1. 根目录:
2. net
3. ipv6
4. udp_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.
 *
 *      UDPv6 GSO support
 */
#include <linux/skbuff.h>
#include <net/protocol.h>
#include <net/ipv6.h>
#include <net/udp.h>
#include <net/ip6_checksum.h>
#include "ip6_offload.h"

static int udp6_ufo_send_check(struct sk_buff *skb)
{
	const struct ipv6hdr *ipv6h;
	struct udphdr *uh;

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

	if (likely(!skb->encapsulation)) {
		ipv6h = ipv6_hdr(skb);
		uh = udp_hdr(skb);

		uh->check = ~csum_ipv6_magic(&ipv6h->saddr, &ipv6h->daddr, skb->len,
					     IPPROTO_UDP, 0);
		skb->csum_start = skb_transport_header(skb) - skb->head;
		skb->csum_offset = offsetof(struct udphdr, check);
		skb->ip_summed = CHECKSUM_PARTIAL;
	}

	return 0;
}

static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
					 netdev_features_t features)
{
	struct sk_buff *segs = ERR_PTR(-EINVAL);
	unsigned int mss;
	unsigned int unfrag_ip6hlen, unfrag_len;
	struct frag_hdr *fptr;
	u8 *packet_start, *prevhdr;
	u8 nexthdr;
	u8 frag_hdr_sz = sizeof(struct frag_hdr);
	int offset;
	__wsum csum;
	int tnl_hlen;

	mss = skb_shinfo(skb)->gso_size;
	if (unlikely(skb->len <= mss))
		goto out;

	if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) {
		/* Packet is from an untrusted source, reset gso_segs. */
		int type = skb_shinfo(skb)->gso_type;

		if (unlikely(type & ~(SKB_GSO_UDP |
				      SKB_GSO_DODGY |
				      SKB_GSO_UDP_TUNNEL |
				      SKB_GSO_GRE |
				      SKB_GSO_IPIP |
				      SKB_GSO_SIT |
				      SKB_GSO_MPLS) ||
			     !(type & (SKB_GSO_UDP))))
			goto out;

		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss);

		segs = NULL;
		goto out;
	}

	if (skb->encapsulation && skb_shinfo(skb)->gso_type & SKB_GSO_UDP_TUNNEL)
		segs = skb_udp_tunnel_segment(skb, features);
	else {
		/* Do software UFO. Complete and fill in the UDP checksum as HW cannot
		 * do checksum of UDP packets sent as multiple IP fragments.
		 */
		offset = skb_checksum_start_offset(skb);
		csum = skb_checksum(skb, offset, skb->len - offset, 0);
		offset += skb->csum_offset;
		*(__sum16 *)(skb->data + offset) = csum_fold(csum);
		skb->ip_summed = CHECKSUM_NONE;

		/* Check if there is enough headroom to insert fragment header. */
		tnl_hlen = skb_tnl_header_len(skb);
		if (skb->mac_header < (tnl_hlen + frag_hdr_sz)) {
			if (gso_pskb_expand_head(skb, tnl_hlen + frag_hdr_sz))
				goto out;
		}

		/* Find the unfragmentable header and shift it left by frag_hdr_sz
		 * bytes to insert fragment header.
		 */
		unfrag_ip6hlen = ip6_find_1stfragopt(skb, &prevhdr);
		nexthdr = *prevhdr;
		*prevhdr = NEXTHDR_FRAGMENT;
		unfrag_len = (skb_network_header(skb) - skb_mac_header(skb)) +
			     unfrag_ip6hlen + tnl_hlen;
		packet_start = (u8 *) skb->head + SKB_GSO_CB(skb)->mac_offset;
		memmove(packet_start-frag_hdr_sz, packet_start, unfrag_len);

		SKB_GSO_CB(skb)->mac_offset -= frag_hdr_sz;
		skb->mac_header -= frag_hdr_sz;
		skb->network_header -= frag_hdr_sz;

		fptr = (struct frag_hdr *)(skb_network_header(skb) + unfrag_ip6hlen);
		fptr->nexthdr = nexthdr;
		fptr->reserved = 0;
		fptr->identification = skb_shinfo(skb)->ip6_frag_id;

		/* Fragment the skb. ipv6 header and the remaining fields of the
		 * fragment header are updated in ipv6_gso_segment()
		 */
		segs = skb_segment(skb, features);
	}

out:
	return segs;
}
static const struct net_offload udpv6_offload = {
	.callbacks = {
		.gso_send_check =	udp6_ufo_send_check,
		.gso_segment	=	udp6_ufo_fragment,
	},
};

int __init udp_offload_init(void)
{
	return inet6_add_offload(&udpv6_offload, IPPROTO_UDP);
}