From: Akihiko Odaki <akihiko.odaki@daynix.com>

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>
Message-Id: <20250108-buffers-v1-1-a0c85ff31aeb@daynix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit c17ad4b11bd268a35506cd976884562df6ca69d7)
(Mjt: adjust for 7.2.x)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 204a80ec71..0ba1db5b14 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1914,6 +1914,8 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
                                     sg, elem->in_num,
                                     offsetof(typeof(mhdr), num_buffers),
                                     sizeof(mhdr.num_buffers));
+            } else {
+                mhdr.num_buffers = cpu_to_le16(1);
             }
 
             receive_header(n, sg, elem->in_num, buf, size);
-- 
2.39.5