On Wed, Jul 28, 2021 at 08:37:45AM +1000, NeilBrown wrote:

This patch introduces the concept of an "internal" mount which is a
mount where a filesystem has create the mount itself.

Both the mounted-on-dentry and the mount's root dentry must refer to the
same superblock (they may be the same dentry), and the mounted-on dentry
must be an automount.

And what happens if you mount --move it?