On Sep 28, 2015 5:34 PM, "Kevin Wolf" <kw...@redhat.com> wrote: > > Am 28.09.2015 um 05:29 hat Jeff Cody geschrieben: > > During mirror, if the target device does not have support zero > > initialization, a mirror may result in a corrupt image. > > > > For instance, on mirror to a host device with format = raw, whatever > > random data is on the target device will still be there for unallocated > > sectors. > > > > This is because during the mirror, we set the dirty bitmap to copy only > > sectors allocated above 'base'. In the case of target devices where we > > cannot assume unallocated sectors will be read as zeroes, we need to > > explicitely zero out this data. > > > > In order to avoid zeroing out all sectors of the target device prior to > > mirroring, we do zeroing as part of the block job. A second dirty > > bitmap cache is created, to track sectors that are unallocated above > > 'base'. These sectors are then checked for status of BDRV_BLOCK_ZERO > > on the target - if they are not, then zeroes are explicitly written. > > > > This only occurs under two conditions: > > > > 1. 'mode' != "existing" > > 2. bdrv_has_zero_init(target) == NULL > > > > We perform the mirroring through mirror_iteration() as before, except > > in two passes. If the above two conditions are met, the first pass > > is using the bitmap tracking unallocated sectors, to write the needed > > zeroes. Then, the second pass is performed, to mirror the actual data > > as before. > > > > If the above two conditions are not met, then the first pass is skipped, > > and only the second pass (the one with the actual data) is performed. > > > > Signed-off-by: Jeff Cody <jc...@redhat.com> > > Also, this makes qemu-iotests 097 fail for me. >
OK, thanks - I'll check that out tomorrow afternoon. I ran iotests on all the tests I thought dealt with mirror, but I must have missed that one with my grep. Jeff
