tcp: gro: add checksuming helpers

skb with CHECKSUM_NONE cant currently be handled by GRO, and
we notice this deep in GRO stack in tcp[46]_gro_receive()

But there are cases where GRO can be a benefit, even with a lack
of checksums.

This preliminary work is needed to add GRO support
to tunnels.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 3 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 385eb79cf6aa..75735c9a6a9d 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2803,6 +2803,8 @@ void tcp4_proc_exit(void)
 struct sk_buff **tcp4_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 {
         const struct iphdr *iph = skb_gro_network_header(skb);
+        __wsum wsum;
+        __sum16 sum;
 
         switch (skb->ip_summed) {
         case CHECKSUM_COMPLETE:
@@ -2811,11 +2813,22 @@ struct sk_buff **tcp4_gro_receive(struct sk_buff **head, struct sk_buff *skb)
                         skb->ip_summed = CHECKSUM_UNNECESSARY;
                         break;
                 }
-
-                /* fall through */
-        case CHECKSUM_NONE:
+flush:
                 NAPI_GRO_CB(skb)->flush = 1;
                 return NULL;
+
+        case CHECKSUM_NONE:
+                wsum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
+                                          skb_gro_len(skb), IPPROTO_TCP, 0);
+                sum = csum_fold(skb_checksum(skb,
+                                             skb_gro_offset(skb),
+                                             skb_gro_len(skb),
+                                             wsum));
+                if (sum)
+                        goto flush;
+
+                skb->ip_summed = CHECKSUM_UNNECESSARY;
+                break;
         }
 
         return tcp_gro_receive(head, skb);