/*
   * 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>
  
  static inline void ipip_ecn_decapsulate(struct sk_buff *skb)
  {

  	struct iphdr *inner_iph = ipip_hdr(skb);

  	if (INET_ECN_is_ce(XFRM_MODE_SKB_CB(skb)->tos))

  		IP_ECN_set_ce(inner_iph);
  }
  
  /* 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_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 disclosed */

  	top_iph->tos = INET_ECN_encapsulate(XFRM_MODE_SKB_CB(skb)->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));

  	ip_select_ident(top_iph, dst->child, NULL);

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

  
  	top_iph->saddr = x->props.saddr.a4;
  	top_iph->daddr = x->id.daddr.a4;

  	return 0;
  }

  static int xfrm4_mode_tunnel_input(struct xfrm_state *x, struct sk_buff *skb)

  {

  	const unsigned char *old_mac;

  	int err = -EINVAL;

  	if (XFRM_MODE_SKB_CB(skb)->protocol != IPPROTO_IPIP)
  		goto out;

  	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
  		goto out;
  
  	if (skb_cloned(skb) &&
  	    (err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
  		goto out;

  	if (x->props.flags & XFRM_STATE_DECAP_DSCP)
  		ipv4_copy_dscp(XFRM_MODE_SKB_CB(skb)->tos, ipip_hdr(skb));
  	if (!(x->props.flags & XFRM_STATE_NOECN))
  		ipip_ecn_decapsulate(skb);

  	old_mac = skb_mac_header(skb);

  	skb_set_mac_header(skb, -skb->mac_len);

  	memmove(skb_mac_header(skb), old_mac, skb->mac_len);

  	skb_reset_network_header(skb);

  	err = 0;
  
  out:
  	return err;
  }
  
  static struct xfrm_mode xfrm4_tunnel_mode = {

  	.input2 = xfrm4_mode_tunnel_input,

  	.input = xfrm_prepare_input,

  	.output2 = xfrm4_mode_tunnel_output,

  	.output = xfrm4_prepare_output,

  	.owner = THIS_MODULE,
  	.encap = XFRM_MODE_TUNNEL,

  	.flags = XFRM_MODE_FLAG_TUNNEL,

  };

  static int __init xfrm4_mode_tunnel_init(void)

  {
  	return xfrm_register_mode(&xfrm4_tunnel_mode, AF_INET);
  }

  static void __exit xfrm4_mode_tunnel_exit(void)

  {
  	int err;
  
  	err = xfrm_unregister_mode(&xfrm4_tunnel_mode, AF_INET);
  	BUG_ON(err);
  }

  module_init(xfrm4_mode_tunnel_init);
  module_exit(xfrm4_mode_tunnel_exit);

  MODULE_LICENSE("GPL");
  MODULE_ALIAS_XFRM_MODE(AF_INET, XFRM_MODE_TUNNEL);