NetFilter

1. typedef unsigned int nf_hookfn(unsigned int hooknum,

2. struct sk_buff *skb,

3. const struct net_device *in,

4. const struct net_device *out,

5. int (*okfn) (struct sk_buff *));

6. /* 处理函数返回值 */

7. #define NF_DROP 0 /* drop the packet, don't continue traversal */

8. #define NF_ACCEPT 1 /* continue traversal as normal */

9. #define NF_STOLEN 2 /* I've taken over the packet, don't continue traversal */

10. #define NF_QUEUE 3 /* queue the packet (usually for userspace handling) */

11. #define NF_REPEAT 4 /* call this hook again */

12. #define NF_STOP 5

13. #define NF_MAX_VERDICT NF_STOP

在使用Netfilter时，需要定义一个nf_hook_ops实例。

1. struct nf_hook_ops {

2. struct list_head list;

3. /* User fills in from here down. */

4. nf_hookfn *hook; /* 要注册的钩子函数 */

5. struct module *owner;

6. u_int8_t pf; /* 协议类型 */

7. unsigned int hooknum; /* 哪个钓鱼台 */

8. /* Hooks are ordered in asending priority. */

9. int priority; /* 数值越小，优先级越高 */

10. };

11. typedef __u8 u_int8_t;