On Thu, Apr 08, 2010 at 08:51:42AM -0700, David Brown
wrote:> I am developing backup software (<http://github.com/d3zd3z/jpool> for
> the curious), and have been doing some testing with btrfs.
>
> Jpool currently uses the blkid database to map between device numbers
> (st_rdev) and the uuid of a particular filesystem. I originally
> created this because LVM device numbers sometimes changed. Jpool
> uses the uuid to track files within a tree.
>
> The subvolumes on btrfs seem to be getting ephemeral device numbers,
> which aren''t listed in the blkid output. The program falls back
to
> using the mountpoint, but that misses mountpoints changing.
>
> - Do subvolumes in btrfs even have separate uuids, and should they?
I think yes, in libblkid code is:
blkid_probe_set_uuid(pr, bfs->fsid);
blkid_probe_set_uuid_as(pr, bfs->dev_item.uuid, "UUID_SUB");
so there should be two UUIDs for the device.
However, I''d like to see more information about btrfs UUIDs.
BTW, see my old discussion with Andreas about UUIDs:
http://marc.info/?l=linux-fsdevel&m=126754081900406&w=2
Karel
--
Karel Zak <kzak@redhat.com>
http://karelzak.blogspot.com
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