VFS: Comment mount following code

Add comments describing what the directions "up" and "down" mean and ref count
handling to the VFS mount following family of functions.

Signed-off-by: Valerie Aurora <vaurora@redhat.com> (Original author)
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 14 insertions, 2 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index be1b07a774f1..c53d3381b0d0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -515,8 +515,20 @@ struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
 }
 
 /*
- * lookup_mnt increments the ref count before returning
- * the vfsmount struct.
+ * lookup_mnt - Return the first child mount mounted at path
+ *
+ * "First" means first mounted chronologically.  If you create the
+ * following mounts:
+ *
+ * mount /dev/sda1 /mnt
+ * mount /dev/sda2 /mnt
+ * mount /dev/sda3 /mnt
+ *
+ * Then lookup_mnt() on the base /mnt dentry in the root mount will
+ * return successively the root dentry and vfsmount of /dev/sda1, then
+ * /dev/sda2, then /dev/sda3, then NULL.
+ *
+ * lookup_mnt takes a reference to the found vfsmount.
  */
 struct vfsmount *lookup_mnt(struct path *path)
 {