Re: [Qemu-devel] [PATCH] virtio-scsi: fix "written length" field in the used ring

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Apr 27, 2015 at 02:29:25PM +0200, Paolo Bonzini wrote:
> qsgl->size is the size of the data field after the request or
> response header (virtio-scsi currently supports only one such
> field; bidirectional requests are not supported).  However,
> the used ring's len field is not concerned about the field
> after the request header, so do not count it unless req->mode
> signals the request was a read.
> 
> Also, do not report that anything was written if the request
> failed, and subtract any residual bytes in case of buffer underrun.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

Pls merge through the storage tree.

Also, can you pls fix up blk similarly?


> ---
>  hw/scsi/virtio-scsi.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index c9bea06..4995f6e 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -65,6 +65,19 @@ void virtio_scsi_free_req(VirtIOSCSIReq *req)
>      g_slice_free1(sizeof(*req) + vs->cdb_size, req);
>  }
>  
> +static size_t virtio_scsi_written_length(VirtIODevice *vdev, VirtIOSCSIReq *req)
> +{
> +    size_t sz = req->resp_iov.size;
> +
> +    if (req->sreq &&
> +        req->mode == SCSI_XFER_FROM_DEV &&
> +        req->resp.cmd.response == VIRTIO_SCSI_S_OK) {
> +        sz += req->qsgl.size - virtio_tswap32(vdev, req->resp.cmd.resid);
> +    }
> +
> +    return sz;
> +}
> +
>  static void virtio_scsi_complete_req(VirtIOSCSIReq *req)
>  {
>      VirtIOSCSI *s = req->dev;
> @@ -76,7 +89,7 @@ static void virtio_scsi_complete_req(VirtIOSCSIReq *req)
>          assert(req->vq == NULL);
>          virtio_scsi_vring_push_notify(req);
>      } else {
> -        virtqueue_push(vq, &req->elem, req->qsgl.size + req->resp_iov.size);
> +        virtqueue_push(vq, &req->elem, virtio_scsi_written_length(vdev, req));
>          virtio_notify(vdev, vq);
>      }
>  
> -- 
> 2.3.5