Hi Ian, Al,
I've done some updating to consolidate the patches and update the
documentation. I've also added a patch to attempt to make d_manage() capable
of handling RCU-walk (can you test that Ian?).
The patches are committed to:
http://git.kernel.org/?p=linux/kernel/git/dhowells/linux-2.6-automount.git;a=summary
and should appear there eventually.
---
The attached patches implement VFS support for automounting - which several
filesystems, including autofs, can use to resolve problems with their current
implementations. This means that these filesystems no longer have to abuse
lookup(), follow_link() and d_revalidate() to achieve the desired effects.
Probably the most significant advantage for autofs is a long standing potential
deadlock can be removed which otherwise cannot be resolved.
These patches introduce a couple of new dentry operations for use by
automounters and make AFS, NFS, CIFS and autofs4 use them.
There are two dentry operations provided:
(1) struct vfsmount *(*d_automount)(struct path *path);
This is used by follow_automount() in fs/namei.c to ask the filesystem
that owns the dentry at the current path point to mount something on
@path.
It is called if DCACHE_NEED_AUTOMOUNT (which is propagated from the
S_AUTOMOUNT inode flag) is flagged on a dentry and if that dentry has
nothing mounted on it in the current namespace when someone attempts to
use that dentry.
No locks will be held when this is called.
d_op->d_automount() may return one of:
(a) The vfsmount mounted upon that dentry, in which case pathwalk will
move to the root dentry of that vfsmount. ->d_automount() must have
in some manner mounted this before returning.
(b) NULL if something was already mounted there, in which case pathwalk
will loop around and recheck the mountings.
(c) -EISDIR, in which case pathwalk will stop at this point and attempt to
use that dentry as the object of interest. If the current dentry is
not terminal within the path, -EREMOTE will be returned.
(d) An error value, to be returned immediately.
Automount transits are counted as symlinks to prevent circular references
from being a problem. If one is detected, -ELOOP will be returned.
If stat() is given AT_NO_AUTOMOUNT then d_op->d_automount() will not be
invoked on a terminal dentry; instead that dentry will be returned by
pathwalk.
follow_automount() also does not invoke d_op->d_automount() if the caller
gave AT_SYMLINK_NOFOLLOW to stat(), but rather returns the base dentry.
(2) int (*d_manage)(struct path *path, bool mounting_here);
This is called by managed_dentry() or follow_down() in fs/namei.c to
indicate to a filesystem that pathwalk is about to step off of the current
path point and walk to another point in the path.
This is called if DCACHE_MANAGE_TRANSIT is set on a dentry.
This can then be used by autofs to stop non-daemon processes from walking
until it has finished constructing or expiring the tree behind the dentry.
It could also be used to prevent undesirables from mounting on this
dentry.
@mounting_here is true if called from follow_down() from mount, in which
case namespace_sem is held exclusively by the caller of follow_down().
Otherwise, no locks are held.
d_op->d_manage() may return one of:
(a) 0 to continue the pathwalk as normal.
(b) -EISDIR to prevent managed_dentry() from crossing to a mounted
filesystem or calling d_op->d_automount(), in which case the dentry
will be treated as an ordinary directory.
(c) With the final (and provisional) patch of the series, -ECHILD to ask
the caller to break out of RCU-pathwalk mode (d_manage() acquires a
third parameter which is true if it is being called in RCU-walk
mode).
(d) Another error to abort the pathwalk completely.
To make this work for autofs a couple of additional dentry d_flags have been
defined: DCACHE_MANAGE_TRANSIT and DCACHE_NEED_AUTOMOUNT. This allows
follow_managed() to test all three conditions with minimumal overhead if none
of them are true.
For other filesystems, setting S_AUTOMOUNT is sufficient. This is noted by
d_set_d_op() which will set DCACHE_NEED_AUTOMOUNT automatically if it is seen.
Checking S_AUTOMOUNT doesn't work for autofs, however, since the dentry might
not have an inode, hence why a dentry flag also.
S_AUTOMOUNT and d_automount() are introduced in patch 1; d_manage(),
DCACHE_MANAGE_TRANSIT and DCACHE_NEED_AUTOMOUNT are introduced in patch 7.
=======
UPDATES
=======
[ver #4]
- Rearranged and merged the patches a bit and updated the documentation,
both that to be added into the kernel and the patch descriptions.
- Looked at making d_manage() able to handle RCU-walk mode pathwalk.
[ver #3]
- Update to take account of Nick Piggin's RCU-based pathwalk changes.
[ver #2]
- Fixed a EXDEV in patch 6 to be EISDIR. We were previously using EXDEV to
indicate we wanted to handle a directory as a directory and not to process
it as a mountpoint.
- Move some autofs v4 pseudo mount bits into the v4 pseudo direct mount
patch [patch 16].
- Move a comment fix to the autofs d_automount() patch [patch 10 -> 9].
- Adjust the patch titles of the last three autofs patches.
David
---
David Howells (9):
Allow d_manage() to be used in RCU-walk mode
Remove a further kludge from __do_follow_link()
Remove the automount through follow_link() kludge code from pathwalk
CIFS: Use d_automount() rather than abusing follow_link()
NFS: Use d_automount() rather than abusing follow_link()
AFS: Use d_automount() rather than abusing follow_link()
From: David Howells <dhowe...@redhat.com>
Add a dentry op to allow processes to be held during pathwalk transit
Add a dentry op to handle automounting rather than abusing follow_link()
Ian Kent (9):
autofs4: Bump version
autofs4: Add v4 pseudo direct mount support
autofs4: Fix wait validation
autofs4: Clean up autofs4_free_ino()
autofs4: Clean up dentry operations
autofs4: Clean up inode operations
autofs4: Remove unused code
autofs4: Add d_manage() dentry operation
autofs4: Add d_automount() dentry operation
Documentation/filesystems/Locking | 3
Documentation/filesystems/vfs.txt | 38 ++
drivers/staging/autofs/dirhash.c | 5
fs/afs/dir.c | 1
fs/afs/inode.c | 3
fs/afs/internal.h | 1
fs/afs/mntpt.c | 47 +--
fs/autofs4/autofs_i.h | 100 ++++-
fs/autofs4/dev-ioctl.c | 2
fs/autofs4/expire.c | 51 ++-
fs/autofs4/inode.c | 28 --
fs/autofs4/root.c | 685 ++++++++++++++++---------------------
fs/autofs4/waitq.c | 17 +
fs/cifs/cifs_dfs_ref.c | 134 ++++---
fs/cifs/cifsfs.h | 6
fs/cifs/dir.c | 2
fs/cifs/inode.c | 8
fs/dcache.c | 5
fs/namei.c | 307 +++++++++++++----
fs/namespace.c | 14 -
fs/nfs/dir.c | 4
fs/nfs/inode.c | 4
fs/nfs/internal.h | 1
fs/nfs/namespace.c | 87 ++---
fs/nfsd/vfs.c | 5
fs/stat.c | 4
include/linux/auto_fs4.h | 2
include/linux/dcache.h | 16 +
include/linux/fcntl.h | 1
include/linux/fs.h | 2
include/linux/namei.h | 5
include/linux/nfs_fs.h | 1
32 files changed, 894 insertions(+), 695 deletions(-)
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