On 02/27/2012 04:24 PM, Anthony Liguori wrote: > > Then you get an error with the block devices still frozen. You can > execute another command to reopen back to the old image to roll back the > transaction. > > Pushing the rollback logic to the client does make the client interface > a bit more complicated and adds latency to the error path but it's much > easier than building a complex transaction infrastructure. > > And there are examples of this in the wild too. LDAP uses a similar > mechanism.
Actually, have you seen Jeff's atomic snapshot patch? It really implements all that is needed to do transactions, and gets 100% ok error-recovery unlike the existing blockdev_snapshot_sync. It really looks like we can do better than client-side error management, and there is not that much complexity at all. Jeff could rework his patches to work with transaction begin/commit commands, and Federico can then add drive-reopen and drive-migrate on top. Paolo
