v4 GRE: Add TCP segmentation offload for GRE

Following patch adds GRE protocol offload handler so that
skb_gso_segment() can segment GRE packets.
SKB GSO CB is added to keep track of total header length so that
skb_segment can push entire header. e.g. in case of GRE, skb_segment
need to push inner and outer headers to every segment.
New NETIF_F_GRE_GSO feature is added for devices which support HW
GRE TSO offload. Currently none of devices support it therefore GRE GSO
always fall backs to software GSO.

[ Compute pkt_len before ip_local_out() invocation. -DaveM ]

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 3 insertions, 1 deletions

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index f26f0da7f095..8234c1dcdf72 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -99,6 +99,7 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
                      ~(SKB_GSO_UDP |
                        SKB_GSO_DODGY |
                        SKB_GSO_TCP_ECN |
+                       SKB_GSO_GRE |
                        SKB_GSO_TCPV6 |
                        0)))
                 goto out;
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index 0c8934a317c2..cf05cf073c51 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -56,7 +56,8 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
                 /* Packet is from an untrusted source, reset gso_segs. */
                 int type = skb_shinfo(skb)->gso_type;
 
-                if (unlikely(type & ~(SKB_GSO_UDP | SKB_GSO_DODGY) ||
+                if (unlikely(type & ~(SKB_GSO_UDP | SKB_GSO_DODGY |
+                                      SKB_GSO_GRE) ||
                              !(type & (SKB_GSO_UDP))))
                         goto out;