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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 <[email protected]>
Signed-off-by: Al Viro <[email protected]>
This commit is contained in:
David Howells 2011-01-14 19:10:03 +00:00 • committed by Al Viro
commit ea5b778a8b
8 changed files with 101 additions and 89 deletions
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25
fs/afs/mntpt.c
View file

@ -241,7 +241,6 @@ error_no_devname:
struct vfsmount *afs_d_automount(struct path *path)
{
struct vfsmount *newmnt;
int err;
_enter("{%s,%s}", path->mnt->mnt_devname, path->dentry->d_name.name);
@ -249,24 +248,12 @@ struct vfsmount *afs_d_automount(struct path *path)
if (IS_ERR(newmnt))
return newmnt;
mntget(newmnt);
err = do_add_mount(newmnt, path, MNT_SHRINKABLE, &afs_vfsmounts);
switch (err) {
case 0:
queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer,
afs_mntpt_expiry_timeout * HZ);
_leave(" = %p {%s}", newmnt, newmnt->mnt_devname);
return newmnt;
case -EBUSY:
/* someone else made a mount here whilst we were busy */
mntput(newmnt);
_leave(" = NULL [EBUSY]");
return NULL;
default:
mntput(newmnt);
_leave(" = %d", err);
return ERR_PTR(err);
}
mntget(newmnt); /* prevent immediate expiration */
mnt_set_expiry(newmnt, &afs_vfsmounts);
queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer,
afs_mntpt_expiry_timeout * HZ);
_leave(" = %p {%s}", newmnt, newmnt->mnt_devname);
return newmnt;
}
/*