[Sheepdog] [PATCH RFC v3] Introduce block driver claim and release hooks

[MORITA Kazutaka]

On 11/27/2009 10:43 PM, Chris Webb wrote:
> During live migration, block drivers with exclusive locking behaviour [such as
> Sheepdog: http://www.osrg.net/sheepdog/] are problematic, as both source and
> destination need to have the device open simultaneously. However, the lock is
> only required while the vm is running, and at most one vm is running at each
> stage of migration. This patch introduces bdrv_claim and bdrv_release hooks
> which can be used to claim and release the lock on vm start and stop, allowing
> Sheepdog-backed guests to migrate.
> 
> This functionality could also be more generally useful. For example, it would
> be possible to take fcntl() locks on qcow2 files, preventing corruption from
> two qemu processes concurrently modifying qcow2 metadata. Doing this in
> bdrv_open() is not possible as it would prevent live migration of guests
> backed by qcow2 files on a shared filesystem.

We may need to discuss this patch in qemu-devel, but this is enough
useful for sheepdog to support live migration, so I'll merge it.
Thanks, Chris!

Regards,

MORITA Kazutaka