On Fri, Apr 5, 2024 at 3:20 PM Wafer <wa...@jaguarmicro.com> wrote:
>
> If a virtio-net device has the VIRTIO_NET_F_MRG_RXBUF feature
> but not the VIRTIO_RING_F_INDIRECT_DESC feature,
> 'VirtIONetQueue->rx_vq' will use the merge feature
> to store data in multiple 'elems'.
> The 'num_buffers' in the virtio header indicates how many elements are merged.
> If the value of 'num_buffers' is greater than 1,
> all the merged elements will be filled into the descriptor ring.
> The 'idx' of the elements should be the value of 'vq->used_idx' plus 'ndescs'.
>
> Fixes: 86044b24e8 ("virtio: basic packed virtqueue support")
Acked-by: Eugenio Pérez <epere...@redhat.com>
> Signed-off-by: Wafer <wa...@jaguarmicro.com>
>
> ---
> Changes in v3:
> - Add the commit-ID of the introduced problem in commit message;
>
> Changes in v2:
> - Clarify more in commit message;
> ---
> hw/virtio/virtio.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index fb6b4ccd83..cab5832cac 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -957,12 +957,20 @@ static void virtqueue_packed_flush(VirtQueue *vq,
> unsigned int count)
> return;
> }
>
> + /*
> + * For indirect element's 'ndescs' is 1.
> + * For all other elemment's 'ndescs' is the
> + * number of descriptors chained by NEXT (as set in
> virtqueue_packed_pop).
> + * So When the 'elem' be filled into the descriptor ring,
> + * The 'idx' of this 'elem' shall be
> + * the value of 'vq->used_idx' plus the 'ndescs'.
> + */
> + ndescs += vq->used_elems[0].ndescs;
> for (i = 1; i < count; i++) {
> - virtqueue_packed_fill_desc(vq, &vq->used_elems[i], i, false);
> + virtqueue_packed_fill_desc(vq, &vq->used_elems[i], ndescs, false);
> ndescs += vq->used_elems[i].ndescs;
> }
> virtqueue_packed_fill_desc(vq, &vq->used_elems[0], 0, true);
> - ndescs += vq->used_elems[0].ndescs;
>
> vq->inuse -= ndescs;
> vq->used_idx += ndescs;
> --
> 2.27.0
>
