2005-04-17 06:20:36 +08:00
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The text below describes the locking rules for VFS-related methods.
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It is (believed to be) up-to-date. *Please*, if you change anything in
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prototypes or locking protocols - update this file. And update the relevant
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instances in the tree, don't leave that to maintainers of filesystems/devices/
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etc. At the very least, put the list of dubious cases in the end of this file.
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Don't turn it into log - maintainers of out-of-the-tree code are supposed to
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be able to use diff(1).
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Thing currently missing here: socket operations. Alexey?
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--------------------------- dentry_operations --------------------------
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prototypes:
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2011-01-07 14:49:57 +08:00
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int (*d_revalidate)(struct dentry *, struct nameidata *);
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2011-01-07 14:49:28 +08:00
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int (*d_hash)(const struct dentry *, const struct inode *,
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struct qstr *);
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2011-01-07 14:49:27 +08:00
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int (*d_compare)(const struct dentry *, const struct inode *,
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const struct dentry *, const struct inode *,
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unsigned int, const char *, const struct qstr *);
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2005-04-17 06:20:36 +08:00
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int (*d_delete)(struct dentry *);
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void (*d_release)(struct dentry *);
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void (*d_iput)(struct dentry *, struct inode *);
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2007-05-08 15:26:18 +08:00
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char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
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Add a dentry op to handle automounting rather than abusing follow_link()
Add a dentry op (d_automount) to handle automounting directories rather than
abusing the follow_link() inode operation. The operation is keyed off a new
dentry flag (DCACHE_NEED_AUTOMOUNT).
This also makes it easier to add an AT_ flag to suppress terminal segment
automount during pathwalk and removes the need for the kludge code in the
pathwalk algorithm to handle directories with follow_link() semantics.
The ->d_automount() dentry operation:
struct vfsmount *(*d_automount)(struct path *mountpoint);
takes a pointer to the directory to be mounted upon, which is expected to
provide sufficient data to determine what should be mounted. If successful, it
should return the vfsmount struct it creates (which it should also have added
to the namespace using do_add_mount() or similar). If there's a collision with
another automount attempt, NULL should be returned. If the directory specified
by the parameter should be used directly rather than being mounted upon,
-EISDIR should be returned. In any other case, an error code should be
returned.
The ->d_automount() operation is called with no locks held and may sleep. At
this point the pathwalk algorithm will be in ref-walk mode.
Within fs/namei.c itself, a new pathwalk subroutine (follow_automount()) is
added to handle mountpoints. It will return -EREMOTE if the automount flag was
set, but no d_automount() op was supplied, -ELOOP if we've encountered too many
symlinks or mountpoints, -EISDIR if the walk point should be used without
mounting and 0 if successful. The path will be updated to point to the mounted
filesystem if a successful automount took place.
__follow_mount() is replaced by follow_managed() which is more generic
(especially with the patch that adds ->d_manage()). This handles transits from
directories during pathwalk, including automounting and skipping over
mountpoints (and holding processes with the next patch).
__follow_mount_rcu() will jump out of RCU-walk mode if it encounters an
automount point with nothing mounted on it.
follow_dotdot*() does not handle automounts as you don't want to trigger them
whilst following "..".
I've also extracted the mount/don't-mount logic from autofs4 and included it
here. It makes the mount go ahead anyway if someone calls open() or creat(),
tries to traverse the directory, tries to chdir/chroot/etc. into the directory,
or sticks a '/' on the end of the pathname. If they do a stat(), however,
they'll only trigger the automount if they didn't also say O_NOFOLLOW.
I've also added an inode flag (S_AUTOMOUNT) so that filesystems can mark their
inodes as automount points. This flag is automatically propagated to the
dentry as DCACHE_NEED_AUTOMOUNT by __d_instantiate(). This saves NFS and could
save AFS a private flag bit apiece, but is not strictly necessary. It would be
preferable to do the propagation in d_set_d_op(), but that doesn't normally
have access to the inode.
[AV: fixed breakage in case if __follow_mount_rcu() fails and nameidata_drop_rcu()
succeeds in RCU case of do_lookup(); we need to fall through to non-RCU case after
that, rather than just returning with ungrabbed *path]
Signed-off-by: David Howells <dhowells@redhat.com>
Was-Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-01-15 02:45:21 +08:00
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struct vfsmount *(*d_automount)(struct path *path);
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Add a dentry op to allow processes to be held during pathwalk transit
Add a dentry op (d_manage) to permit a filesystem to hold a process and make it
sleep when it tries to transit away from one of that filesystem's directories
during a pathwalk. The operation is keyed off a new dentry flag
(DCACHE_MANAGE_TRANSIT).
The filesystem is allowed to be selective about which processes it holds and
which it permits to continue on or prohibits from transiting from each flagged
directory. This will allow autofs to hold up client processes whilst letting
its userspace daemon through to maintain the directory or the stuff behind it
or mounted upon it.
The ->d_manage() dentry operation:
int (*d_manage)(struct path *path, bool mounting_here);
takes a pointer to the directory about to be transited away from and a flag
indicating whether the transit is undertaken by do_add_mount() or
do_move_mount() skipping through a pile of filesystems mounted on a mountpoint.
It should return 0 if successful and to let the process continue on its way;
-EISDIR to prohibit the caller from skipping to overmounted filesystems or
automounting, and to use this directory; or some other error code to return to
the user.
->d_manage() is called with namespace_sem writelocked if mounting_here is true
and no other locks held, so it may sleep. However, if mounting_here is true,
it may not initiate or wait for a mount or unmount upon the parameter
directory, even if the act is actually performed by userspace.
