virtio-net: support changing the number of queue pairs through ethtool

This patch implements the ethtool_{set|get}_channels method of virtio-net to
allow user to change the number of queues when the device is running on demand.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -1075,10 +1075,53 @@ static void virtnet_get_drvinfo(struct net_device *dev,
 
 }
 
+/* TODO: Eliminate OOO packets during switching */
+static int virtnet_set_channels(struct net_device *dev,
+				struct ethtool_channels *channels)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+	u16 queue_pairs = channels->combined_count;
+	int err;
+
+	/* We don't support separate rx/tx channels.
+	 * We don't allow setting 'other' channels.
+	 */
+	if (channels->rx_count || channels->tx_count || channels->other_count)
+		return -EINVAL;
+
+	if (queue_pairs > vi->max_queue_pairs)
+		return -EINVAL;
+
+	err = virtnet_set_queues(vi, queue_pairs);
+	if (!err) {
+		netif_set_real_num_tx_queues(dev, queue_pairs);
+		netif_set_real_num_rx_queues(dev, queue_pairs);
+
+		virtnet_set_affinity(vi, true);
+	}
+
+	return err;
+}
+
+static void virtnet_get_channels(struct net_device *dev,
+				 struct ethtool_channels *channels)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+
+	channels->combined_count = vi->curr_queue_pairs;
+	channels->max_combined = vi->max_queue_pairs;
+	channels->max_other = 0;
+	channels->rx_count = 0;
+	channels->tx_count = 0;
+	channels->other_count = 0;
+}
+
 static const struct ethtool_ops virtnet_ethtool_ops = {
 	.get_drvinfo = virtnet_get_drvinfo,
 	.get_link = ethtool_op_get_link,
 	.get_ringparam = virtnet_get_ringparam,
+	.set_channels = virtnet_set_channels,
+	.get_channels = virtnet_get_channels,
 };
 
 #define MIN_MTU 68