``d_dname``: called when the pathname of a dentry should be generated.
Useful for some pseudo filesystems (sockfs, pipefs, ...) to delay
pathname generation. (Instead of doing it when dentry is created,
it's done only when the path is needed.). Real filesystems probably
dont want to use it, because their dentries are present in global
dcache hash, so their hash should be an invariant. As no lock is
held, d_dname() should not try to modify the dentry itself, unless
appropriate SMP safety is used. CAUTION : d_path() logic is quite
tricky. The correct way to return for example "Hello" is to put it
at the end of the buffer, and returns a pointer to the first char.
dynamic_dname() helper function is provided to take care of this.
possible, and should not or store into the dentry. Should not
dereference pointers outside the dentry without lots of care
(eg. d_parent, d_inode, d_name should not be used).
However, our vfsmount is pinned, and RCU held, so the dentries
and inodes won't disappear, neither will our sb or filesystem
module. ->d_sb may be used.
It is a tricky calling convention because it needs to be called
under "rcu-walk", ie. without any locks or references on things.
``d_delete``
called when the last reference to a dentry is dropped and the
dcache is deciding whether or not to cache it. Return 1 to
delete immediately, or 0 to cache the dentry. Default is NULL
which means to always cache a reachable dentry. d_delete must
be constant and idempotent.
``d_init``
called when a dentry is allocated
``d_release``
called when a dentry is really deallocated
``d_iput``
called when a dentry loses its inode (just prior to its being
deallocated). The default when this is NULL is that the VFS
calls iput(). If you define this method, you must call iput()
yourself
``d_dname``
called when the pathname of a dentry should be generated.
Useful for some pseudo filesystems (sockfs, pipefs, ...) to
delay pathname generation. (Instead of doing it when dentry is
created, it's done only when the path is needed.). Real
filesystems probably dont want to use it, because their dentries
are present in global dcache hash, so their hash should be an
invariant. As no lock is held, d_dname() should not try to
modify the dentry itself, unless appropriate SMP safety is used.
CAUTION : d_path() logic is quite tricky. The correct way to
return for example "Hello" is to put it at the end of the
buffer, and returns a pointer to the first char.
dynamic_dname() helper function is provided to take care of
this.
Example :
......@@ -1135,52 +1260,57 @@ defined:
dentry->d_inode->i_ino);
}
``d_automount``: called when an automount dentry is to be traversed (optional).
This should create a new VFS mount record and return the record to the
caller. The caller is supplied with a path parameter giving the
automount directory to describe the automount target and the parent
VFS mount record to provide inheritable mount parameters. NULL should
be returned if someone else managed to make the automount first. If
the vfsmount creation failed, then an error code should be returned.
If -EISDIR is returned, then the directory will be treated as an
ordinary directory and returned to pathwalk to continue walking.
If a vfsmount is returned, the caller will attempt to mount it on the
mountpoint and will remove the vfsmount from its expiration list in
the case of failure. The vfsmount should be returned with 2 refs on
it to prevent automatic expiration - the caller will clean up the
additional ref.
This function is only used if DCACHE_NEED_AUTOMOUNT is set on the
dentry. This is set by __d_instantiate() if S_AUTOMOUNT is set on the
inode being added.
``d_manage``: called to allow the filesystem to manage the transition from a
dentry (optional). This allows autofs, for example, to hold up clients
waiting to explore behind a 'mountpoint' while letting the daemon go
past and construct the subtree there. 0 should be returned to let the
calling process continue. -EISDIR can be returned to tell pathwalk to
use this directory as an ordinary directory and to ignore anything
mounted on it and not to check the automount flag. Any other error
code will abort pathwalk completely.
``d_automount``
called when an automount dentry is to be traversed (optional).
This should create a new VFS mount record and return the record
to the caller. The caller is supplied with a path parameter
giving the automount directory to describe the automount target
and the parent VFS mount record to provide inheritable mount
parameters. NULL should be returned if someone else managed to
make the automount first. If the vfsmount creation failed, then
an error code should be returned. If -EISDIR is returned, then
the directory will be treated as an ordinary directory and
returned to pathwalk to continue walking.
If a vfsmount is returned, the caller will attempt to mount it
on the mountpoint and will remove the vfsmount from its
expiration list in the case of failure. The vfsmount should be
returned with 2 refs on it to prevent automatic expiration - the
caller will clean up the additional ref.
This function is only used if DCACHE_NEED_AUTOMOUNT is set on
the dentry. This is set by __d_instantiate() if S_AUTOMOUNT is
set on the inode being added.
