vxlan: Relax MTU constraints

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 <david@weave.works>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 6543918..e992c6a 100644 (file)
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2367,29 +2367,43 @@ static void vxlan_set_multicast_list(struct net_device *dev)
 {
 }
 
-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)