On Thu, May 31, 2018 at 11:53:26PM +0000, Liu, Changpeng wrote: > > > > -----Original Message----- > > From: Stefan Hajnoczi [mailto:stefanha@xxxxxxxxxx] > > Sent: Thursday, May 31, 2018 6:31 PM > > To: Liu, Changpeng <changpeng.liu@xxxxxxxxx> > > Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; cavery@xxxxxxxxxx; > > jasowang@xxxxxxxxxx; pbonzini@xxxxxxxxxx; Wang, Wei W > > <wei.w.wang@xxxxxxxxx> > > 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); ... > 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.
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