다음의 에러를 해결하려면 어떻게 해야 하나요?

kldp bbs 게시판 내용 중에서 본 Roll Your Own Firewall with Netfilter 문서를 보고 그대로 따라했는데 컴파일을 하니 다음과 같은 에러가 생깁니다.
관련에러로 구글에 검색을 해보고 나온대로 해봐도 같은 에러가 나옵니다.
어떻게 해결할 수 있을까요?
고수님들의 답변을 부탁드립니다.
참 사용하는 리눅스는 데비안 2.4.18입니다.

=================== 소스 ======================
#define __KERNEL__
#define MODULE

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include </usr/src/linux/include/linux/netfilter.h>
static struct nf_hook_ops netfilter_ops_in; /* NF_IP_PRE_ROUTING */
static struct nf_hook_ops netfilter_ops_out; /* NF_IP_POST_ROUTING */

/* Function prototype in <linux/netfilter> */
unsigned int main_hook(unsigned int hooknum,
struct sk_buff **skb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff*))
{
return NF_DROP; /* Drop ALL Packets */
}

int init_module()
{

netfilter_ops_in.hook = main_hook;
netfilter_ops_in.pf = PF_INET;
netfilter_ops_in.hooknum = NF_IP_PRE_ROUTING;
netfilter_ops_in.priority = NF_IP_PRI_FIRST;

netfilter_ops_out.hook = main_hook;
netfilter_ops_out.pf = PF_INET;
netfilter_ops_out.hooknum = NF_IP_POST_ROUTING;
netfilter_ops_out.priority = NF_IP_PRI_FIRST;

nf_register_hook(&netfilter_ops_in); /* register NF_IP_PRE_ROUTING hook */
nf_register_hook(&netfilter_ops_out); /* register NF_IP_POST_ROUTING hook */

return 0;
}

void cleanup()
{
nf_unregister_hook(&netfilter_ops_in); /*unregister NF_IP_PRE_ROUTING hook*/
nf_unregister_hook(&netfilter_ops_out); /*unregister NF_IP_POST_ROUTING hook*/
}
==============================================

에러내용

# gcc -c drop.c
drop.c: In function `init_module':
drop.c:26: invalid use of undefined type `struct nf_hook_ops'
drop.c:27: invalid use of undefined type `struct nf_hook_ops'
drop.c:28: invalid use of undefined type `struct nf_hook_ops'
drop.c:29: invalid use of undefined type `struct nf_hook_ops'
drop.c:31: invalid use of undefined type `struct nf_hook_ops'
drop.c:32: invalid use of undefined type `struct nf_hook_ops'
drop.c:33: invalid use of undefined type `struct nf_hook_ops'
drop.c:34: invalid use of undefined type `struct nf_hook_ops'
drop.c: At top level:
drop.c:9: storage size of `netfilter_ops_in' isn't known
drop.c:10: storage size of `netfilter_ops_out' isn't known
#

원문링크
http://www.linuxjournal.com/article.php?sid=7184