Problem with kernel modules

[cranium2003 <cranium2003@xxxxxxxxx>]

Hello,
  I have written a kernel module that accesses skbuff
and depending on whether packet is icmp or not it
prints IP checksum and ICMP checksum. But I am getting

sum.c: In function `hook_func1':
sum.c:24: dereferencing pointer to incomplete type
sum.c: In function `hook_func2':
sum.c:40: dereferencing pointer to incomplete type
  Whats wrong?
regards,
cranium.

*************************************************

#define __KERNEL__
#define MODULE

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>

static struct nf_hook_ops nfho1,nfho2;

unsigned int hook_func1(unsigned int hooknum,struct
sk_buff **skb,
			const struct net_device *in,
			const struct net_device *out,
			int (*okfn)(struct sk_buff *))
{
  struct sk_buff *sb = *skb;

      if(sb->nh.iph->protocol==1)
	{
	printk(KERN_DEBUG"ICMP packet\n");
	printk(KERN_DEBUG "ICMP cksum=%d,& IP
cksum=%d\n",sb->h.icmph->checksum,sb->nh.iph->check);
	}

	return NF_ACCEPT;
}


unsigned int hook_func2(unsigned int hooknum,struct
sk_buff **skb,
			const struct net_device *in,
			const struct net_device *out,
			int (*okfn)(struct sk_buff *))
{
struct sk_buff *sb = *skb;
if(sb->nh.iph->protocol==1)
{
printk(KERN_DEBUG"ICMP packet\n");
printk(KERN_DEBUG "ICMP cksum=%d,& IP
cksum=%d\n",sb->h.icmph->checksum,sb->nh.iph->check);
}
     return NF_ACCEPT;
}

static int __init init(void)
{
  nfho1.hook     = hook_func1;
  nfho1.hooknum  = NF_IP_POST_ROUTING;
  nfho1.pf       = PF_INET;
  nfho1.priority = NF_IP_PRI_FIRST;
  nf_register_hook(&nfho1);

  nfho2.hook     = hook_func2;
  nfho2.hooknum  = NF_IP_PRE_ROUTING;
  nfho2.pf       = PF_INET;
  nfho2.priority = NF_IP_PRI_FIRST;
  nf_register_hook(&nfho2);
  return 0;
}

static void __exit fini(void)
{
  nf_unregister_hook(&nfho1);
  nf_unregister_hook(&nfho2);
}
module_init(init);
module_exit(fini);
MODULE_LICENSE("GPL");

*************************************************************



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