Am 25.02.2014 14:41, schrieb Kevin Wolf: > Am 24.02.2014 um 14:01 hat Peter Lieven geschrieben: >> On 24.02.2014 11:38, Paolo Bonzini wrote: >>> Il 24/02/2014 11:26, Peter Lieven ha scritto: >>>> I personally do not need this for QCOW2 but for iSCSI. Here the >>>> optimization >>>> is basically saved bandwidth since a zero write becomes a WRITESAME. >>> It saves bandwidth, but at the potential cost of extra host CPU >>> utilization. I would be fine with having this automatically, but >>> drv->bdrv_co_write_zeroes is not the right check because it is >>> true for qcow2 and raw formats. Something using bdrv_get_info is >>> probably better, because it would have fewer or no false >>> positives. >>> >>>> In all cases if unmap=on it would additionally save disk space. >>> It would also cause worse performance though. I think the automatic >>> addition BDRV_REQ_MAY_UNMAP is what should be a separate option. Perhaps >>> you can have a three-state option, detect-zeros=no/yes/unmap. >> What would be the desired way to store this flag in the BlockDriverState? > Some new enum field? Is there an already implemented example where I can copy from? Its quite diffucult to search through all the involved functions when doing it for the first time.
Peter