netfilter notifiers. (hooks inside code called by hooks *g*)

The idea is to have a generic framework where kernel modules can register
all the events they can possibly generate, and all users can register their
event handlers for those events.

Requirements:

- efficient
- more than one event handler per event
- easy to use


#define NF_NOTIFIER_MAXPROV	4
#define NF_NOTIFIER_MAXEVT	8


struct nf_notifier_event {
	struct list_head list;
		
};

struct list_head nf_notifiers[NF_NOTIFIER_MAX_PROV][NF_NOTIFIER_MAX_EVT];

/* register a callback function with one of the events */
int nf_notifier_register(unsigned int prov_id, unsigned int evt_id,
			 struct nf_notifier_event *evt)
{
	if (prov_id > NF_NOTIFIER_MAXPROV ||
	    evt_id > NF_NOTIFIER_MAXEVT) 
		return -1;

	/* grab write lock */
	list_add(&nf_notifiers[prov_id][evt_id].list, &evt->list);
	/* unlock */

	return 0;
}

int nf_notifier_unregister(struct nf_notifier_event *evt)
{
	if (prov_id > NF_NOTIFIER_MAXPROV ||
	    evt_id > NF_NOTIFIER_MAXEVT)
		return -1;

	/* grab write lock */
	list_del(&evt->list);
	/* unlock */
}

int nf_notifier_call_slow(unsigned int prov_id, unsigned int evt_id,
			  int (*callback)(void *))
{
	struct list_head *elem, *i;
	struct ip_notifier_event *evt;

	/* don't check prov_id and evt_id ranges unless for debugging */

	/* grab read lock */
	elem = &nf_notifiers[prov_id][evt_id];
	for (i = elem; i != elem; i = i->next) {
		evt = (struct nf_hook_
	}
}

void __init nf_notifier_init(void)
{
	int i, h;

	for (i = 0; i < NPROTO; i++) {
		for (h = 0; h < NF_NOTIFIER_MAX_PROVIDERS; h++)
			INIT_LIST_HEAD(&nf_notifiers[i][h]);
	}
}