Allow ethtool to change tun link settings

Let user space set whatever it would like to advertise for the
tun interface.  Preserve the existing defaults.
Signed-off-by: Chas Williams <3chas3@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -81,6 +81,9 @@
 #include <linux/uaccess.h>
 #include <linux/proc_fs.h>
 
+static void tun_default_link_ksettings(struct net_device *dev,
+				       struct ethtool_link_ksettings *cmd);
+
 /* Uncomment to enable debugging */
 /* #define TUN_DEBUG 1 */
 
@@ -242,6 +245,7 @@ struct tun_struct {
 	struct bpf_prog __rcu *xdp_prog;
 	struct tun_prog __rcu *steering_prog;
 	struct tun_prog __rcu *filter_prog;
+	struct ethtool_link_ksettings link_ksettings;
 };
 
 struct veth {
@@ -2295,6 +2299,7 @@ static void tun_setup(struct net_device *dev)
 
 	tun->owner = INVALID_UID;
 	tun->group = INVALID_GID;
+	tun_default_link_ksettings(dev, &tun->link_ksettings);
 
 	dev->ethtool_ops = &tun_ethtool_ops;
 	dev->needs_free_netdev = true;
@@ -3326,7 +3331,7 @@ static struct miscdevice tun_miscdev = {
 
 /* ethtool interface */
 
-static int tun_get_link_ksettings(struct net_device *dev,
+static void tun_default_link_ksettings(struct net_device *dev,
 				       struct ethtool_link_ksettings *cmd)
 {
 	ethtool_link_ksettings_zero_link_mode(cmd, supported);
@@ -3336,6 +3341,23 @@ static int tun_get_link_ksettings(struct net_device *dev,
 	cmd->base.port		= PORT_TP;
 	cmd->base.phy_address	= 0;
 	cmd->base.autoneg	= AUTONEG_DISABLE;
+}
+
+static int tun_get_link_ksettings(struct net_device *dev,
+				  struct ethtool_link_ksettings *cmd)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+
+	memcpy(cmd, &tun->link_ksettings, sizeof(*cmd));
+	return 0;
+}
+
+static int tun_set_link_ksettings(struct net_device *dev,
+				  const struct ethtool_link_ksettings *cmd)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+
+	memcpy(&tun->link_ksettings, cmd, sizeof(*cmd));
 	return 0;
 }
 
@@ -3406,6 +3428,7 @@ static const struct ethtool_ops tun_ethtool_ops = {
 	.get_coalesce   = tun_get_coalesce,
 	.set_coalesce   = tun_set_coalesce,
 	.get_link_ksettings = tun_get_link_ksettings,
+	.set_link_ksettings = tun_set_link_ksettings,
 };
 
 static int tun_queue_resize(struct tun_struct *tun)