``d_manage``
called to allow the filesystem to manage the transition from a
dentry (optional). This allows autofs, for example, to hold up
clients waiting to explore behind a 'mountpoint' while letting
the daemon go past and construct the subtree there. 0 should be
returned to let the calling process continue. -EISDIR can be
returned to tell pathwalk to use this directory as an ordinary
directory and to ignore anything mounted on it and not to check
the automount flag. Any other error code will abort pathwalk
completely.
If the 'rcu_walk' parameter is true, then the caller is doing a
pathwalk in RCU-walk mode. Sleeping is not permitted in this mode,
and the caller can be asked to leave it and call again by returning
-ECHILD. -EISDIR may also be returned to tell pathwalk to
ignore d_automount or any mounts.
pathwalk in RCU-walk mode. Sleeping is not permitted in this
mode, and the caller can be asked to leave it and call again by
returning -ECHILD. -EISDIR may also be returned to tell
pathwalk to ignore d_automount or any mounts.
This function is only used if DCACHE_MANAGE_TRANSIT is set on the
dentry being transited from.
This function is only used if DCACHE_MANAGE_TRANSIT is set on
the dentry being transited from.
``d_real``: overlay/union type filesystems implement this method to return one of
the underlying dentries hidden by the overlay. It is used in two
different modes:
``d_real``
overlay/union type filesystems implement this method to return
one of the underlying dentries hidden by the overlay. It is
used in two different modes:
Called from file_dentry() it returns the real dentry matching the inode
argument. The real dentry may be from a lower layer already copied up,
but still referenced from the file. This mode is selected with a
non-NULL inode argument.
Called from file_dentry() it returns the real dentry matching
the inode argument. The real dentry may be from a lower layer
already copied up, but still referenced from the file. This
mode is selected with a non-NULL inode argument.
With NULL inode the topmost real underlying dentry is returned.
......@@ -1195,40 +1325,47 @@ Directory Entry Cache API
There are a number of functions defined which permit a filesystem to
manipulate dentries:
``dget``: open a new handle for an existing dentry (this just increments
``dget``
open a new handle for an existing dentry (this just increments
the usage count)
``dput``: close a handle for a dentry (decrements the usage count). If
``dput``
close a handle for a dentry (decrements the usage count). If
the usage count drops to 0, and the dentry is still in its
parent's hash, the "d_delete" method is called to check whether
it should be cached. If it should not be cached, or if the dentry
is not hashed, it is deleted. Otherwise cached dentries are put
into an LRU list to be reclaimed on memory shortage.
``d_drop``: this unhashes a dentry from its parents hash list. A
subsequent call to dput() will deallocate the dentry if its
usage count drops to 0
``d_delete``: delete a dentry. If there are no other open references to
the dentry then the dentry is turned into a negative dentry
(the d_iput() method is called). If there are other
references, then d_drop() is called instead
``d_add``: add a dentry to its parents hash list and then calls
it should be cached. If it should not be cached, or if the
dentry is not hashed, it is deleted. Otherwise cached dentries
are put into an LRU list to be reclaimed on memory shortage.
``d_drop``
this unhashes a dentry from its parents hash list. A subsequent
call to dput() will deallocate the dentry if its usage count
drops to 0
``d_delete``
delete a dentry. If there are no other open references to the
dentry then the dentry is turned into a negative dentry (the
d_iput() method is called). If there are other references, then
d_drop() is called instead
``d_add``
add a dentry to its parents hash list and then calls
d_instantiate()
``d_instantiate``: add a dentry to the alias hash list for the inode and
updates the "d_inode" member. The "i_count" member in the
inode structure should be set/incremented. If the inode
pointer is NULL, the dentry is called a "negative
dentry". This function is commonly called when an inode is
created for an existing negative dentry
``d_lookup``: look up a dentry given its parent and path name component
It looks up the child of that given name from the dcache
hash table. If it is found, the reference count is incremented
and the dentry is returned. The caller must use dput()
to free the dentry when it finishes using it.
``d_instantiate``
add a dentry to the alias hash list for the inode and updates
the "d_inode" member. The "i_count" member in the inode
structure should be set/incremented. If the inode pointer is
NULL, the dentry is called a "negative dentry". This function
is commonly called when an inode is created for an existing
negative dentry
``d_lookup``
look up a dentry given its parent and path name component It
looks up the child of that given name from the dcache hash
table. If it is found, the reference count is incremented and
the dentry is returned. The caller must use dput() to free the
dentry when it finishes using it.
Mount Options
......
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