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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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41
fs/namespace.c
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@@ -1925,15 +1925,14 @@ static int do_new_mount(struct path *path, char *type, int flags,
if (IS_ERR(mnt))
return PTR_ERR(mnt);
return do_add_mount(mnt, path, mnt_flags, NULL);
return do_add_mount(mnt, path, mnt_flags);
}
/*
* add a mount into a namespace's mount tree
* - provide the option of adding the new mount to an expiration list
* - this unconditionally eats one of the caller's references to newmnt.
*/
int do_add_mount(struct vfsmount *newmnt, struct path *path,
int mnt_flags, struct list_head *fslist)
int do_add_mount(struct vfsmount *newmnt, struct path *path, int mnt_flags)
{
int err;
@@ -1963,9 +1962,6 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path,
if ((err = graft_tree(newmnt, path)))
goto unlock;
if (fslist) /* add to the specified expiration list */
list_add_tail(&newmnt->mnt_expire, fslist);
up_write(&namespace_sem);
return 0;
@@ -1975,7 +1971,36 @@ unlock:
return err;
}
EXPORT_SYMBOL_GPL(do_add_mount);
/**
* mnt_set_expiry - Put a mount on an expiration list
* @mnt: The mount to list.
* @expiry_list: The list to add the mount to.
*/
void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
{
down_write(&namespace_sem);
br_write_lock(vfsmount_lock);
list_add_tail(&mnt->mnt_expire, expiry_list);
br_write_unlock(vfsmount_lock);
up_write(&namespace_sem);
}
EXPORT_SYMBOL(mnt_set_expiry);
/*
* Remove a vfsmount from any expiration list it may be on
*/
void mnt_clear_expiry(struct vfsmount *mnt)
{
if (!list_empty(&mnt->mnt_expire)) {
down_write(&namespace_sem);
br_write_lock(vfsmount_lock);
list_del_init(&mnt->mnt_expire);
br_write_unlock(vfsmount_lock);
up_write(&namespace_sem);
}
}
/*
* process a list of expirable mountpoints with the intent of discarding any