Within fs/namei.c, follow_managed() is extended to check with d_manage() first
on each managed directory, before transiting away from it or attempting to
automount upon it.
follow_down() is renamed follow_down_one() and should only be used where the
filesystem deliberately intends to avoid management steps (e.g. autofs).
A new follow_down() is added that incorporates the loop done by all other
callers of follow_down() (do_add/move_mount(), autofs and NFSD; whilst AFS, NFS
and CIFS do use it, their use is removed by converting them to use
d_automount()). The new follow_down() calls d_manage() as appropriate. It
also takes an extra parameter to indicate if it is being called from mount code
(with namespace_sem writelocked) which it passes to d_manage(). follow_down()
ignores automount points so that it can be used to mount on them.
__follow_mount_rcu() is made to abort rcu-walk mode if it hits a directory with
DCACHE_MANAGE_TRANSIT set on the basis that we're probably going to have to
sleep. It would be possible to enter d_manage() in rcu-walk mode too, and have
that determine whether to abort or not itself. That would allow the autofs
daemon to continue on in rcu-walk mode.
Note that DCACHE_MANAGE_TRANSIT on a directory should be cleared when it isn't
required as every tranist from that directory will cause d_manage() to be
invoked. It can always be set again when necessary.
==========================
WHAT THIS MEANS FOR AUTOFS
==========================
Autofs currently uses the lookup() inode op and the d_revalidate() dentry op to
trigger the automounting of indirect mounts, and both of these can be called
with i_mutex held.
autofs knows that the i_mutex will be held by the caller in lookup(), and so
can drop it before invoking the daemon - but this isn't so for d_revalidate(),
since the lock is only held on _some_ of the code paths that call it. This
means that autofs can't risk dropping i_mutex from its d_revalidate() function
before it calls the daemon.
The bug could manifest itself as, for example, a process that's trying to
validate an automount dentry that gets made to wait because that dentry is
expired and needs cleaning up:
mkdir S ffffffff8014e05a 0 32580 24956
Call Trace:
[<ffffffff885371fd>] :autofs4:autofs4_wait+0x674/0x897
[<ffffffff80127f7d>] avc_has_perm+0x46/0x58
[<ffffffff8009fdcf>] autoremove_wake_function+0x0/0x2e
[<ffffffff88537be6>] :autofs4:autofs4_expire_wait+0x41/0x6b
[<ffffffff88535cfc>] :autofs4:autofs4_revalidate+0x91/0x149
[<ffffffff80036d96>] __lookup_hash+0xa0/0x12f
[<ffffffff80057a2f>] lookup_create+0x46/0x80
[<ffffffff800e6e31>] sys_mkdirat+0x56/0xe4
versus the automount daemon which wants to remove that dentry, but can't
because the normal process is holding the i_mutex lock:
automount D ffffffff8014e05a 0 32581 1 32561
Call Trace:
[<ffffffff80063c3f>] __mutex_lock_slowpath+0x60/0x9b
[<ffffffff8000ccf1>] do_path_lookup+0x2ca/0x2f1
[<ffffffff80063c89>] .text.lock.mutex+0xf/0x14
[<ffffffff800e6d55>] do_rmdir+0x77/0xde
[<ffffffff8005d229>] tracesys+0x71/0xe0
[<ffffffff8005d28d>] tracesys+0xd5/0xe0
which means that the system is deadlocked.
This patch allows autofs to hold up normal processes whilst the daemon goes
ahead and does things to the dentry tree behind the automouter point without
risking a deadlock as almost no locks are held in d_manage() and none in
d_automount().
Signed-off-by: David Howells <dhowells@redhat.com>
Was-Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-01-15 02:45:26 +08:00
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int (*d_manage)(struct dentry *, bool);
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2005-04-17 06:20:36 +08:00
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locking rules:
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2011-01-07 14:49:57 +08:00
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rename_lock ->d_lock may block rcu-walk
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d_revalidate: no no yes (ref-walk) maybe
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d_hash no no no maybe
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d_compare: yes no no maybe
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d_delete: no yes no no
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d_release: no no yes no
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d_iput: no no yes no
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d_dname: no no no no
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Add a dentry op to handle automounting rather than abusing follow_link()
Add a dentry op (d_automount) to handle automounting directories rather than
abusing the follow_link() inode operation. The operation is keyed off a new
dentry flag (DCACHE_NEED_AUTOMOUNT).
This also makes it easier to add an AT_ flag to suppress terminal segment
automount during pathwalk and removes the need for the kludge code in the
pathwalk algorithm to handle directories with follow_link() semantics.
The ->d_automount() dentry operation:
struct vfsmount *(*d_automount)(struct path *mountpoint);
takes a pointer to the directory to be mounted upon, which is expected to
provide sufficient data to determine what should be mounted. If successful, it
should return the vfsmount struct it creates (which it should also have added
to the namespace using do_add_mount() or similar). If there's a collision with
another automount attempt, NULL should be returned. If the directory specified
by the parameter should be used directly rather than being mounted upon,
-EISDIR should be returned. In any other case, an error code should be
returned.
The ->d_automount() operation is called with no locks held and may sleep. At
this point the pathwalk algorithm will be in ref-walk mode.
Within fs/namei.c itself, a new pathwalk subroutine (follow_automount()) is
added to handle mountpoints. It will return -EREMOTE if the automount flag was
set, but no d_automount() op was supplied, -ELOOP if we've encountered too many
symlinks or mountpoints, -EISDIR if the walk point should be used without
mounting and 0 if successful. The path will be updated to point to the mounted
filesystem if a successful automount took place.
__follow_mount() is replaced by follow_managed() which is more generic
(especially with the patch that adds ->d_manage()). This handles transits from
directories during pathwalk, including automounting and skipping over
mountpoints (and holding processes with the next patch).
