Re: [PATCH] Improve support for exporting btrfs subvolumes.

[Steve Dickson <SteveD@redhat.com>]

On 06/17/2010 12:54 AM, Neil Brown wrote:
> 
> If you export two subvolumes of a btrfs filesystem, they will both be
> given the same uuid so lookups will be confused.
> blkid cannot differentiate the two, so we must use the fsid from
> statfs64 to identify the filesystem.
> 
> We cannot tell if blkid or statfs is best without knowing internal
> details of the filesystem in question, so we need to encode specific
> knowledge of btrfs in mountd.  This is unfortunate.
> 
> To ensure smooth handling of this and possible future changes in uuid
> generation, we add infrastructure for multiple different uuids to be
> recognised on old filehandles, but only the preferred on is used on
> new filehandles.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> 
> --
> This is a substantially revised version of a patch I posted a while
> ago.
> I tried to find a way to do it would hard coding knowledge of btrfs in
> nfs-utils, but it isn't possible.  For some filesystems, f_fsid is
> best, for some it is worst.  No way to tell the difference.
> 
> This patch add infrastructure so that if we find a better way to get a
> good uuid (e.g. a new syscall), we can slot it in for new filehandles,
> but old filehandles using the old uuid will still work.
> 
> I believe this is ready for inclusion upstream.

Committed...

steved.