fsnotify: Infrastructure for per-mount watches

Per-mount watches allow groups to listen to fsnotify events on an entire
mount.  This patch simply adds and initializes the fields needed in the
vfsmount struct to make this happen.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Signed-off-by: Eric Paris <eparis@redhat.com>

fs/namespace.c

@@ -614,6 +614,7 @@ static inline void __mntput(struct vfsmount *mnt)
 	 * provides barriers, so count_mnt_writers() below is safe.  AV
 	 */
 	WARN_ON(count_mnt_writers(mnt));
+	fsnotify_vfsmount_delete(mnt);
 	dput(mnt->mnt_root);
 	free_vfsmnt(mnt);
 	deactivate_super(sb);