__follow_mount_rcu() will jump out of RCU-walk mode if it encounters an
automount point with nothing mounted on it.
follow_dotdot*() does not handle automounts as you don't want to trigger them
whilst following "..".
I've also extracted the mount/don't-mount logic from autofs4 and included it
here. It makes the mount go ahead anyway if someone calls open() or creat(),
tries to traverse the directory, tries to chdir/chroot/etc. into the directory,
or sticks a '/' on the end of the pathname. If they do a stat(), however,
they'll only trigger the automount if they didn't also say O_NOFOLLOW.
I've also added an inode flag (S_AUTOMOUNT) so that filesystems can mark their
inodes as automount points. This flag is automatically propagated to the
dentry as DCACHE_NEED_AUTOMOUNT by __d_instantiate(). This saves NFS and could
save AFS a private flag bit apiece, but is not strictly necessary. It would be
preferable to do the propagation in d_set_d_op(), but that doesn't normally
have access to the inode.
[AV: fixed breakage in case if __follow_mount_rcu() fails and nameidata_drop_rcu()
succeeds in RCU case of do_lookup(); we need to fall through to non-RCU case after
that, rather than just returning with ungrabbed *path]
Signed-off-by: David Howells <dhowells@redhat.com>
Was-Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-01-15 02:45:21 +08:00
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d_automount: no no yes no
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2011-01-15 02:46:51 +08:00
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d_manage: no no yes (ref-walk) maybe
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2005-04-17 06:20:36 +08:00
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--------------------------- inode_operations ---------------------------
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prototypes:
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int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
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struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameid
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ata *);
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int (*link) (struct dentry *,struct inode *,struct dentry *);
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int (*unlink) (struct inode *,struct dentry *);
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int (*symlink) (struct inode *,struct dentry *,const char *);
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int (*mkdir) (struct inode *,struct dentry *,int);
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int (*rmdir) (struct inode *,struct dentry *);
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int (*mknod) (struct inode *,struct dentry *,int,dev_t);
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int (*rename) (struct inode *, struct dentry *,
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struct inode *, struct dentry *);
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int (*readlink) (struct dentry *, char __user *,int);
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2010-12-16 19:04:54 +08:00
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void * (*follow_link) (struct dentry *, struct nameidata *);
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void (*put_link) (struct dentry *, struct nameidata *, void *);
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2005-04-17 06:20:36 +08:00
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void (*truncate) (struct inode *);
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2011-01-07 14:49:58 +08:00
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int (*permission) (struct inode *, int, unsigned int);
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int (*check_acl)(struct inode *, int, unsigned int);
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2005-04-17 06:20:36 +08:00
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int (*setattr) (struct dentry *, struct iattr *);
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int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
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int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
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ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
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ssize_t (*listxattr) (struct dentry *, char *, size_t);
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int (*removexattr) (struct dentry *, const char *);
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2010-12-16 19:04:54 +08:00
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void (*truncate_range)(struct inode *, loff_t, loff_t);
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int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
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2005-04-17 06:20:36 +08:00
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locking rules:
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2010-12-16 19:04:54 +08:00
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all may block
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2007-05-09 13:53:16 +08:00
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i_mutex(inode)
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2005-04-17 06:20:36 +08:00
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lookup: yes
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create: yes
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link: yes (both)
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mknod: yes
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symlink: yes
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mkdir: yes
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unlink: yes (both)
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rmdir: yes (both) (see below)
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rename: yes (all) (see below)
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readlink: no
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follow_link: no
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2010-12-16 19:04:54 +08:00
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put_link: no
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2005-04-17 06:20:36 +08:00
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truncate: yes (see below)
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setattr: yes
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2011-01-07 14:49:58 +08:00
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permission: no (may not block if called in rcu-walk mode)
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2010-12-16 19:04:54 +08:00
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check_acl: no
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2005-04-17 06:20:36 +08:00
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getattr: no
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setxattr: yes
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getxattr: no
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listxattr: no
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removexattr: yes
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2010-12-16 19:04:54 +08:00
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truncate_range: yes
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fiemap: no
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2007-05-09 13:53:16 +08:00
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Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
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2005-04-17 06:20:36 +08:00
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victim.
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cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
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->truncate() is never called directly - it's a callback, not a
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2010-12-16 19:04:54 +08:00
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method. It's called by vmtruncate() - deprecated library function used by
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2005-04-17 06:20:36 +08:00
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->setattr(). Locking information above applies to that call (i.e. is
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inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been
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passed).
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See Documentation/filesystems/directory-locking for more detailed discussion
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of the locking scheme for directory operations.
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--------------------------- super_operations ---------------------------
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prototypes:
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struct inode *(*alloc_inode)(struct super_block *sb);
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void (*destroy_inode)(struct inode *);
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void (*dirty_inode) (struct inode *);
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2010-12-16 19:04:54 +08:00
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int (*write_inode) (struct inode *, struct writeback_control *wbc);
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2010-06-08 12:37:12 +08:00
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int (*drop_inode) (struct inode *);
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void (*evict_inode) (struct inode *);
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2005-04-17 06:20:36 +08:00
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void (*put_super) (struct super_block *);
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void (*write_super) (struct super_block *);
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int (*sync_fs)(struct super_block *sb, int wait);
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2009-01-10 08:40:58 +08:00
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int (*freeze_fs) (struct super_block *);
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int (*unfreeze_fs) (struct super_block *);
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2006-06-23 17:02:58 +08:00
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int (*statfs) (struct dentry *, struct kstatfs *);
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2005-04-17 06:20:36 +08:00
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int (*remount_fs) (struct super_block *, int *, char *);
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void (*umount_begin) (struct super_block *);
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int (*show_options)(struct seq_file *, struct vfsmount *);
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ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
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ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
|
2010-12-16 19:04:54 +08:00
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int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
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2005-04-17 06:20:36 +08:00
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locking rules:
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2010-06-08 12:37:12 +08:00
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All may block [not true, see below]
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2009-06-20 02:22:37 +08:00
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s_umount
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alloc_inode:
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destroy_inode:
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dirty_inode: (must not sleep)
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write_inode:
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drop_inode: !!!inode_lock!!!
