include/linux/netfilter.h

#ifndef __LINUX_NETFILTER_H
#define __LINUX_NETFILTER_H

#ifdef __KERNEL__
#include <linux/init.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/net.h>
#include <linux/if.h>
#include <linux/wait.h>
#include <linux/list.h>
#endif
#include <linux/compiler.h>

/* Responses from hook functions. */
#define NF_DROP 0
#define NF_ACCEPT 1
#define NF_STOLEN 2
#define NF_QUEUE 3
#define NF_REPEAT 4
#define NF_STOP 5
#define NF_MAX_VERDICT NF_STOP

/* we overload the higher bits for encoding auxiliary data such as the queue
 * number. Not nice, but better than additional function arguments. */
#define NF_VERDICT_MASK 0x0000ffff
#define NF_VERDICT_BITS 16

#define NF_VERDICT_QMASK 0xffff0000
#define NF_VERDICT_QBITS 16

#define NF_QUEUE_NR(x) ((x << NF_VERDICT_QBITS) & NF_VERDICT_QMASK || NF_QUEUE)

/* only for userspace compatibility */
#ifndef __KERNEL__
/* Generic cache responses from hook functions.
   <= 0x2000 is used for protocol-flags. */
#define NFC_UNKNOWN 0x4000
#define NFC_ALTERED 0x8000
#endif

#ifdef __KERNEL__
#include <linux/config.h>
#ifdef CONFIG_NETFILTER

extern void netfilter_init(void);

/* Largest hook number + 1 */
#define NF_MAX_HOOKS 8

struct sk_buff;
struct net_device;

typedef unsigned int nf_hookfn(unsigned int hooknum,
			       struct sk_buff **skb,
			       const struct net_device *in,
			       const struct net_device *out,
			       int (*okfn)(struct sk_buff *));

struct nf_hook_ops
{
	struct list_head list;

	/* User fills in from here down. */
	nf_hookfn *hook;
	struct module *owner;
	int pf;
	int hooknum;
	/* Hooks are ordered in ascending priority. */
	int priority;
};

struct nf_sockopt_ops
{
	struct list_head list;

	int pf;

	/* Non-inclusive ranges: use 0/0/NULL to never get called. */
	int set_optmin;
	int set_optmax;
	int (*set)(struct sock *sk, int optval, void __user *user, unsigned int len);

	int get_optmin;
	int get_optmax;
	int (*get)(struct sock *sk, int optval, void __user *user, int *len);

	/* Number of users inside set() or get(). */
	unsigned int use;
	struct task_struct *cleanup_task;
};

/* Each queued (to userspace) skbuff has one of these. */
struct nf_info
{
	/* The ops struct which sent us to userspace. */
	struct nf_hook_ops *elem;
	
	/* If we're sent to userspace, this keeps housekeeping info */
	int pf;
	unsigned int hook;
	struct net_device *indev, *outdev;
	int (*okfn)(struct sk_buff *);
};
                                                                                
/* Function to register/unregister hook points. */
int nf_register_hook(struct nf_hook_ops *reg);
void nf_unregister_hook(struct nf_hook_ops *reg);

/* Functions to register get/setsockopt ranges (non-inclusive).  You
   need to check permissions yourself! */
int nf_register_sockopt(struct nf_sockopt_ops *reg);
void nf_unregister_sockopt(struct nf_sockopt_ops *reg);

extern struct list_head nf_hooks[NPROTO][NF_MAX_HOOKS];

typedef void nf_logfn(unsigned int hooknum,
		      const struct sk_buff *skb,
		      const struct net_device *in,
		      const struct net_device *out,
		      const char *prefix);

/* Function to register/unregister log function. */
int nf_log_register(int pf, nf_logfn *logfn);
void nf_log_unregister(int pf, nf_logfn *logfn);

/* Calls the registered backend logging function */
void nf_log_packet(int pf,
		   unsigned int hooknum,
		   const struct sk_buff *skb,
		   const struct net_device *in,
		   const struct net_device *out,
		   const char *fmt, ...);
                   
/* Activate hook; either okfn or kfree_skb called, unless a hook
   returns NF_STOLEN (in which case, it's up to the hook to deal with
   the consequences).

