#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
 
static unsigned int my_nf_hookfn(unsigned int hooknum,
				 struct sk_buff *skb,
			 	 const struct net_device *in,
				 const struct net_device *out,
				 int (*okfn)(struct sk_buff *))
{
	/* process packet */
	//...
 
	return NF_ACCEPT;
}
 
static struct nf_hook_ops my_nfho = {
	.owner       = THIS_MODULE,
	.hook        = my_nf_hookfn,
	.hooknum     = NF_IP_LOCAL_IN,
	.pf          = PF_INET,
	.priority    = NF_IP_PRI_FIRST
};
 
int __init my_hook_init(void)
{
	return nf_register_hook(&my_nfho);
}
 
void __exit my_hook_exit(void)
{
	nf_unregister_hook(&my_nfho);
}
 
module_init(my_hook_init);
module_exit(my_hook_exit);