/*
 * icmp_error.c
 *
 * cc -D__KERNEL__ -DMODULE -DCONFIG_NETFILTER * -I/usr/src/linux/include -O -Wall -g -D__SMP__ -DSMP -c * icmp_error.c -o icmp_error.o
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <asm/uaccess.h> /* copy_from_user() */
#include <net/checksum.h> 
#include <asm/checksum.h>  /* ip_compute_csum() */
#include <linux/net.h>
#include <linux/ip.h>
#include <linux/in.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/skbuff.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/locks.h>
#include <linux/icmp.h>

#define	MODULE_NAME "icmp_error"
#define	MODULE_VERSION "0.1"

/* print line of info */
#define linfo(fmt, args...)	printk(KERN_INFO MODULE_NAME ": " fmt "\n", ## args)
/* print info msgs */
#define binfo(fmt, args...)	printk(KERN_INFO MODULE_NAME ": " fmt, ## args)
/* print info msg */
#define info(fmt, args...)	printk(fmt, ## args)

/*
 * this function is called when packets enter the postrouting 
 * (packets about to hit wire)
 */
static unsigned int hook_post_routing(unsigned int hook,
           			struct sk_buff **skb,
           			const struct net_device *indev,
           			const struct net_device *outdev,
           			int (*okfn)(struct sk_buff *))
{
	struct iphdr *iph = (*skb)->nh.iph;
	unsigned char *type;

	MOD_INC_USE_COUNT;

	/*
	 * check for ICMP packets, ignore all others
	 */
	if (iph->protocol != IPPROTO_ICMP) 
		goto out;


        binfo("pr: ");

        if ((*skb)->h.icmph->type == ICMP_ECHO) {
		info("ICMP_ECHO ");	
	} else if ((*skb)->h.icmph->type == ICMP_ECHOREPLY) {
		info("ICMP_ECHOREPLY ");	
	} else {
                /* goto out; */
		;
	}

	type = (*skb)->nh.raw;
	type += 20; /* assume iphdr is 20 bytes, no options */

	info("manual icmp type offset gives: %u ", *type);

out:
	info("\n");
	MOD_DEC_USE_COUNT;

	return NF_ACCEPT;
}

/*
 * the hook operations structure
 * fed to netfilter during initialization
 */
static struct nf_hook_ops icmp_mon_post_routing_ops
= { { NULL, NULL }, hook_post_routing, PF_INET, NF_IP_POST_ROUTING, 0 };
/* = { { NULL, NULL }, hook_post_routing, PF_INET, NF_IP_LOCAL_OUT, 0 }; */
/* = { { NULL, NULL }, hook_post_routing, PF_INET, NF_IP_LOCAL_IN, 0 }; */

static int __init init(void)
{
	/*
	 * create and register the post routing hook
	 */
	if (nf_register_hook(&icmp_mon_post_routing_ops) != 0) {
		linfo("unable to register post routing hooks");
		return -ENOMEM;
	}
	
	linfo("%s version %s loaded", MODULE_NAME, MODULE_VERSION);
	return 0;
}

static void __exit fini(void)
{
	/*
	 * remove the netfilter hooks
	 */
	nf_unregister_hook(&icmp_mon_post_routing_ops);
	linfo("%s version %s unloaded", MODULE_NAME, MODULE_VERSION);
}

module_init(init);
module_exit(fini);

MODULE_AUTHOR("Ola Nordstrom <ola@triblock.com>");
MODULE_DESCRIPTION("FOO");
MODULE_LICENSE("GPL");

EXPORT_NO_SYMBOLS;