|
2010-06-08 12:37:12 +08:00
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evict_inode:
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2009-06-20 02:22:37 +08:00
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put_super: write
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write_super: read
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sync_fs: read
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freeze_fs: read
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unfreeze_fs: read
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2010-06-08 12:37:12 +08:00
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statfs: maybe(read) (see below)
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remount_fs: write
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2009-06-20 02:22:37 +08:00
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umount_begin: no
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show_options: no (namespace_sem)
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quota_read: no (see below)
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quota_write: no (see below)
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2010-12-16 19:04:54 +08:00
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bdev_try_to_free_page: no (see below)
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2005-04-17 06:20:36 +08:00
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2010-06-08 12:37:12 +08:00
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->statfs() has s_umount (shared) when called by ustat(2) (native or
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compat), but that's an accident of bad API; s_umount is used to pin
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the superblock down when we only have dev_t given us by userland to
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|
|
|
|
identify the superblock. Everything else (statfs(), fstatfs(), etc.)
|
|
|
|
|
doesn't hold it when calling ->statfs() - superblock is pinned down
|
|
|
|
|
by resolving the pathname passed to syscall.
|
2005-04-17 06:20:36 +08:00
|
|
|
->quota_read() and ->quota_write() functions are both guaranteed to
|
|
|
|
|
be the only ones operating on the quota file by the quota code (via
|
|
|
|
|
dqio_sem) (unless an admin really wants to screw up something and
|
|
|
|
|
writes to quota files with quotas on). For other details about locking
|
|
|
|
|
see also dquot_operations section.
|
2010-12-16 19:04:54 +08:00
|
|
|
->bdev_try_to_free_page is called from the ->releasepage handler of
|
|
|
|
|
the block device inode. See there for more details.
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
--------------------------- file_system_type ---------------------------
|
|
|
|
|
prototypes:
|
2006-07-10 19:44:07 +08:00
|
|
|
int (*get_sb) (struct file_system_type *, int,
|
|
|
|
|
const char *, void *, struct vfsmount *);
|
2010-12-16 19:04:54 +08:00
|
|
|
struct dentry *(*mount) (struct file_system_type *, int,
|
|
|
|
|
const char *, void *);
|
2005-04-17 06:20:36 +08:00
|
|
|
void (*kill_sb) (struct super_block *);
|
|
|
|
|
locking rules:
|
2010-12-16 19:04:54 +08:00
|
|
|
may block
|
|
|
|
|
mount yes
|
|
|
|
|
kill_sb yes
|
2005-04-17 06:20:36 +08:00
|
|
|
|
2011-03-16 21:07:58 +08:00
|
|
|
->mount() returns ERR_PTR or the root dentry; its superblock should be locked
|
|
|
|
|
on return.
|
2005-04-17 06:20:36 +08:00
|
|
|
->kill_sb() takes a write-locked superblock, does all shutdown work on it,
|
|
|
|
|
unlocks and drops the reference.
|
|
|
|
|
|
|
|
|
|
--------------------------- address_space_operations --------------------------
|
|
|
|
|
prototypes:
|
|
|
|
|
int (*writepage)(struct page *page, struct writeback_control *wbc);
|
|
|
|
|
int (*readpage)(struct file *, struct page *);
|
|
|
|
|
int (*sync_page)(struct page *);
|
|
|
|
|
int (*writepages)(struct address_space *, struct writeback_control *);
|
|
|
|
|
int (*set_page_dirty)(struct page *page);
|
|
|
|
|
int (*readpages)(struct file *filp, struct address_space *mapping,
|
|
|
|
|
struct list_head *pages, unsigned nr_pages);
|
2008-10-30 05:00:55 +08:00
|
|
|
int (*write_begin)(struct file *, struct address_space *mapping,
|
|
|
|
|
loff_t pos, unsigned len, unsigned flags,
|
|
|
|
|
struct page **pagep, void **fsdata);
|
|
|
|
|
int (*write_end)(struct file *, struct address_space *mapping,
|
|
|
|
|
loff_t pos, unsigned len, unsigned copied,
|
|
|
|
|
struct page *page, void *fsdata);
|
2005-04-17 06:20:36 +08:00
|
|
|
sector_t (*bmap)(struct address_space *, sector_t);
|
|
|
|
|
int (*invalidatepage) (struct page *, unsigned long);
|
|
|
|
|
int (*releasepage) (struct page *, int);
|
2010-12-02 02:35:19 +08:00
|
|
|
void (*freepage)(struct page *);
|
2005-04-17 06:20:36 +08:00
|
|
|
int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
|
|
|
|
|
loff_t offset, unsigned long nr_segs);
|
2010-12-16 19:04:54 +08:00
|
|
|
int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **,
|
|
|
|
|
unsigned long *);
|
|
|
|
|
int (*migratepage)(struct address_space *, struct page *, struct page *);
|
|
|
|
|
int (*launder_page)(struct page *);
|
|
|
|
|
int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
|
|
|
|
|
int (*error_remove_page)(struct address_space *, struct page *);
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
locking rules:
|
2010-12-02 02:35:19 +08:00
|
|
|
All except set_page_dirty and freepage may block
|
2005-04-17 06:20:36 +08:00
|
|
|
|
2010-12-16 19:04:54 +08:00
|
|
|
PageLocked(page) i_mutex
|
|
|
|
|
writepage: yes, unlocks (see below)
|
|
|
|
|
readpage: yes, unlocks
|
|
|
|
|
sync_page: maybe
|
|
|
|
|
writepages:
|
|
|
|
|
set_page_dirty no
|
|
|
|
|
readpages:
|
|
|
|
|
write_begin: locks the page yes
|
|
|
|
|
write_end: yes, unlocks yes
|
|
|
|
|
bmap:
|
|
|
|
|
invalidatepage: yes
|
|
|
|
|
releasepage: yes
|
|
|
|
|
freepage: yes
|
|
|
|
|
direct_IO:
|
|
|
|
|
get_xip_mem: maybe
|
|
|
|
|
migratepage: yes (both)
|
|
|
|
|
launder_page: yes
|
|
|
|
|
is_partially_uptodate: yes
|
|
|
|
|
error_remove_page: yes
|
2005-04-17 06:20:36 +08:00
|
|
|
|
2008-10-30 05:00:55 +08:00
|
|
|
->write_begin(), ->write_end(), ->sync_page() and ->readpage()
|
2005-04-17 06:20:36 +08:00
|
|
|
may be called from the request handler (/dev/loop).
