Btrfs devel - Nov 2009 - To loop or not to loop with btrfs

Hi,


This left me puzzled for a while:

22:29 borg:/ # losetup /dev/loop1 /.B.disk
22:29 borg:/ # mount /dev/loop1 /B
mount: /dev/loop1: can''t read superblock
22:29 borg:/ # blkid /dev/loop1
/dev/loop1: UUID="e19fe89b-cde3-4ccc-bc70-b759a57bd1c9"
UUID_SUB="f29c6218-d040-4546-a227-4dd2d2142817" TYPE="btrfs"
22:29 borg:/ # losetup -d /dev/loop1
22:29 borg:/ # losetup /dev/loop2 /.B.disk 
22:29 borg:/ # mount /dev/loop2 /B
(success)

So the btrfs volume is tied to loop2? That certainly is not good.
Even real disks (/dev/sd*) can move around, the more so USB flash
gadgets and loop devices.
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On Wed, Nov 18, 2009 at 10:31:53PM +0100, Jan Engelhardt
wrote:
> This left me puzzled for a while:
> 
> 22:29 borg:/ # losetup /dev/loop1 /.B.disk
> 22:29 borg:/ # mount /dev/loop1 /B
> mount: /dev/loop1: can''t read superblock
> 22:29 borg:/ # blkid /dev/loop1
> /dev/loop1: UUID="e19fe89b-cde3-4ccc-bc70-b759a57bd1c9"
> UUID_SUB="f29c6218-d040-4546-a227-4dd2d2142817"
TYPE="btrfs"
> 22:29 borg:/ # losetup -d /dev/loop1
> 22:29 borg:/ # losetup /dev/loop2 /.B.disk 
> 22:29 borg:/ # mount /dev/loop2 /B
> (success)
> 
> So the btrfs volume is tied to loop2? That certainly is not good.
> Even real disks (/dev/sd*) can move around, the more so USB flash
> gadgets and loop devices.
   This looks like it might be related to [1]? (I suspect it slipped
Chris''s mind back in April, and nobody''s really noticed it
since).

   Hugo.

[1] http://article.gmane.org/gmane.comp.file-systems.btrfs/2817

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