[PATCH v2 2/3] virtio_net: Handle _F_STATUS emulation in virtio_net_get_config

["Eugenio Pérez" <eperezma@redhat.com>]

At this moment this code path is not reached, but vdpa devices can offer
VIRTIO_NET_F_STATUS unconditionally. While the guest must assume that
link is always up by the standard, qemu will set the status bit to 1
always in this case.

This makes little use by itself, but VIRTIO_NET_F_STATUS is needed for
the guest to read status bit VIRTIO_NET_F_GUEST_ANNOUNCE, used by feature
VIRTIO_NET_F_GUEST_ANNOUNCE. So qemu must emulate status feature in case
it needs to emulate the guest announce feature.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/net/virtio-net.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 56ff219196..6d4d75615b 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -156,8 +156,9 @@ static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
      * disconnect/reconnect a VDPA peer.
      */
     if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
-        ret = vhost_net_get_config(get_vhost_net(nc->peer), (uint8_t *)&netcfg,
-                                   n->config_size);
+        struct vhost_net *net = get_vhost_net(nc->peer);
+
+        ret = vhost_net_get_config(net, (uint8_t *)&netcfg, n->config_size);
         if (ret == -1) {
             return;
         }
@@ -173,6 +174,12 @@ static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
             memcpy(netcfg.mac, n->mac, ETH_ALEN);
         }
 
+        if (vdev->guest_features & BIT_ULL(VIRTIO_NET_F_STATUS) &&
+            !(net->dev.features & BIT_ULL(VIRTIO_NET_F_STATUS))) {
+            /* Emulating link up in qemu */
+            netcfg.status |= virtio_tswap16(vdev, VIRTIO_NET_S_LINK_UP);
+        }
+
         memcpy(config, &netcfg, n->config_size);
     }
 }
-- 
2.31.1