net: local checksum offload for encapsulation
The arithmetic properties of the ones-complement checksum mean that a
correctly checksummed inner packet, including its checksum, has a ones
complement sum depending only on whatever value was used to initialise
the checksum field before checksumming (in the case of TCP and UDP,
this is the ones complement sum of the pseudo header, complemented).
Consequently, if we are going to offload the inner checksum with
CHECKSUM_PARTIAL, we can compute the outer checksum based only on the
packed data not covered by the inner checksum, and the initial value of
the inner checksum field.
Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_checksum.c b/net/ipv6/ip6_checksum.c
index 9a4d732..4924bd7 100644
--- a/net/ipv6/ip6_checksum.c
+++ b/net/ipv6/ip6_checksum.c
@@ -98,11 +98,13 @@
uh->check = 0;
else if (skb_is_gso(skb))
uh->check = ~udp_v6_check(len, saddr, daddr, 0);
- else if (skb_dst(skb) && skb_dst(skb)->dev &&
- (skb_dst(skb)->dev->features & NETIF_F_IPV6_CSUM)) {
-
- BUG_ON(skb->ip_summed == CHECKSUM_PARTIAL);
-
+ else if (skb->ip_summed == CHECKSUM_PARTIAL) {
+ uh->check = 0;
+ uh->check = udp_v6_check(len, saddr, daddr, lco_csum(skb));
+ if (uh->check == 0)
+ uh->check = CSUM_MANGLED_0;
+ } else if (skb_dst(skb) && skb_dst(skb)->dev &&
+ (skb_dst(skb)->dev->features & NETIF_F_IPV6_CSUM)) {
skb->ip_summed = CHECKSUM_PARTIAL;
skb->csum_start = skb_transport_header(skb) - skb->head;
skb->csum_offset = offsetof(struct udphdr, check);
@@ -110,8 +112,6 @@
} else {
__wsum csum;
- BUG_ON(skb->ip_summed == CHECKSUM_PARTIAL);
-
uh->check = 0;
csum = skb_checksum(skb, 0, len, 0);
uh->check = udp_v6_check(len, saddr, daddr, csum);
