Function hhook_add_hook

freebsd/kern/kern_hhook.c:132–172

* Register a new helper hook function with a helper hook point. */

 * Register a new helper hook function with a helper hook point.
 */
int
hhook_add_hook(struct hhook_head *hhh, struct hookinfo *hki, uint32_t flags)
{
	struct hhook *hhk, *tmp;
	int error;

	error = 0;

	if (hhh == NULL)
		return (ENOENT);

	hhk = malloc(sizeof(struct hhook), M_HHOOK,
	    M_ZERO | ((flags & HHOOK_WAITOK) ? M_WAITOK : M_NOWAIT));

	if (hhk == NULL)
		return (ENOMEM);

	hhk->hhk_helper = hki->hook_helper;
	hhk->hhk_func = hki->hook_func;
	hhk->hhk_udata = hki->hook_udata;

	HHH_WLOCK(hhh);
	STAILQ_FOREACH(tmp, &hhh->hhh_hooks, hhk_next) {
		if (tmp->hhk_func == hki->hook_func &&
		    tmp->hhk_udata == hki->hook_udata) {
			/* The helper hook function is already registered. */
			error = EEXIST;
			break;
		}
	}

	if (!error) {
		STAILQ_INSERT_TAIL(&hhh->hhh_hooks, hhk, hhk_next);
		hhh->hhh_nhooks++;
	} else
		free(hhk, M_HHOOK);

	HHH_WUNLOCK(hhh);

	return (error);
}

/*
 * Register a helper hook function with a helper hook point (including all