> -----Original Message-----
> From: Stefan Hajnoczi [mailto:stefa...@redhat.com]
> Sent: Friday, June 1, 2018 5:00 PM
> To: Liu, Changpeng <changpeng....@intel.com>
> Cc: virtualization@lists.linux-foundation.org; cav...@redhat.com;
> jasow...@redhat.com; pbonz...@redhat.com; Wang, Wei W
> <wei.w.w...@intel.com>
> Subject: Re: [PATCH v4] virtio_blk: add DISCARD and WRIET ZEROES commands
> support
>
> On Thu, May 31, 2018 at 11:53:26PM +0000, Liu, Changpeng wrote:
> >
> >
> > > -----Original Message-----
> > > From: Stefan Hajnoczi [mailto:stefa...@redhat.com]
> > > Sent: Thursday, May 31, 2018 6:31 PM
> > > To: Liu, Changpeng <changpeng....@intel.com>
> > > Cc: virtualization@lists.linux-foundation.org; cav...@redhat.com;
> > > jasow...@redhat.com; pbonz...@redhat.com; Wang, Wei W
> > > <wei.w.w...@intel.com>
> > > Subject: Re: [PATCH v4] virtio_blk: add DISCARD and WRIET ZEROES commands
> > > support
> > >
> > > On Tue, May 29, 2018 at 09:42:24AM +0800, Changpeng Liu wrote:
> > > > num = blk_rq_map_sg(hctx->queue, req, vbr->sg);
> > > > if (num) {
> > > > - if (rq_data_dir(req) == WRITE)
> > > > + if (rq_data_dir(req) == WRITE || type ==
> > > > VIRTIO_BLK_T_DISCARD
> > > ||
> > > > + type == VIRTIO_BLK_T_WRITE_ZEROES)
> > > > vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev,
> > > VIRTIO_BLK_T_OUT);
> > >
> > > The VIRTIO specification says:
> > >
> > > The type of the request is either a read (VIRTIO_BLK_T_IN), a write
> > > (VIRTIO_BLK_T_OUT), a discard (VIRTIO_BLK_T_DISCARD), a write zeroes
> > > (VIRTIO_BLK_T_WRITE_ZEROES) or a flush (VIRTIO_BLK_T_FLUSH).
> > >
> > > But this patch actually uses VIRTIO_BLK_T_DISCARD | VIRTIO_BLK_T_OUT or
> > > VIRTIO_BLK_T_WRITE_ZEROES | VIRTIO_BLK_T_OUT. "either A or B" is
> > > exclusive, it does not mean "A and B".
> > Hi Stefan,
> >
> > For the new add DISCARD and WRITE ZEROES commands, I defined the
> > type code to 11 and 13, so the last bit always is 1, there is no difference
> > in practice.
>
> Then the code is misleading. This is clearer:
>
> if (type == VIRTIO_BLK_T_DISCARD || type == VIRTIO_BLK_T_WRITE_ZEROES)
> /* Do nothing, type already set */
> else if (rq_data_dir(req) == WRITE)
> vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_OUT);
> ...
This change sounds good to me, will change the patch accordingly.
>
> > But I believe the specification says VIRTIO_BLK_T_OUT means direction, so
> > OR the two bits together should compliance with the specification.
>
> I cannot find that in the specification:
>
> http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-
> 2020002
>
> and it would contradict the "The type of the request is either ... or
> ..." wording that I quoted from the spec above.
>
> If you do find something in the spec, please let me know and we can
> figure out how to make the spec consistent.
I saw comments from file linux/usr/include/uapi/linux/virtio_blk.h, which says
VIRTIO_BLK_T_OUT may be combined with other commands and means direction,
the specification does not have such description.
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