| Message ID | 1426053572-21326-3-git-send-email-rusty@rustcorp.com.au |
|---|---|
| State | New |
| Headers | show |
On Wed, Mar 11, 2015 at 04:29:32PM +1030, Rusty Russell wrote: > We only fill in the 'req->qiov.size' bytes on a (successful) read, > not on a write. > > Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> > --- > hw/block/virtio-blk.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c > index 258bb4c..98d87a9 100644 > --- a/hw/block/virtio-blk.c > +++ b/hw/block/virtio-blk.c > @@ -50,11 +50,19 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req, > { > VirtIOBlock *s = req->dev; > VirtIODevice *vdev = VIRTIO_DEVICE(s); > + int type = virtio_ldl_p(VIRTIO_DEVICE(req->dev), &req->out.type); > > trace_virtio_blk_req_complete(req, status); > > stb_p(&req->in->status, status); > - virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in)); > + > + /* If we didn't succeed, we *may* have written more, but don't > + * count on it. */ I wonder about this. So length as you specify it is <= actually written length. What are the advantages of this approach? How about we do the reverse, specify that the length in descriptor is >= the size actually written? If we do this, all these buggy hosts suddenly become correct, which seems better. > + if (type == VIRTIO_BLK_T_IN && status == VIRTIO_BLK_S_OK) { > + virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in)); > + } else { > + virtqueue_push(s->vq, &req->elem, sizeof(*req->in)); > + } > virtio_notify(vdev, s->vq); > } > > -- > 2.1.0
"Michael S. Tsirkin" <mst@redhat.com> writes: > On Wed, Mar 11, 2015 at 04:29:32PM +1030, Rusty Russell wrote: >> We only fill in the 'req->qiov.size' bytes on a (successful) read, >> not on a write. >> >> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> >> --- >> hw/block/virtio-blk.c | 10 +++++++++- >> 1 file changed, 9 insertions(+), 1 deletion(-) >> >> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c >> index 258bb4c..98d87a9 100644 >> --- a/hw/block/virtio-blk.c >> +++ b/hw/block/virtio-blk.c >> @@ -50,11 +50,19 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req, >> { >> VirtIOBlock *s = req->dev; >> VirtIODevice *vdev = VIRTIO_DEVICE(s); >> + int type = virtio_ldl_p(VIRTIO_DEVICE(req->dev), &req->out.type); >> >> trace_virtio_blk_req_complete(req, status); >> >> stb_p(&req->in->status, status); >> - virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in)); >> + >> + /* If we didn't succeed, we *may* have written more, but don't >> + * count on it. */ > > I wonder about this. > So length as you specify it is <= actually written length. > What are the advantages of this approach? > How about we do the reverse, specify that the length in descriptor > is >= the size actually written? > > If we do this, all these buggy hosts suddenly become correct, > which seems better. The point of telling the guest the amount written is that they don't have to zero the receive buffer beforehand. Cheers, Rusty.
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c index 258bb4c..98d87a9 100644 --- a/hw/block/virtio-blk.c +++ b/hw/block/virtio-blk.c @@ -50,11 +50,19 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req, { VirtIOBlock *s = req->dev; VirtIODevice *vdev = VIRTIO_DEVICE(s); + int type = virtio_ldl_p(VIRTIO_DEVICE(req->dev), &req->out.type); trace_virtio_blk_req_complete(req, status); stb_p(&req->in->status, status); - virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in)); + + /* If we didn't succeed, we *may* have written more, but don't + * count on it. */ + if (type == VIRTIO_BLK_T_IN && status == VIRTIO_BLK_S_OK) { + virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in)); + } else { + virtqueue_push(s->vq, &req->elem, sizeof(*req->in)); + } virtio_notify(vdev, s->vq); }
We only fill in the 'req->qiov.size' bytes on a (successful) read, not on a write. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> --- hw/block/virtio-blk.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)