Re: [RFC PATCH] file as directory

[Al Viro <viro@ftp.linux.org.uk>]

On Wed, May 23, 2007 at 09:19:17AM +0200, Miklos Szeredi wrote:
> > Eh...  Arbitrary limitations are fun, aren't they?
> 
> But these mounts _are_ special.  There is really no point in moving or
> pivoting them.

pivoting - probably true, moving... why not?
 
> > What about MNT_SLAVE stuff being set up prior to that lookup?
> 
> These mounts are not propagated.  Or at least I hope so.  Propagation
> stuff is a bit too complicated for my poor little brain.

Er...  These mounts might not be propagated, but what about a bind
over another instance of such file in master tree?
 
> I think they should be the same superblock, same dentry.  What would
> be the advantage of doing otherwise?

Then you are going to have interesting time with locking in final mntput().
BTW, what about having several links to the same file?  You have i_mutex
on the inode, so serialization of those is not a problem, but...
 
> I think doing this recursively should be allowed.  "Releasing last ref
> cleans up the mess" should work in that case.

Releasing the last reference will lead to cascade of umounts in that
case...  IOW, need to be careful with locking.