|
|
|
|
|
|
|
|
|
|
->readpage() unlocks the page, either synchronously or via I/O
|
|
|
|
|
completion.
|
|
|
|
|
|
|
|
|
|
->readpages() populates the pagecache with the passed pages and starts
|
|
|
|
|
I/O against them. They come unlocked upon I/O completion.
|
|
|
|
|
|
|
|
|
|
->writepage() is used for two purposes: for "memory cleansing" and for
|
|
|
|
|
"sync". These are quite different operations and the behaviour may differ
|
|
|
|
|
depending upon the mode.
|
|
|
|
|
|
|
|
|
|
If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
|
|
|
|
|
it *must* start I/O against the page, even if that would involve
|
|
|
|
|
blocking on in-progress I/O.
|
|
|
|
|
|
|
|
|
|
If writepage is called for memory cleansing (sync_mode ==
|
|
|
|
|
WBC_SYNC_NONE) then its role is to get as much writeout underway as
|
|
|
|
|
possible. So writepage should try to avoid blocking against
|
|
|
|
|
currently-in-progress I/O.
|
|
|
|
|
|
|
|
|
|
If the filesystem is not called for "sync" and it determines that it
|
|
|
|
|
would need to block against in-progress I/O to be able to start new I/O
|
|
|
|
|
against the page the filesystem should redirty the page with
|
|
|
|
|
redirty_page_for_writepage(), then unlock the page and return zero.
|
|
|
|
|
This may also be done to avoid internal deadlocks, but rarely.
|
|
|
|
|
|
2007-10-20 05:10:43 +08:00
|
|
|
If the filesystem is called for sync then it must wait on any
|
2005-04-17 06:20:36 +08:00
|
|
|
in-progress I/O and then start new I/O.
|
|
|
|
|
|
2005-05-01 23:58:37 +08:00
|
|
|
The filesystem should unlock the page synchronously, before returning to the
|
|
|
|
|
caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
|
|
|
|
|
value. WRITEPAGE_ACTIVATE means that page cannot really be written out
|
|
|
|
|
currently, and VM should stop calling ->writepage() on this page for some
|
|
|
|
|
time. VM does this by moving page to the head of the active list, hence the
|
|
|
|
|
name.
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
|
|
|
|
|
and return zero, writepage *must* run set_page_writeback() against the page,
|
|
|
|
|
followed by unlocking it. Once set_page_writeback() has been run against the
|
|
|
|
|
page, write I/O can be submitted and the write I/O completion handler must run
|
|
|
|
|
end_page_writeback() once the I/O is complete. If no I/O is submitted, the
|
|
|
|
|
filesystem must run end_page_writeback() against the page before returning from
|
|
|
|
|
writepage.
|
|
|
|
|
|
|
|
|
|
That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
|
|
|
|
|
if the filesystem needs the page to be locked during writeout, that is ok, too,
|
|
|
|
|
the page is allowed to be unlocked at any point in time between the calls to
|
|
|
|
|
set_page_writeback() and end_page_writeback().
|
|
|
|
|
|
|
|
|
|
Note, failure to run either redirty_page_for_writepage() or the combination of
|
|
|
|
|
set_page_writeback()/end_page_writeback() on a page submitted to writepage
|
|
|
|
|
will leave the page itself marked clean but it will be tagged as dirty in the
|
|
|
|
|
radix tree. This incoherency can lead to all sorts of hard-to-debug problems
|
|
|
|
|
in the filesystem like having dirty inodes at umount and losing written data.
|
|
|
|
|
|
|
|
|
|
->sync_page() locking rules are not well-defined - usually it is called
|
|
|
|
|
with lock on page, but that is not guaranteed. Considering the currently
|
|
|
|
|
existing instances of this method ->sync_page() itself doesn't look
|
|
|
|
|
well-defined...
|
|
|
|
|
|
|
|
|
|
->writepages() is used for periodic writeback and for syscall-initiated
|
|
|
|
|
sync operations. The address_space should start I/O against at least
|
|
|
|
|
*nr_to_write pages. *nr_to_write must be decremented for each page which is
|
|
|
|
|
written. The address_space implementation may write more (or less) pages
|
|
|
|
|
than *nr_to_write asks for, but it should try to be reasonably close. If
|
|
|
|
|
nr_to_write is NULL, all dirty pages must be written.
|
|
|
|
|
|
|
|
|
|
writepages should _only_ write pages which are present on
|
|
|
|
|
mapping->io_pages.
|
|
|
|
|
|
|
|
|
|
->set_page_dirty() is called from various places in the kernel
|
|
|
|
|
when the target page is marked as needing writeback. It may be called
|
|
|
|
|
under spinlock (it cannot block) and is sometimes called with the page
|
|
|
|
|
not locked.
|
|
|
|
|
|
|
|
|
|
->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
|
2010-12-16 19:04:54 +08:00
|
|
|
filesystems and by the swapper. The latter will eventually go away. Please,
|
|
|
|
|
keep it that way and don't breed new callers.
