/*
   * xfrm4_mode_transport.c - Transport mode encapsulation for IPv4.
   *
   * Copyright (c) 2004-2006 Herbert Xu <herbert@gondor.apana.org.au>
   */
  
  #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/ip.h>
  #include <net/xfrm.h>
  
  /* Add encapsulation header.
   *
   * The IP header will be moved forward to make space for the encapsulation
   * header.

   */

  static int xfrm4_transport_output(struct xfrm_state *x, struct sk_buff *skb)

  {

  	struct iphdr *iph = ip_hdr(skb);
  	int ihl = iph->ihl * 4;

  	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 + ihl;

  	__skb_pull(skb, ihl);

  	memmove(skb_network_header(skb), iph, ihl);

  	return 0;
  }

  /* Remove encapsulation header.
   *
   * The IP header will be moved over the top of the encapsulation header.
   *
   * On entry, skb->h shall point to where the IP header should be and skb->nh
   * shall be set to where the IP header currently is.  skb->data shall point
   * to the start of the payload.
   */

  static int xfrm4_transport_input(struct xfrm_state *x, struct sk_buff *skb)
  {

  	int ihl = skb->data - skb_transport_header(skb);

  	if (skb->transport_header != skb->network_header) {

  		memmove(skb_transport_header(skb),
  			skb_network_header(skb), ihl);

  		skb->network_header = skb->transport_header;

  	}

  	ip_hdr(skb)->tot_len = htons(skb->len + ihl);

  	skb_reset_transport_header(skb);

  	return 0;
  }
  
  static struct xfrm_mode xfrm4_transport_mode = {
  	.input = xfrm4_transport_input,
  	.output = xfrm4_transport_output,
  	.owner = THIS_MODULE,
  	.encap = XFRM_MODE_TRANSPORT,
  };
  
  static int __init xfrm4_transport_init(void)
  {
  	return xfrm_register_mode(&xfrm4_transport_mode, AF_INET);
  }
  
  static void __exit xfrm4_transport_exit(void)
  {
  	int err;
  
  	err = xfrm_unregister_mode(&xfrm4_transport_mode, AF_INET);
  	BUG_ON(err);
  }
  
  module_init(xfrm4_transport_init);
  module_exit(xfrm4_transport_exit);
  MODULE_LICENSE("GPL");
  MODULE_ALIAS_XFRM_MODE(AF_INET, XFRM_MODE_TRANSPORT);