[PATCH net-next 6/8] net: gre: Implement LCO for GRE over IPv4

[Edward Cree <ecree@solarflare.com>]

Signed-off-by: Edward Cree <ecree@solarflare.com>
---
 net/ipv4/ip_gre.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 04a48c0..8a589d3 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -440,6 +440,20 @@ drop:
 	return 0;
 }
 
+static __sum16 gre_checksum(struct sk_buff *skb)
+{
+	__sum16 csum;
+
+	if (skb->ip_summed == CHECKSUM_PARTIAL) {
+		csum = csum_fold(lco_csum(skb));
+		if (csum == 0)
+			csum = CSUM_MANGLED_0;
+		return csum;
+	} else {
+		return csum_fold(skb_checksum(skb, 0, skb->len, 0));
+	}
+}
+
 static void build_header(struct sk_buff *skb, int hdr_len, __be16 flags,
 			 __be16 proto, __be32 key, __be32 seq)
 {
@@ -467,8 +481,7 @@ static void build_header(struct sk_buff *skb, int hdr_len, __be16 flags,
 		    !(skb_shinfo(skb)->gso_type &
 		      (SKB_GSO_GRE | SKB_GSO_GRE_CSUM))) {
 			*ptr = 0;
-			*(__sum16 *)ptr = csum_fold(skb_checksum(skb, 0,
-								 skb->len, 0));
+			*(__sum16 *)ptr = gre_checksum(skb);
 		}
 	}
 }
@@ -493,7 +506,7 @@ static void __gre_xmit(struct sk_buff *skb, struct net_device *dev,
 static struct sk_buff *gre_handle_offloads(struct sk_buff *skb,
 					   bool csum)
 {
-	return iptunnel_handle_offloads(skb, csum,
+	return iptunnel_handle_offloads(skb, false,
 					csum ? SKB_GSO_GRE_CSUM : SKB_GSO_GRE);
 }