   Returns -ERRNO if packet dropped.  Zero means queued, stolen or
   accepted.
*/

/* RR:
   > I don't want nf_hook to return anything because people might forget
   > about async and trust the return value to mean "packet was ok".

   AK:
   Just document it clearly, then you can expect some sense from kernel
   coders :)
*/

/* This is gross, but inline doesn't cut it for avoiding the function
   call in fast path: gcc doesn't inline (needs value tracking?). --RR */
#ifdef CONFIG_NETFILTER_DEBUG
#define NF_HOOK(pf, hook, skb, indev, outdev, okfn)			       \
({int __ret;								       \
if ((__ret=nf_hook_slow(pf, hook, &(skb), indev, outdev, okfn, INT_MIN)) == 1) \
	__ret = (okfn)(skb);						       \
__ret;})
#define NF_HOOK_THRESH(pf, hook, skb, indev, outdev, okfn, thresh)	       \
({int __ret;								       \
if ((__ret=nf_hook_slow(pf, hook, &(skb), indev, outdev, okfn, thresh)) == 1)  \
	__ret = (okfn)(skb);						       \
__ret;})
#else
#define NF_HOOK(pf, hook, skb, indev, outdev, okfn)			       \
({int __ret;								       \
if (list_empty(&nf_hooks[pf][hook]) ||					       \
    (__ret=nf_hook_slow(pf, hook, &(skb), indev, outdev, okfn, INT_MIN)) == 1) \
	__ret = (okfn)(skb);						       \
__ret;})
#define NF_HOOK_THRESH(pf, hook, skb, indev, outdev, okfn, thresh)	       \
({int __ret;								       \
if (list_empty(&nf_hooks[pf][hook]) ||					       \
    (__ret=nf_hook_slow(pf, hook, &(skb), indev, outdev, okfn, thresh)) == 1)  \
	__ret = (okfn)(skb);						       \
__ret;})
#endif

int nf_hook_slow(int pf, unsigned int hook, struct sk_buff **pskb,
		 struct net_device *indev, struct net_device *outdev,
		 int (*okfn)(struct sk_buff *), int thresh);

/* Call setsockopt() */
int nf_setsockopt(struct sock *sk, int pf, int optval, char __user *opt, 
		  int len);
int nf_getsockopt(struct sock *sk, int pf, int optval, char __user *opt,
		  int *len);

/* Packet queuing */
typedef int (*nf_queue_outfn_t)(struct sk_buff *skb, 
                                struct nf_info *info,
				unsigned int queuenum, void *data);
extern int nf_register_queue_handler(int pf, 
                                     nf_queue_outfn_t outfn, void *data);
extern int nf_unregister_queue_handler(int pf);
extern void nf_unregister_queue_handlers(nf_queue_outfn_t outfn);
extern void nf_reinject(struct sk_buff *skb,
			struct nf_info *info,
			unsigned int verdict);

extern void (*ip_ct_attach)(struct sk_buff *, struct sk_buff *);
extern void nf_ct_attach(struct sk_buff *, struct sk_buff *);

/* FIXME: Before cache is ever used, this must be implemented for real. */
extern void nf_invalidate_cache(int pf);

/* Call this before modifying an existing packet: ensures it is
   modifiable and linear to the point you care about (writable_len).
   Returns true or false. */
extern int skb_make_writable(struct sk_buff **pskb, unsigned int writable_len);

struct nf_queue_rerouter {
	void (*save)(const struct sk_buff *skb, struct nf_info *info);
	int (*reroute)(struct sk_buff **skb, const struct nf_info *info);
	int rer_size;
};

#define nf_info_reroute(x) ((void *)x + sizeof(struct nf_info))

extern int nf_register_queue_rerouter(int pf, struct nf_queue_rerouter *rer);
extern int nf_unregister_queue_rerouter(int pf);

#else /* !CONFIG_NETFILTER */
#define NF_HOOK(pf, hook, skb, indev, outdev, okfn) (okfn)(skb)
static inline void nf_ct_attach(struct sk_buff *new, struct sk_buff *skb) {}
#endif /*CONFIG_NETFILTER*/

#endif /*__KERNEL__*/
#endif /*__LINUX_NETFILTER_H*/