[linux-cifs-client] DFS support in CIFS

[Steve French]

It is interesting now that "fs_locations" support is in Linux NFSv4 
client.   They do it via "implicit mount" approach, rather than 
overriding inode backpointers to the superblock and have addressed the 
issue of umount.

See fs/nfs/nfs4namespace.c and other places that call vfs_kern_mount and 
afs/mntpt.c

For umount nfs handles the implicit mounts which need to be implicitly 
umounted in shrink_submounts