[PATCH 4.4 20/75] geneve: Relax MTU constraints

Greg Kroah-Hartman
2016-06-22T23:19:58Z

From: David Wragg <david@weave.works>

[ Upstream commit 55e5bfb53cff286c1c1ff49f51325dc15c7fea63 ]

Allow the MTU of geneve devices to be set to large values, in order to
exploit underlying networks with larger frame sizes.

GENEVE does not have a fixed encapsulation overhead (an openvswitch
rule can add variable length options), so there is no relevant maximum
MTU to enforce. A maximum of IP_MAX_MTU is used instead.
Encapsulated packets that are too big for the underlying network will
get dropped on the floor.

Signed-off-by: David Wragg <david@weave.works>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/geneve.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -994,6 +994,17 @@ static netdev_tx_t geneve_xmit(struct sk
return geneve_xmit_skb(skb, dev, info);
}

+static int geneve_change_mtu(struct net_device *dev, int new_mtu)
+{
+ /* GENEVE overhead is not fixed, so we can't enforce a more
+ * precise max MTU.
+ */
+ if (new_mtu < 68 || new_mtu > IP_MAX_MTU)
+ return -EINVAL;
+ dev->mtu = new_mtu;
+ return 0;
+}
+
static int geneve_fill_metadata_dst(struct net_device *dev, struct sk_buff *skb)
{
struct ip_tunnel_info *info = skb_tunnel_info(skb);
@@ -1038,7 +1049,7 @@ static const struct net_device_ops genev
.ndo_stop = geneve_stop,
.ndo_start_xmit = geneve_xmit,
.ndo_get_stats64 = ip_tunnel_get_stats64,
- .ndo_change_mtu = eth_change_mtu,
+ .ndo_change_mtu = geneve_change_mtu,
.ndo_validate_addr = eth_validate_addr,
.ndo_set_mac_address = eth_mac_addr,
.ndo_fill_metadata_dst = geneve_fill_metadata_dst,