diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -1398,10 +1398,11 @@
 }
 
 int
-kqueue_add_filteropts(int filt, const struct filterops *filtops)
+kqueue_assign_filteropts(int *filtp, struct filterops *filtops)
 {
-	int error;
+	int error, filt, i;
 
+	filt = *filtp;
 	error = 0;
 	if (filt > 0 || filt + EVFILT_SYSCOUNT < 0) {
 		printf(
@@ -1410,10 +1411,19 @@
 		return EINVAL;
 	}
 	mtx_lock(&filterops_lock);
-	if (sysfilt_ops[~filt].for_fop != &null_filtops &&
+	if (filt == NO_EVFILT) {
+		for (i = EVFILT_USER_START; ~i < EVFILT_SYSCOUNT; i--)
+			if (sysfilt_ops[~i].for_fop == &null_filtops ||
+			    sysfilt_ops[~i].for_fop == NULL)
+				break;
+		if (~i == EVFILT_SYSCOUNT)
+			error = ENFILE;
+		else
+			filt = i;	/* record the index */
+	} else if (sysfilt_ops[~filt].for_fop != &null_filtops &&
 	    sysfilt_ops[~filt].for_fop != NULL)
 		error = EEXIST;
-	else {
+	if (error == 0) {
 		sysfilt_ops[~filt].for_fop = filtops;
 		sysfilt_ops[~filt].for_refcnt = 0;
 	}
@@ -1422,6 +1432,15 @@
 	return (error);
 }
 
+int
+kqueue_add_filteropts(int filt, struct filterops *filtops)
+{
+	if (filt == NO_EVFILT)
+		return (EINVAL);
+
+	return kqueue_assign_filteropts(&filt, filtops);
+}
+
 int
 kqueue_del_filteropts(int filt)
 {
@@ -2829,3 +2848,41 @@
 	fdrop(fp, td);
 	return (error);
 }
+
+int
+kevent_module_handler(struct module *mod, int what, void *arg)
+{
+	struct kevent_module_data *data = arg;
+	modspecific_t ms;
+	int error;
+
+	switch (what) {
+	case MOD_LOAD:
+		if (data->offset != NO_EVFILT &&
+		    data->offset > EVFILT_USER_START) {
+			if (bootverbose)
+				printf("%s: Invalid slot %d\n", __func__,
+				    data->offset);
+			return (EINVAL);
+		}
+		error = kqueue_assign_filteropts(&data->offset, data->filt_ops);
+		if (error) {
+			data->offset = NO_EVFILT;
+			return (error);
+		}
+		ms.intval = data->offset;
+		MOD_XLOCK;
+		module_setspecific(mod, &ms);
+		MOD_XUNLOCK;
+		return (error);
+	case MOD_UNLOAD:
+		if (data->offset == NO_EVFILT)
+			return (0);
+		error = kqueue_del_filteropts(data->offset);
+		return (error);
+	default:
+		break;
+	}
+
+	return (EOPNOTSUPP);
+}
diff --git a/sys/sys/event.h b/sys/sys/event.h
--- a/sys/sys/event.h
+++ b/sys/sys/event.h
@@ -45,7 +45,9 @@
 #define EVFILT_USER		(-11)	/* User events */
 #define EVFILT_SENDFILE		(-12)	/* attached to sendfile requests */
 #define EVFILT_EMPTY		(-13)	/* empty send socket buf */
-#define EVFILT_SYSCOUNT		13
+#define EVFILT_SYSCOUNT		32
+#define NO_EVFILT		(0)	/* request for dynamic registration */
+#define EVFILT_USER_START	(-17)	/* User defined slots start */
 
 #if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
 #define	EV_SET(kevp_, a, b, c, d, e, f) do {	\
@@ -322,12 +324,31 @@
 	size_t	kevent_size;
 };
 
+struct kevent_module_data {
+	const char	*name;		/* name of kernel event */
+	int		offset;		/* offset */
+	struct filterops *filt_ops;	/* defined filtops */
+};
+
 struct thread;
 struct proc;
 struct knlist;
+struct module;
 struct mtx;
 struct rwlock;
 
+#define KEVENT_MODULE(name, offset, new_filtops)		\
+	static struct kevent_module_data name##_kevent_mod = {	\
+		"kevent/" #name, offset, new_filtops		\
+	};                                                      \
+	static moduledata_t name##_mod = {                      \
+		"kevent/" #name,                                \
+		kevent_module_handler,                          \
+		&name##_kevent_mod                              \
+	};                                                      \
+	DECLARE_MODULE(name, name##_mod, SI_SUB_SYSCALLS, SI_ORDER_MIDDLE)
+
+int	kevent_module_handler(struct module *mod, int what, void *arg);
 void	knote(struct knlist *list, long hint, int lockflags);
 void	knote_fork(struct knlist *list, int pid);
 struct knlist *knlist_alloc(struct mtx *lock);
@@ -349,6 +370,7 @@
 int 	kqfd_register(int fd, struct kevent *kev, struct thread *p,
 	    int mflag);
 int	kqueue_add_filteropts(int filt, const struct filterops *filtops);
+int	kqueue_assign_filteropts(int *filtp, struct filterops *filtops);
 int	kqueue_del_filteropts(int filt);
 void	kqueue_drain_schedtask(void);