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Unexport do_add_mount() and add in follow_automount(), not ->d_automount()

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Unexport do_add_mount() and make ->d_automount() return the vfsmount to be
added rather than calling do_add_mount() itself.  follow_automount() will then
do the addition.

This slightly complicates things as ->d_automount() normally wants to add the
new vfsmount to an expiration list and start an expiration timer.  The problem
with that is that the vfsmount will be deleted if it has a refcount of 1 and
the timer will not repeat if the expiration list is empty.

To this end, we require the vfsmount to be returned from d_automount() with a
refcount of (at least) 2.  One of these refs will be dropped unconditionally.
In addition, follow_automount() must get a 3rd ref around the call to
do_add_mount() lest it eat a ref and return an error, leaving the mount we
have open to being expired as we would otherwise have only 1 ref on it.

d_automount() should also add the the vfsmount to the expiration list (by
calling mnt_set_expiry()) and start the expiration timer before returning, if
this mechanism is to be used.  The vfsmount will be unlinked from the
expiration list by follow_automount() if do_add_mount() fails.

This patch also fixes the call to do_add_mount() for AFS to propagate the mount
flags from the parent vfsmount.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
David Howells
2011-01-14 19:10:03 +00:00
committed by Al Viro
parent ab90911ff9
commit ea5b778a8b
8 changed files with 101 additions and 89 deletions
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23
Documentation/filesystems/vfs.txt
View File

@ -933,15 +933,20 @@ struct dentry_operations {
dynamic_dname() helper function is provided to take care of this.
d_automount: called when an automount dentry is to be traversed (optional).
This should create a new VFS mount record, mount it on the directory
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 automount 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.
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