ipip: capture inner headers during encapsulation

Allow IPIP to make use of tx-checksum offloading.
Signed-off-by: NPravin B Shelar <pshelar@nicira.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ipip.c

@@ -483,11 +483,6 @@ static netdev_tx_t ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	if (skb->protocol != htons(ETH_P_IP))
 		goto tx_error;
-
-	if (skb->ip_summed == CHECKSUM_PARTIAL &&
-	    skb_checksum_help(skb))
-		goto tx_error;
-
 	old_iph = ip_hdr(skb);
 
 	if (tos & 1)
@@ -572,6 +567,13 @@ static netdev_tx_t ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 		old_iph = ip_hdr(skb);
 	}
 
+	if (!skb->encapsulation) {
+		skb_reset_inner_headers(skb);
+		skb->encapsulation = 1;
+	}
+	if (skb->ip_summed != CHECKSUM_PARTIAL)
+		skb->ip_summed = CHECKSUM_NONE;
+
 	skb->transport_header = skb->network_header;
 	skb_push(skb, sizeof(struct iphdr));
 	skb_reset_network_header(skb);
@@ -599,7 +601,6 @@ static netdev_tx_t ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 		iph->ttl	=	old_iph->ttl;
 
 	nf_reset(skb);
-	skb->ip_summed = CHECKSUM_NONE;
 
 	pkt_len = skb->len - skb_transport_offset(skb);
 	err = ip_local_out(skb);