virtio: Enable netpoll interface for netconsole logging

Add a new poll_controller handler that the netpoll interface needs.

This enables netconsole logging from a kvm guest over the virtio
net interface.
Signed-off-by: Amit Shah <amitshah@gmx.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/net/virtio_net.c

@@ -294,6 +294,15 @@ again:
 	return 0;
 }
 
+#ifdef CONFIG_NET_POLL_CONTROLLER
+static void virtnet_netpoll(struct net_device *dev)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+
+	napi_schedule(&vi->napi);
+}
+#endif
+
 static int virtnet_open(struct net_device *dev)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
@@ -336,6 +345,9 @@ static int virtnet_probe(struct virtio_device *vdev)
 	dev->stop = virtnet_close;
 	dev->hard_start_xmit = start_xmit;
 	dev->features = NETIF_F_HIGHDMA;
+#ifdef CONFIG_NET_POLL_CONTROLLER
+	dev->poll_controller = virtnet_netpoll;
+#endif
 	SET_NETDEV_DEV(dev, &vdev->dev);
 
 	/* Do we support "hardware" checksums? */