1. 根目录:
2. net
3. ipv6
4. ip6_checksum.c

#include <net/ip.h>
#include <net/udp.h>
#include <net/udplite.h>
#include <asm/checksum.h>

#ifndef _HAVE_ARCH_IPV6_CSUM
__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
			const struct in6_addr *daddr,
			__u32 len, unsigned short proto,
			__wsum csum)
{

	int carry;
	__u32 ulen;
	__u32 uproto;
	__u32 sum = (__force u32)csum;

	sum += (__force u32)saddr->s6_addr32[0];
	carry = (sum < (__force u32)saddr->s6_addr32[0]);
	sum += carry;

	sum += (__force u32)saddr->s6_addr32[1];
	carry = (sum < (__force u32)saddr->s6_addr32[1]);
	sum += carry;

	sum += (__force u32)saddr->s6_addr32[2];
	carry = (sum < (__force u32)saddr->s6_addr32[2]);
	sum += carry;

	sum += (__force u32)saddr->s6_addr32[3];
	carry = (sum < (__force u32)saddr->s6_addr32[3]);
	sum += carry;

	sum += (__force u32)daddr->s6_addr32[0];
	carry = (sum < (__force u32)daddr->s6_addr32[0]);
	sum += carry;

	sum += (__force u32)daddr->s6_addr32[1];
	carry = (sum < (__force u32)daddr->s6_addr32[1]);
	sum += carry;

	sum += (__force u32)daddr->s6_addr32[2];
	carry = (sum < (__force u32)daddr->s6_addr32[2]);
	sum += carry;

	sum += (__force u32)daddr->s6_addr32[3];
	carry = (sum < (__force u32)daddr->s6_addr32[3]);
	sum += carry;

	ulen = (__force u32)htonl((__u32) len);
	sum += ulen;
	carry = (sum < ulen);
	sum += carry;

	uproto = (__force u32)htonl(proto);
	sum += uproto;
	carry = (sum < uproto);
	sum += carry;

	return csum_fold((__force __wsum)sum);
}
EXPORT_SYMBOL(csum_ipv6_magic);
#endif

int udp6_csum_init(struct sk_buff *skb, struct udphdr *uh, int proto)
{
	int err;

	UDP_SKB_CB(skb)->partial_cov = 0;
	UDP_SKB_CB(skb)->cscov = skb->len;

	if (proto == IPPROTO_UDPLITE) {
		err = udplite_checksum_init(skb, uh);
		if (err)
			return err;
	}

	if (uh->check == 0) {
		/* RFC 2460 section 8.1 says that we SHOULD log
		   this error. Well, it is reasonable.
		 */
		LIMIT_NETDEBUG(KERN_INFO "IPv6: udp checksum is 0\n");
		return 1;
	}
	if (skb->ip_summed == CHECKSUM_COMPLETE &&
	    !csum_ipv6_magic(&ipv6_hdr(skb)->saddr, &ipv6_hdr(skb)->daddr,
			     skb->len, proto, skb->csum))
		skb->ip_summed = CHECKSUM_UNNECESSARY;

	if (!skb_csum_unnecessary(skb))
		skb->csum = ~csum_unfold(csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
							 &ipv6_hdr(skb)->daddr,
							 skb->len, proto, 0));

	return 0;
}
EXPORT_SYMBOL(udp6_csum_init);