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
->invalidatepage() is called when the filesystem must attempt to drop
|
|
|
|
|
some or all of the buffers from the page when it is being truncated. It
|
|
|
|
|
returns zero on success. If ->invalidatepage is zero, the kernel uses
|
|
|
|
|
block_invalidatepage() instead.
|
|
|
|
|
|
|
|
|
|
->releasepage() is called when the kernel is about to try to drop the
|
|
|
|
|
buffers from the page in preparation for freeing it. It returns zero to
|
|
|
|
|
indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
|
|
|
|
|
the kernel assumes that the fs has no private interest in the buffers.
|
|
|
|
|
|
2010-12-02 02:35:19 +08:00
|
|
|
->freepage() is called when the kernel is done dropping the page
|
|
|
|
|
from the page cache.
|
|
|
|
|
|
2007-01-11 15:15:39 +08:00
|
|
|
->launder_page() may be called prior to releasing a page if
|
|
|
|
|
it is still found to be dirty. It returns zero if the page was successfully
|
|
|
|
|
cleaned, or an error value if not. Note that in order to prevent the page
|
|
|
|
|
getting mapped back in and redirtied, it needs to be kept locked
|
|
|
|
|
across the entire operation.
|
|
|
|
|
|
2005-04-17 06:20:36 +08:00
|
|
|
----------------------- file_lock_operations ------------------------------
|
|
|
|
|
prototypes:
|
|
|
|
|
void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
|
|
|
|
|
void (*fl_release_private)(struct file_lock *);
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
locking rules:
|
2010-12-16 19:04:54 +08:00
|
|
|
file_lock_lock may block
|
|
|
|
|
fl_copy_lock: yes no
|
|
|
|
|
fl_release_private: maybe no
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
----------------------- lock_manager_operations ---------------------------
|
|
|
|
|
prototypes:
|
|
|
|
|
int (*fl_compare_owner)(struct file_lock *, struct file_lock *);
|
|
|
|
|
void (*fl_notify)(struct file_lock *); /* unblock callback */
|
2010-12-16 19:04:54 +08:00
|
|
|
int (*fl_grant)(struct file_lock *, struct file_lock *, int);
|
2005-04-17 06:20:36 +08:00
|
|
|
void (*fl_release_private)(struct file_lock *);
|
|
|
|
|
void (*fl_break)(struct file_lock *); /* break_lease callback */
|
2010-12-16 19:04:54 +08:00
|
|
|
int (*fl_change)(struct file_lock **, int);
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
locking rules:
|
2010-12-16 19:04:54 +08:00
|
|
|
file_lock_lock may block
|
|
|
|
|
fl_compare_owner: yes no
|
|
|
|
|
fl_notify: yes no
|
|
|
|
|
fl_grant: no no
|
|
|
|
|
fl_release_private: maybe no
|
|
|
|
|
fl_break: yes no
|
|
|
|
|
fl_change yes no
|
|
|
|
|
|
2005-04-17 06:20:36 +08:00
|
|
|
--------------------------- buffer_head -----------------------------------
|
|
|
|
|
prototypes:
|
|
|
|
|
void (*b_end_io)(struct buffer_head *bh, int uptodate);
|
|
|
|
|
|
|
|
|
|
locking rules:
|
|
|
|
|
called from interrupts. In other words, extreme care is needed here.
|
|
|
|
|
bh is locked, but that's all warranties we have here. Currently only RAID1,
|
|
|
|
|
highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
|
|
|
|
|
call this method upon the IO completion.
|
|
|
|
|
|
|
|
|
|
--------------------------- block_device_operations -----------------------
|
|
|
|
|
prototypes:
|
2010-10-06 16:46:53 +08:00
|
|
|
int (*open) (struct block_device *, fmode_t);
|
|
|
|
|
int (*release) (struct gendisk *, fmode_t);
|
|
|
|
|
int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
|
|
|
|
|
int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
|
|
|
|
|
int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *);
|
2005-04-17 06:20:36 +08:00
|
|
|
int (*media_changed) (struct gendisk *);
|
2010-10-06 16:46:53 +08:00
|
|
|
void (*unlock_native_capacity) (struct gendisk *);
|
2005-04-17 06:20:36 +08:00
|
|
|
int (*revalidate_disk) (struct gendisk *);
|
2010-10-06 16:46:53 +08:00
|
|
|
int (*getgeo)(struct block_device *, struct hd_geometry *);
|
|
|
|
|
void (*swap_slot_free_notify) (struct block_device *, unsigned long);
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
locking rules:
|
2010-12-16 19:04:54 +08:00
|
|
|
bd_mutex
|
|
|
|
|
open: yes
|
|
|
|
|
release: yes
|
|
|
|
|
ioctl: no
|
|
|
|
|
compat_ioctl: no
|
|
|
|
|
direct_access: no
|
|
|
|
|
media_changed: no
|
|
|
|
|
unlock_native_capacity: no
|
|
|
|
|
revalidate_disk: no
|
|
|
|
|
getgeo: no
|
|
|
|
|
swap_slot_free_notify: no (see below)
|
2010-10-06 16:46:53 +08:00
|
|
|
|
|
|
|
|
media_changed, unlock_native_capacity and revalidate_disk are called only from
|
|
|
|
|
check_disk_change().
|
|
|
|
|
|
|
|
|
|
swap_slot_free_notify is called with swap_lock and sometimes the page lock
|
|
|
|
|
held.
