net: provide a default dev->ethtool_ops

Instead of forcing device drivers to provide empty ethtool_ops or tweak
net/core/ethtool.c again, we could provide a generic ethtool_ops.

This occurred to me when I wanted to add GSO support to GRE tunnels.
ethtool -k support should be generic for all drivers.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Maciej Żenczykowski <maze@google.com>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -5974,6 +5974,8 @@ struct netdev_queue *dev_ingress_queue_create(struct net_device *dev)
 	return queue;
 }
 
+static const struct ethtool_ops default_ethtool_ops;
+
 /**
  *	alloc_netdev_mqs - allocate network device
  *	@sizeof_priv:	size of private data to allocate space for
@@ -6061,6 +6063,8 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 
 	strcpy(dev->name, name);
 	dev->group = INIT_NETDEV_GROUP;
+	if (!dev->ethtool_ops)
+		dev->ethtool_ops = &default_ethtool_ops;
 	return dev;
 
 free_all:

net/core/ethtool.c

@@ -1426,18 +1426,6 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
 	if (copy_from_user(&ethcmd, useraddr, sizeof(ethcmd)))
 		return -EFAULT;
 
-	if (!dev->ethtool_ops) {
-		/* A few commands do not require any driver support,
-		 * are unprivileged, and do not change anything, so we
-		 * can take a shortcut to them. */
-		if (ethcmd == ETHTOOL_GDRVINFO)
-			return ethtool_get_drvinfo(dev, useraddr);
-		else if (ethcmd == ETHTOOL_GET_TS_INFO)
-			return ethtool_get_ts_info(dev, useraddr);
-		else
-			return -EOPNOTSUPP;
-	}
-
 	/* Allow some commands to be done by anyone */
 	switch (ethcmd) {
 	case ETHTOOL_GSET: