Allow the MTU of vxlan devices without an underlying device to be set to larger values (up to a maximum based on IP packet limits and vxlan overhead).

Previously, their MTUs could not be set to higher than the conventional ethernet value of 1500. This is a very arbitrary value in the context of vxlan, and prevented vxlan devices from being able to take advantage of jumbo frames etc.

The default MTU remains 1500, for compatibility.

Signed-off-by David Wragg <[email protected]>

Acked-by Roopa Prabhu <[email protected]>

Signed-off-by David S. Miller <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 drivers/net/vxlan.c |   36 +++++++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 11 deletions(-)

drivers/net/vxlan.c +25 ~~-11~~

@@ -2364,29 +2364,43 @@ static void vxlan_set_multicast_list(str
 {
 }
 
-static int vxlan_change_mtu(struct net_device *dev, int new_mtu)
+static int __vxlan_change_mtu(struct net_device *dev,
+			      struct net_device *lowerdev,
+			      struct vxlan_rdst *dst, int new_mtu, bool strict)
 {
-	struct vxlan_dev *vxlan = netdev_priv(dev);
-	struct vxlan_rdst *dst = &vxlan->default_dst;
-	struct net_device *lowerdev;
-	int max_mtu;
+	int max_mtu = IP_MAX_MTU;
 
-	lowerdev = __dev_get_by_index(vxlan->net, dst->remote_ifindex);
-	if (lowerdev == NULL)
-		return eth_change_mtu(dev, new_mtu);
+	if (lowerdev)
+		max_mtu = lowerdev->mtu;
 
 	if (dst->remote_ip.sa.sa_family == AF_INET6)
-		max_mtu = lowerdev->mtu - VXLAN6_HEADROOM;
+		max_mtu -= VXLAN6_HEADROOM;
 	else
-		max_mtu = lowerdev->mtu - VXLAN_HEADROOM;
+		max_mtu -= VXLAN_HEADROOM;
 
-	if (new_mtu < 68 || new_mtu > max_mtu)
+	if (new_mtu < 68)
 		return -EINVAL;
 
+	if (new_mtu > max_mtu) {
+		if (strict)
+			return -EINVAL;
+
+		new_mtu = max_mtu;
+	}
+
 	dev->mtu = new_mtu;
 	return 0;
 }
 
+static int vxlan_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct vxlan_dev *vxlan = netdev_priv(dev);
+	struct vxlan_rdst *dst = &vxlan->default_dst;
+	struct net_device *lowerdev = __dev_get_by_index(vxlan->net,
+							 dst->remote_ifindex);
+	return __vxlan_change_mtu(dev, lowerdev, dst, new_mtu, true);
+}
+
 static int egress_ipv4_tun_info(struct net_device *dev, struct sk_buff *skb,
 				struct ip_tunnel_info *info,
 				__be16 sport, __be16 dport)

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/geneve-relax-mtu-constraints.patch queue-4.4/vxlan-relax-mtu-constraints.patch queue-4.4/vxlan-gre-geneve-set-a-large-mtu-on-ovs-created-tunnel-devices.patch