[PATCH 4.4 19/75] vxlan: Relax MTU constraints

Greg Kroah-Hartman
2016-06-22T23:19:59Z

From: David Wragg <david@weave.works>

[ Upstream commit 72564b59ffc438ea103b0727a921aaddce766728 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/vxlan.c | 36 +++++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 11 deletions(-)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -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)