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>

3 files changed, 7 insertions, 1 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 67deae60214c..1cd6297fd34b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2413,6 +2413,7 @@ struct sk_buff *__skb_gso_segment(struct sk_buff *skb,
                         return ERR_PTR(err);
         }
 
+        SKB_GSO_CB(skb)->mac_offset = skb_headroom(skb);
         skb_reset_mac_header(skb);
         skb_reset_mac_len(skb);
 
diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index d9d55209db67..3e9b2c3e30f0 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -77,6 +77,7 @@ static const char netdev_features_strings[NETDEV_FEATURE_COUNT][ETH_GSTRING_LEN]
         [NETIF_F_TSO_ECN_BIT] =          "tx-tcp-ecn-segmentation",
         [NETIF_F_TSO6_BIT] =             "tx-tcp6-segmentation",
         [NETIF_F_FSO_BIT] =              "tx-fcoe-segmentation",
+        [NETIF_F_GSO_GRE_BIT] =          "tx-gre-segmentation",
 
         [NETIF_F_FCOE_CRC_BIT] =         "tx-checksum-fcoe-crc",
         [NETIF_F_SCTP_CSUM_BIT] =        "tx-checksum-sctp",
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6c1ad09f8796..2a3ca33c30aa 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2738,6 +2738,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
         unsigned int mss = skb_shinfo(skb)->gso_size;
         unsigned int doffset = skb->data - skb_mac_header(skb);
         unsigned int offset = doffset;
+        unsigned int tnl_hlen = skb_tnl_header_len(skb);
         unsigned int headroom;
         unsigned int len;
         int sg = !!(features & NETIF_F_SG);
@@ -2814,7 +2815,10 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
                 skb_set_network_header(nskb, skb->mac_len);
                 nskb->transport_header = (nskb->network_header +
                                           skb_network_header_len(skb));
-                skb_copy_from_linear_data(skb, nskb->data, doffset);
+
+                skb_copy_from_linear_data_offset(skb, -tnl_hlen,
+                                                 nskb->data - tnl_hlen,
+                                                 doffset + tnl_hlen);
 
                 if (fskb != skb_shinfo(skb)->frag_list)
                         continue;