The specification says the device MUST set num_buffers to 1 if
VIRTIO_NET_F_MRG_RXBUF has not been negotiated.

Fixes: df91055db5c9 ("virtio-net: enable virtio 1.0")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 hw/net/virtio-net.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 06f096abf678..b241cd4bb48a 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1992,6 +1992,8 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
                                     offsetof(typeof(hdr),
                                              virtio_net.hdr.num_buffers),
                                     sizeof(hdr.virtio_net.hdr.num_buffers));
+            } else {
+                hdr.virtio_net.hdr.num_buffers = cpu_to_le16(1);
             }
 
             guest_offset = n->has_vnet_hdr ?

---
base-commit: 38d0939b86e2eef6f6a622c6f1f7befda0146595
change-id: 20241227-buffers-6bd3493c287e

Best regards,
-- 
Akihiko Odaki <akihiko.odaki@daynix.com>

I tested this patch with virtio-net regression tests and tests
"mrg_rxbuf" on/off status with netperf tests, everything works fine.

Tested-by: Lei Yang <leiyang@redhat.com>

On Wed, Jan 8, 2025 at 8:23 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>
> The specification says the device MUST set num_buffers to 1 if
> VIRTIO_NET_F_MRG_RXBUF has not been negotiated.
>
> Fixes: df91055db5c9 ("virtio-net: enable virtio 1.0")
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>  hw/net/virtio-net.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 06f096abf678..b241cd4bb48a 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -1992,6 +1992,8 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
>                                      offsetof(typeof(hdr),
>                                               virtio_net.hdr.num_buffers),
>                                      sizeof(hdr.virtio_net.hdr.num_buffers));
> +            } else {
> +                hdr.virtio_net.hdr.num_buffers = cpu_to_le16(1);
>              }
>
>              guest_offset = n->has_vnet_hdr ?
>
> ---
> base-commit: 38d0939b86e2eef6f6a622c6f1f7befda0146595
> change-id: 20241227-buffers-6bd3493c287e
>
> Best regards,
> --
> Akihiko Odaki <akihiko.odaki@daynix.com>
>
>