On 11/10/2016 00:51, John Snow wrote:
>> Clearing the bitmap is a bug because the caller could expect that the
>> bitmap is in its original state if the transaction fails. I doubt this
>> is a problem in practice, but we should fix it anyway.
> We make a backup to undo the process if it fails. I only mention it to
> emphasize that the atomic point appears to be during prepare. In
> practice we hold the locks for the whole process, but... I think Paolo
> may be actively trying to change that.
Even now, atomicity must be ensured with bdrv_drained_begin/end. The
AioContext lock does not promise atomicity.