vlan: allow TSO setting on vlan interfaces

When we need to shape traffic using low speeds, we need to
disable tso on network interface :

ethtool -K eth0.2240 tso off

It seems vlan interfaces miss the set_tso() ethtool method.

Before enabling TSO, we must check real device supports
TSO for VLAN-tagged packets and enables TSO.

Note that a TSO change on real device propagates TSO setting
on all vlans, even if admin selected a different TSO setting.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan_dev.c

@@ -836,12 +836,32 @@ static struct rtnl_link_stats64 *vlan_dev_get_stats64(struct net_device *dev, st
 	return stats;
 }
 
+static int vlan_ethtool_set_tso(struct net_device *dev, u32 data)
+{
+       if (data) {
+		struct net_device *real_dev = vlan_dev_info(dev)->real_dev;
+
+		/* Underlying device must support TSO for VLAN-tagged packets
+		 * and must have TSO enabled now.
+		 */
+		if (!(real_dev->vlan_features & NETIF_F_TSO))
+			return -EOPNOTSUPP;
+		if (!(real_dev->features & NETIF_F_TSO))
+			return -EINVAL;
+		dev->features |= NETIF_F_TSO;
+	} else {
+		dev->features &= ~NETIF_F_TSO;
+	}
+	return 0;
+}
+
 static const struct ethtool_ops vlan_ethtool_ops = {
 	.get_settings	        = vlan_ethtool_get_settings,
 	.get_drvinfo	        = vlan_ethtool_get_drvinfo,
 	.get_link		= ethtool_op_get_link,
 	.get_rx_csum		= vlan_ethtool_get_rx_csum,
 	.get_flags		= vlan_ethtool_get_flags,
+	.set_tso                = vlan_ethtool_set_tso,
 };
 
 static const struct net_device_ops vlan_netdev_ops = {