On 10/31/2016 09:37 AM, Paolo Bonzini wrote: > From: Eric Blake <ebl...@redhat.com> > > Upstream NBD protocol recently added the ability to efficiently > write zeroes without having to send the zeroes over the wire, > along with a flag to control whether the client wants a hole. > > The generic block code takes care of falling back to the obvious > write of lots of zeroes if we return -ENOTSUP because the server > does not have WRITE_ZEROES. > > Ideally, since NBD_CMD_WRITE_ZEROES does not involve any data > over the wire, we want to support transactions that are much > larger than the normal 32M limit imposed on NBD_CMD_WRITE. But > the server may still have a limit smaller than UINT_MAX, so > until experimental NBD protocol additions for advertising various > command sizes is finalized (see [1], [2]), for now we just stick to > the same limits as normal writes. > > [1] https://github.com/yoe/nbd/blob/extension-info/doc/proto.md > [2] https://sourceforge.net/p/nbd/mailman/message/35081223/ > > Signed-off-by: Eric Blake <ebl...@redhat.com> > Message-Id: <1476469998-28592-17-git-send-email-ebl...@redhat.com> > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > --- > block/nbd-client.c | 35 +++++++++++++++++++++++++++++++++++ > block/nbd-client.h | 2 ++ > block/nbd.c | 4 ++++ > 3 files changed, 41 insertions(+)
This patch went through so much rebasing that I failed to realize it was originally written prior to adding commit 465fe887 with its bs->supported_zero_flags. As such, the block layer eats flags and never allows the server to perform FUA or do an unmap. I'll be posting a followup for inclusion in 2.8, alongside my other pending patches (I found it because of blkdebug enhancements that I'm writing, although the blkdebug changes themselves are 2.9 material). -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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