/*
 * xfrm4_mode_tunnel.c - Tunnel mode encapsulation for IPv4.
 *
 * Copyright (c) 2004-2006 Herbert Xu <herbert@gondor.apana.org.au>
 */

#include <linux/gfp.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/stringify.h>
#include <net/dst.h>
#include <net/inet_ecn.h>
#include <net/ip.h>
#include <net/xfrm.h>

/* Add encapsulation header.
 *
 * The top IP header will be constructed per RFC 2401.
 */
static int xfrm4_mode_tunnel_output(struct xfrm_state *x, struct sk_buff *skb)
{
	struct dst_entry *dst = skb_dst(skb);
	struct iphdr *top_iph;
	int flags;

	skb_set_inner_network_header(skb, skb_network_offset(skb));
	skb_set_inner_transport_header(skb, skb_transport_offset(skb));

	skb_set_network_header(skb, -x->props.header_len);
	skb->mac_header = skb->network_header +
			  offsetof(struct iphdr, protocol);
	skb->transport_header = skb->network_header + sizeof(*top_iph);
	top_iph = ip_hdr(skb);

	top_iph->ihl = 5;
	top_iph->version = 4;

	top_iph->protocol = xfrm_af2proto(skb_dst(skb)->ops->family);

	/* DS disclosing depends on XFRM_SA_XFLAG_DONT_ENCAP_DSCP */
	if (x->props.extra_flags & XFRM_SA_XFLAG_DONT_ENCAP_DSCP)
		top_iph->tos = 0;
	else
		top_iph->tos = XFRM_MODE_SKB_CB(skb)->tos;
	top_iph->tos = INET_ECN_encapsulate(top_iph->tos,
					    XFRM_MODE_SKB_CB(skb)->tos);

	flags = x->props.flags;
	if (flags & XFRM_STATE_NOECN)
		IP_ECN_clear(top_iph);

	top_iph->frag_off = (flags & XFRM_STATE_NOPMTUDISC) ?
		0 : (XFRM_MODE_SKB_CB(skb)->frag_off & htons(IP_DF));

	top_iph->ttl = ip4_dst_hoplimit(xfrm_dst_child(dst));

	top_iph->saddr = x->props.saddr.a4;
	top_iph->daddr = x->id.daddr.a4;
	ip_select_ident(dev_net(dst->dev), skb, NULL);

	return 0;
}

static struct xfrm_mode xfrm4_tunnel_mode = {
	.output2 = xfrm4_mode_tunnel_output,
	.owner = THIS_MODULE,
	.encap = XFRM_MODE_TUNNEL,
	.flags = XFRM_MODE_FLAG_TUNNEL,
	.family = AF_INET,
};

static int __init xfrm4_mode_tunnel_init(void)
{
	return xfrm_register_mode(&xfrm4_tunnel_mode);
}

static void __exit xfrm4_mode_tunnel_exit(void)
{
	xfrm_unregister_mode(&xfrm4_tunnel_mode);
}

module_init(xfrm4_mode_tunnel_init);
module_exit(xfrm4_mode_tunnel_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS_XFRM_MODE(AF_INET, XFRM_MODE_TUNNEL);