net: core: add function for incremental IPv6 pseudo header checksum updates

Add inet_proto_csum_replace16 for incrementally updating IPv6 pseudo header
checksums for IPv6 NAT.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: David S. Miller <davem@davemloft.net>

include/net/checksum.h

@@ -109,6 +109,9 @@ static inline void csum_replace2(__sum16 *sum, __be16 from, __be16 to)
 struct sk_buff;
 extern void inet_proto_csum_replace4(__sum16 *sum, struct sk_buff *skb,
 				     __be32 from, __be32 to, int pseudohdr);
+extern void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb,
+				      const __be32 *from, const __be32 *to,
+				      int pseudohdr);
 
 static inline void inet_proto_csum_replace2(__sum16 *sum, struct sk_buff *skb,
 					    __be16 from, __be16 to,

net/core/utils.c

@@ -294,6 +294,26 @@ void inet_proto_csum_replace4(__sum16 *sum, struct sk_buff *skb,
 }
 EXPORT_SYMBOL(inet_proto_csum_replace4);
 
+void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb,
+			       const __be32 *from, const __be32 *to,
+			       int pseudohdr)
+{
+	__be32 diff[] = {
+		~from[0], ~from[1], ~from[2], ~from[3],
+		to[0], to[1], to[2], to[3],
+	};
+	if (skb->ip_summed != CHECKSUM_PARTIAL) {
+		*sum = csum_fold(csum_partial(diff, sizeof(diff),
+				 ~csum_unfold(*sum)));
+		if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr)
+			skb->csum = ~csum_partial(diff, sizeof(diff),
+						  ~skb->csum);
+	} else if (pseudohdr)
+		*sum = ~csum_fold(csum_partial(diff, sizeof(diff),
+				  csum_unfold(*sum)));
+}
+EXPORT_SYMBOL(inet_proto_csum_replace16);
+
 int mac_pton(const char *s, u8 *mac)
 {
 	int i;