| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-Id: <20190604002656.30925-1-tobin@kernel.org>
Date: Tue, 4 Jun 2019 10:26:56 +1000
From: "Tobin C. Harding" <tobin@...nel.org>
To: Jonathan Corbet <corbet@....net>
Cc: "Tobin C. Harding" <tobin@...nel.org>,
Al Viro <viro@...iv.linux.org.uk>, Neil Brown <neilb@...e.com>,
Randy Dunlap <rdunlap@...radead.org>,
linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] 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: Jonathan Corbet <corbet@....net>
Signed-off-by: Tobin C. Harding <tobin@...nel.org>
---
Jon,
As discussed on LKML; this patch applies on top of the series
[PATCH v4 0/9] docs: Convert VFS doc to RST
If it does not apply cleanly to your branch please feel free to ask me
to fix it.
thanks,
Tobin.
Documentation/filesystems/vfs.rst | 1146 ++++++++++++++++-------------
1 file changed, 642 insertions(+), 504 deletions(-)
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 3acb74bdddf6..4899085e98d9 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -127,35 +127,46 @@ 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
@@ -180,22 +191,27 @@ 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
@@ -242,87 +258,106 @@ 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
@@ -336,23 +371,31 @@ 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,
@@ -401,121 +444,141 @@ 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).
-``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
@@ -668,70 +731,75 @@ 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.
@@ -739,114 +807,128 @@ 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
@@ -907,91 +989,120 @@ 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
@@ -1036,89 +1147,104 @@ 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 :
@@ -1130,52 +1256,57 @@ 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.
@@ -1190,40 +1321,47 @@ 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
--
2.21.0
Powered by blists - more mailing lists