> On 5 Dec 2016, at 23:42, Eric Blake <ebl...@redhat.com> wrote: > > While not directly related to NBD_CMD_WRITE_ZEROES, the qemu > team discovered that it is useful if a server can advertise > whether an export is in a known-all-zeroes state at the time > the client connects.
I think this is good to go, and ... > Signed-off-by: Eric Blake <ebl...@redhat.com> > --- > doc/proto.md | 5 +++++ > 1 file changed, 5 insertions(+) > > This replaces the following qemu patch attempt: > https://lists.gnu.org/archive/html/qemu-devel/2016-12/msg00357.html > which tried to add NBD_CMD_HAS_ZERO_INIT with poor semantics. The > semantics in this proposal should be much better. > > Patch is to the merge of the master branch and the > extension-write-zeroes branch. By the way, qemu 2.8 is due > to be released "real soon now", and implements NBD_CMD_WRITE_ZEROES, > so maybe it is time to consider promoting the extension-write-zeroes > branch into master. I would support this. In fact the patch is sufficiently simple I think I'd merge this into extension-write-zeroes then merge that into master. Wouter? Alex > diff --git a/doc/proto.md b/doc/proto.md > index afe71fc..7e4ec7f 100644 > --- a/doc/proto.md > +++ b/doc/proto.md > @@ -697,6 +697,11 @@ The field has the following format: > the export. > - bit 9, `NBD_FLAG_SEND_BLOCK_STATUS`: defined by the experimental > `BLOCK_STATUS` > [extension](https://github.com/NetworkBlockDevice/nbd/blob/extension-blockstatus/doc/proto.md). > +- bit 10, `NBD_FLAG_INIT_ZEROES`: Indicates that the server guarantees > + that at the time transmission phase begins, all offsets within the > + export read as zero bytes. Clients MAY use this information to > + avoid writing to sections of the export that should still read as > + zero after the client is done writing. > > Clients SHOULD ignore unknown flags. > > -- > 2.9.3 > > > ------------------------------------------------------------------------------ > Developer Access Program for Intel Xeon Phi Processors > Access to Intel Xeon Phi processor-based developer platforms. > With one year of Intel Parallel Studio XE. > Training and support from Colfax. > Order your platform today.http://sdm.link/xeonphi > _______________________________________________ > Nbd-general mailing list > nbd-gene...@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/nbd-general > -- Alex Bligh