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
|
|
|
|
|
--------------------------- file_operations -------------------------------
|
|
|
|
|
prototypes:
|
|
|
|
|
loff_t (*llseek) (struct file *, loff_t, int);
|
|
|
|
|
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
|
|
|
|
|
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
|
2006-10-01 14:28:46 +08:00
|
|
|
ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
|
|
|
|
|
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
|
2005-04-17 06:20:36 +08:00
|
|
|
int (*readdir) (struct file *, void *, filldir_t);
|
|
|
|
|
unsigned int (*poll) (struct file *, struct poll_table_struct *);
|
|
|
|
|
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
|
|
|
|
|
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
|
|
|
|
|
int (*mmap) (struct file *, struct vm_area_struct *);
|
|
|
|
|
int (*open) (struct inode *, struct file *);
|
|
|
|
|
int (*flush) (struct file *);
|
|
|
|
|
int (*release) (struct inode *, struct file *);
|
2010-05-26 23:53:25 +08:00
|
|
|
int (*fsync) (struct file *, int datasync);
|
2005-04-17 06:20:36 +08:00
|
|
|
int (*aio_fsync) (struct kiocb *, int datasync);
|
|
|
|
|
int (*fasync) (int, struct file *, int);
|
|
|
|
|
int (*lock) (struct file *, int, struct file_lock *);
|
|
|
|
|
ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
|
|
|
|
|
loff_t *);
|
|
|
|
|
ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
|
|
|
|
|
loff_t *);
|
|
|
|
|
ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
|
|
|
|
|
void __user *);
|
|
|
|
|
ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
|
|
|
|
|
loff_t *, int);
|
|
|
|
|
unsigned long (*get_unmapped_area)(struct file *, unsigned long,
|
|
|
|
|
unsigned long, unsigned long, unsigned long);
|
|
|
|
|
int (*check_flags)(int);
|
2010-12-16 19:04:54 +08:00
|
|
|
int (*flock) (struct file *, int, struct file_lock *);
|
|
|
|
|
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
|
|
|
|
|
size_t, unsigned int);
|
|
|
|
|
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
|
|
|
|
|
size_t, unsigned int);
|
|
|
|
|
int (*setlease)(struct file *, long, struct file_lock **);
|
2011-01-14 20:07:43 +08:00
|
|
|
long (*fallocate)(struct file *, int, loff_t, loff_t);
|
2005-04-17 06:20:36 +08:00
|
|
|
};
|
|
|
|
|
|
|
|
|
|
locking rules:
|
2010-12-16 19:04:54 +08:00
|
|
|
All may block except for ->setlease.
|
|
|
|
|
No VFS locks held on entry except for ->fsync and ->setlease.
|
|
|
|
|
|
|
|
|
|
->fsync() has i_mutex on inode.
|
|
|
|
|
|
|
|
|
|
->setlease has the file_list_lock held and must not sleep.
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
->llseek() locking has moved from llseek to the individual llseek
|
|
|
|
|
implementations. If your fs is not using generic_file_llseek, you
|
|
|
|
|
need to acquire and release the appropriate locks in your ->llseek().
|
|
|
|
|
For many filesystems, it is probably safe to acquire the inode
|
2010-05-27 05:44:54 +08:00
|
|
|
mutex or just to use i_size_read() instead.
|
|
|
|
|
Note: this does not protect the file->f_pos against concurrent modifications
|
|
|
|
|
since this is something the userspace has to take care about.
|
2005-04-17 06:20:36 +08:00
|
|
|
|
2010-12-16 19:04:54 +08:00
|
|
|
->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
|
|
|
|
|
Most instances call fasync_helper(), which does that maintenance, so it's
|
|
|
|
|
not normally something one needs to worry about. Return values > 0 will be
|
|
|
|
|
mapped to zero in the VFS layer.
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
->readdir() and ->ioctl() on directories must be changed. Ideally we would
|
|
|
|
|
move ->readdir() to inode_operations and use a separate method for directory
|
|
|
|
|
->ioctl() or kill the latter completely. One of the problems is that for
|
|
|
|
|
anything that resembles union-mount we won't have a struct file for all
|
|
|
|
|
components. And there are other reasons why the current interface is a mess...
|
|
|
|
|
|
|
|
|
|
->read on directories probably must go away - we should just enforce -EISDIR
|
|
|
|
|
in sys_read() and friends.
|
|
|
|
|
|
|
|
|
|
--------------------------- dquot_operations -------------------------------
|
|
|
|
|
prototypes:
|
|
|
|
|
int (*write_dquot) (struct dquot *);
|
|
|
|
|
int (*acquire_dquot) (struct dquot *);
|
|
|
|
|
int (*release_dquot) (struct dquot *);
|
|
|
|
|
int (*mark_dirty) (struct dquot *);
|
|
|
|
|
int (*write_info) (struct super_block *, int);
|
|
|
|
|
|
|
|
|
|
These operations are intended to be more or less wrapping functions that ensure
|
|
|
|
|
a proper locking wrt the filesystem and call the generic quota operations.
