virtio_net: add ethtool support for set and get of settings

This patch allows the user to set and retrieve speed and duplex of the
virtio_net device via ethtool. Having this functionality is very helpful
for simulating different environments and also enables the virtio_net
device to participate in operations where proper speed and duplex are
required (e.g. currently bonding lacp mode requires full duplex). Custom
speed and duplex are not allowed, the user-supplied settings are validated
before applying.

Example:
$ ethtool eth1
Settings for eth1:
...
	Speed: Unknown!
	Duplex: Unknown! (255)
$ ethtool -s eth1 speed 1000 duplex full
$ ethtool eth1
Settings for eth1:
...
	Speed: 1000Mb/s
	Duplex: Full

Based on a patch by Roopa Prabhu.
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -146,6 +146,10 @@ struct virtnet_info {
 	virtio_net_ctrl_ack ctrl_status;
 	u8 ctrl_promisc;
 	u8 ctrl_allmulti;
+
+	/* Ethtool settings */
+	u8 duplex;
+	u32 speed;
 };
 
 struct padded_vnet_hdr {
@@ -1376,6 +1380,58 @@ static void virtnet_get_channels(struct net_device *dev,
 	channels->other_count = 0;
 }
 
+/* Check if the user is trying to change anything besides speed/duplex */
+static bool virtnet_validate_ethtool_cmd(const struct ethtool_cmd *cmd)
+{
+	struct ethtool_cmd diff1 = *cmd;
+	struct ethtool_cmd diff2 = {};
+
+	/* advertising and cmd are usually set, ignore port because we set it */
+	ethtool_cmd_speed_set(&diff1, 0);
+	diff1.advertising = 0;
+	diff1.duplex = 0;
+	diff1.port = 0;
+	diff1.cmd = 0;
+
+	return !memcmp(&diff1, &diff2, sizeof(diff1));
+}
+
+static int virtnet_set_settings(struct net_device *dev, struct ethtool_cmd *cmd)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+	u32 speed;
+
+	speed = ethtool_cmd_speed(cmd);
+	/* don't allow custom speed and duplex */
+	if (!ethtool_validate_speed(speed) ||
+	    !ethtool_validate_duplex(cmd->duplex) ||
+	    !virtnet_validate_ethtool_cmd(cmd))
+		return -EINVAL;
+	vi->speed = speed;
+	vi->duplex = cmd->duplex;
+
+	return 0;
+}
+
+static int virtnet_get_settings(struct net_device *dev, struct ethtool_cmd *cmd)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+
+	ethtool_cmd_speed_set(cmd, vi->speed);
+	cmd->duplex = vi->duplex;
+	cmd->port = PORT_OTHER;
+
+	return 0;
+}
+
+static void virtnet_init_settings(struct net_device *dev)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+
+	vi->speed = SPEED_UNKNOWN;
+	vi->duplex = DUPLEX_UNKNOWN;
+}
+
 static const struct ethtool_ops virtnet_ethtool_ops = {
 	.get_drvinfo = virtnet_get_drvinfo,
 	.get_link = ethtool_op_get_link,
@@ -1383,6 +1439,8 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
 	.set_channels = virtnet_set_channels,
 	.get_channels = virtnet_get_channels,
 	.get_ts_info = ethtool_op_get_ts_info,
+	.get_settings = virtnet_get_settings,
+	.set_settings = virtnet_set_settings,
 };
 
 #define MIN_MTU 68
@@ -1855,6 +1913,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	netif_set_real_num_tx_queues(dev, vi->curr_queue_pairs);
 	netif_set_real_num_rx_queues(dev, vi->curr_queue_pairs);
 
+	virtnet_init_settings(dev);
+
 	err = register_netdev(dev);
 	if (err) {
 		pr_debug("virtio_net: registering device failed\n");