Re: [PATCH v11 3/5] virtio-blk: do not merge writes across a zone boundary

[Niklas Cassel <cassel@kernel.org>]

Hello Stefan,

On Wed, Jun 03, 2026 at 04:41:50PM -0400, Stefan Hajnoczi wrote:
> On Mon, Jun 01, 2026 at 11:44:03PM +0200, Sam Li wrote:
> > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > index 9cb9f1fb2b..285db19ac7 100644
> > --- a/hw/block/virtio-blk.c
> > +++ b/hw/block/virtio-blk.c
> > @@ -303,17 +306,34 @@ static void virtio_blk_submit_multireq(VirtIOBlock *s, MultiReqBuffer *mrb)
> >      for (i = 0; i < mrb->num_reqs; i++) {
> >          VirtIOBlockReq *req = mrb->reqs[i];
> >          if (num_reqs > 0) {
> > +            zone_cross = false;
> > +
> > +            /*
> > +             * On zoned backends, a single backend write must not span a zone
> 
> This code handles both reads and writes but the comment only mentions
> writes. I think reads are allowed to span zones, so should there be a
> check that mrb->is_write?

From the Virtual I/O Device (VIRTIO) Version 1.4 specification:

"If a VIRTIO_BLK_T_ZONE_APPEND request, a VIRTIO_BLK_T_IN request or a
VIRTIO_BLK_T_OUT request issued to a SWR zone has the range that has
sectors in more than one zone, then the request SHALL be completed with
VIRTIO_BLK_S_ZONE_INVALID_CMD value in the field status."


Thus, while this is allowed to read past the zone boundary in many zoned
specifications, e.g. in both ZAC and ZBC, when the "Read Across Zone
Boundaries bit" is set, is seems like it is never allowed to do so in
VIRTIO.


Kind regards,
Niklas