|
|
|
|
|
|
|
|
|
|
What filesystem should expect from the generic quota functions:
|
|
|
|
|
|
|
|
|
|
FS recursion Held locks when called
|
|
|
|
|
write_dquot: yes dqonoff_sem or dqptr_sem
|
|
|
|
|
acquire_dquot: yes dqonoff_sem or dqptr_sem
|
|
|
|
|
release_dquot: yes dqonoff_sem or dqptr_sem
|
|
|
|
|
mark_dirty: no -
|
|
|
|
|
write_info: yes dqonoff_sem
|
|
|
|
|
|
|
|
|
|
FS recursion means calling ->quota_read() and ->quota_write() from superblock
|
|
|
|
|
operations.
|
|
|
|
|
|
|
|
|
|
More details about quota locking can be found in fs/dquot.c.
|
|
|
|
|
|
|
|
|
|
--------------------------- vm_operations_struct -----------------------------
|
|
|
|
|
prototypes:
|
|
|
|
|
void (*open)(struct vm_area_struct*);
|
|
|
|
|
void (*close)(struct vm_area_struct*);
|
2007-07-19 16:47:03 +08:00
|
|
|
int (*fault)(struct vm_area_struct*, struct vm_fault *);
|
2009-04-01 06:23:21 +08:00
|
|
|
int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
|
2008-07-24 12:27:05 +08:00
|
|
|
int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
|
2005-04-17 06:20:36 +08:00
|
|
|
|
|
|
|
|
locking rules:
|
2010-12-16 19:04:54 +08:00
|
|
|
mmap_sem PageLocked(page)
|
|
|
|
|
open: yes
|
|
|
|
|
close: yes
|
|
|
|
|
fault: yes can return with page locked
|
|
|
|
|
page_mkwrite: yes can return with page locked
|
|
|
|
|
access: yes
|
2007-07-19 16:47:01 +08:00
|
|
|
|
mm: close page_mkwrite races
Change page_mkwrite to allow implementations to return with the page
locked, and also change it's callers (in page fault paths) to hold the
lock until the page is marked dirty. This allows the filesystem to have
full control of page dirtying events coming from the VM.
Rather than simply hold the page locked over the page_mkwrite call, we
call page_mkwrite with the page unlocked and allow callers to return with
it locked, so filesystems can avoid LOR conditions with page lock.
The problem with the current scheme is this: a filesystem that wants to
associate some metadata with a page as long as the page is dirty, will
perform this manipulation in its ->page_mkwrite. It currently then must
return with the page unlocked and may not hold any other locks (according
to existing page_mkwrite convention).
In this window, the VM could write out the page, clearing page-dirty. The
filesystem has no good way to detect that a dirty pte is about to be
attached, so it will happily write out the page, at which point, the
filesystem may manipulate the metadata to reflect that the page is no
longer dirty.
It is not always possible to perform the required metadata manipulation in
->set_page_dirty, because that function cannot block or fail. The
filesystem may need to allocate some data structure, for example.
And the VM cannot mark the pte dirty before page_mkwrite, because
page_mkwrite is allowed to fail, so we must not allow any window where the
page could be written to if page_mkwrite does fail.
This solution of holding the page locked over the 3 critical operations
(page_mkwrite, setting the pte dirty, and finally setting the page dirty)
closes out races nicely, preventing page cleaning for writeout being
initiated in that window. This provides the filesystem with a strong
synchronisation against the VM here.
- Sage needs this race closed for ceph filesystem.
- Trond for NFS (http://bugzilla.kernel.org/show_bug.cgi?id=12913).
- I need it for fsblock.
- I suspect other filesystems may need it too (eg. btrfs).
- I have converted buffer.c to the new locking. Even simple block allocation
under dirty pages might be susceptible to i_size changing under partial page
at the end of file (we also have a buffer.c-side problem here, but it cannot
be fixed properly without this patch).
- Other filesystems (eg. NFS, maybe btrfs) will need to change their
page_mkwrite functions themselves.
[ This also moves page_mkwrite another step closer to fault, which should
eventually allow page_mkwrite to be moved into ->fault, and thus avoiding a
filesystem calldown and page lock/unlock cycle in __do_fault. ]
[akpm@linux-foundation.org: fix derefs of NULL ->mapping]
Cc: Sage Weil <sage@newdream.net>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-05-01 06:08:16 +08:00
|
|
|
->fault() is called when a previously not present pte is about
|
|
|
|
|
to be faulted in. The filesystem must find and return the page associated
|
|
|
|
|
with the passed in "pgoff" in the vm_fault structure. If it is possible that
|
|
|
|
|
the page may be truncated and/or invalidated, then the filesystem must lock
|
|
|
|
|
the page, then ensure it is not already truncated (the page lock will block
|
|
|
|
|
subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
|
|
|
|
|
locked. The VM will unlock the page.
|
|
|
|
|
|
|
|
|
|
->page_mkwrite() is called when a previously read-only pte is
|
|
|
|
|
about to become writeable. The filesystem again must ensure that there are
|
|
|
|
|
no truncate/invalidate races, and then return with the page locked. If
|
|
|
|
|
the page has been truncated, the filesystem should not look up a new page
|
|
|
|
|
like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
|
|
|
|
|
will cause the VM to retry the fault.
|
2005-04-17 06:20:36 +08:00
|
|
|
|
2008-07-24 12:27:05 +08:00
|
|
|
->access() is called when get_user_pages() fails in
|
|
|
|
|
acces_process_vm(), typically used to debug a process through
|
|
|
|
|
/proc/pid/mem or ptrace. This function is needed only for
|
|
|
|
|
VM_IO | VM_PFNMAP VMAs.
|
|
|
|
|
|
2005-04-17 06:20:36 +08:00
|
|
|
================================================================================
|
|
|
|
|
Dubious stuff
|
|
|
|
|
|
|
|
|
|
(if you break something or notice that it is broken and do not fix it yourself
|
|
|
|
|
- at least put it here)
|