Il 04/07/2013 23:07, Peter Lieven ha scritto: > > Am 04.07.2013 um 14:37 schrieb Paolo Bonzini <pbonz...@redhat.com>: > >> Il 03/07/2013 23:23, Peter Lieven ha scritto: >>> BDC is not used. I had an implementation that sent multiple descriptors >>> out, but >>> at least for my storage the maximum unmap counts not for each descriptors, >>> but for all >>> together. So in this case we do not need the field at all. I forgot to >>> remove it. >>> >>> discard and write_zeroes will both only send one request up to max_unmap in >>> size. >>> >>> apropos write_zeroes: do you know if UNMAP is guaranteed to unmap data if >>> lbprz == 1? >> >> Yes. On the other hand note that WRITE_SAME should be guaranteed _not_ >> to unmap if lbprz == 0 and you do WRITE_SAME with UNMAP and a zero >> payload, but I suspect there may be buggy targets here. >> >>> I have read in the specs something that the target might unmap the blocks >>> or not touch them at all. >>> Maybe you have more information. >> >> That's even true of UNMAP itself, actually. :) >> >> The storage can always "upgrade" a block from unmapped to anchored and >> from anchored to allocated, so UNMAP can be a no-op and still comply >> with the standard. > > My concern was, if I UNMAP a block and lbprz == 1 is it guaranteed that it > reads > as zero afterwards? Regardless if the target decides to "upgrade" the block > or do > not unmap the block?
I would be very surprised, but if you are worried about that, it definitely won't happen with WRITE_SAME. Paolo
