1. 根目录:
2. net
3. ipv6
4. tcpv6_offload.c

/*
 *	IPV6 GSO/GRO offload support
 *	Linux INET6 implementation
 *
 *	This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 *
 *      TCPv6 GSO/GRO support
 */
#include <linux/skbuff.h>
#include <net/protocol.h>
#include <net/tcp.h>
#include <net/ip6_checksum.h>
#include "ip6_offload.h"

static int tcp_v6_gso_send_check(struct sk_buff *skb)
{
	const struct ipv6hdr *ipv6h;
	struct tcphdr *th;

	if (!pskb_may_pull(skb, sizeof(*th)))
		return -EINVAL;

	ipv6h = ipv6_hdr(skb);
	th = tcp_hdr(skb);

	th->check = 0;
	skb->ip_summed = CHECKSUM_PARTIAL;
	__tcp_v6_send_check(skb, &ipv6h->saddr, &ipv6h->daddr);
	return 0;
}

static struct sk_buff **tcp6_gro_receive(struct sk_buff **head,
					 struct sk_buff *skb)
{
	const struct ipv6hdr *iph = skb_gro_network_header(skb);
	__wsum wsum;

	/* Don't bother verifying checksum if we're going to flush anyway. */
	if (NAPI_GRO_CB(skb)->flush)
		goto skip_csum;

	wsum = skb->csum;

	switch (skb->ip_summed) {
	case CHECKSUM_NONE:
		wsum = skb_checksum(skb, skb_gro_offset(skb), skb_gro_len(skb),
				    wsum);

		/* fall through */

	case CHECKSUM_COMPLETE:
		if (!tcp_v6_check(skb_gro_len(skb), &iph->saddr, &iph->daddr,
				  wsum)) {
			skb->ip_summed = CHECKSUM_UNNECESSARY;
			break;
		}

		NAPI_GRO_CB(skb)->flush = 1;
		return NULL;
	}

skip_csum:
	return tcp_gro_receive(head, skb);
}

static int tcp6_gro_complete(struct sk_buff *skb, int thoff)
{
	const struct ipv6hdr *iph = ipv6_hdr(skb);
	struct tcphdr *th = tcp_hdr(skb);

	th->check = ~tcp_v6_check(skb->len - thoff, &iph->saddr,
				  &iph->daddr, 0);
	skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;

	return tcp_gro_complete(skb);
}

static const struct net_offload tcpv6_offload = {
	.callbacks = {
		.gso_send_check	=	tcp_v6_gso_send_check,
		.gso_segment	=	tcp_gso_segment,
		.gro_receive	=	tcp6_gro_receive,
		.gro_complete	=	tcp6_gro_complete,
	},
};

int __init tcpv6_offload_init(void)
{
	return inet6_add_offload(&tcpv6_offload, IPPROTO_TCP);
}