netlink: add support for NIC driver ioctls

By returning -ENOIOCTLCMD, sock_do_ioctl() falls back to calling
dev_ioctl(), which provides support for NIC driver ioctls, which
includes ethtool support. This is similar to the way ioctls are handled
in udp.c or tcp.c.

This removes the requirement that ethtool for example be tied to the
support of a specific L3 protocol (ethtool uses an AF_INET socket
today).
Signed-off-by: NDavid Decotigny <decot@googlers.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -1033,6 +1033,14 @@ static int netlink_getname(struct socket *sock, struct sockaddr *addr,
 	return 0;
 }
 
+static int netlink_ioctl(struct socket *sock, unsigned int cmd,
+			 unsigned long arg)
+{
+	/* try to hand this ioctl down to the NIC drivers.
+	 */
+	return -ENOIOCTLCMD;
+}
+
 static struct sock *netlink_getsockbyportid(struct sock *ssk, u32 portid)
 {
 	struct sock *sock;
@@ -2494,7 +2502,7 @@ static const struct proto_ops netlink_ops = {
 	.accept =	sock_no_accept,
 	.getname =	netlink_getname,
 	.poll =		datagram_poll,
-	.ioctl =	sock_no_ioctl,
+	.ioctl =	netlink_ioctl,
 	.listen =	sock_no_listen,
 	.shutdown =	sock_no_shutdown,
 	.setsockopt =	netlink_setsockopt,