diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -313,6 +313,10 @@
 static void	unp_addsockcred(struct thread *, struct mchain *, int);
 static void	unp_process_defers(void * __unused, int);
 
+static void	uipc_wrknl_lock(void *);
+static void	uipc_wrknl_unlock(void *);
+static void	uipc_wrknl_assert_lock(void *, int);
+
 static void
 unp_pcb_hold(struct unpcb *unp)
 {
@@ -505,6 +509,8 @@
 		sendspace = unpsp_sendspace;
 		recvspace = unpsp_recvspace;
 common:
+		knlist_init(&so->so_wrsel.si_note, so, uipc_wrknl_lock,
+		    uipc_wrknl_unlock, uipc_wrknl_assert_lock);
 		STAILQ_INIT(&so->so_rcv.uxst_mbq);
 		break;
 	default:
@@ -1576,6 +1582,172 @@
 	return (revents);
 }
 
+static void
+uipc_wrknl_lock(void *arg)
+{
+	struct socket *so = arg;
+	struct unpcb *unp = sotounpcb(so), *unp2;
+
+retry:
+	if (SOLISTENING(so)) {
+		SOLISTEN_LOCK(so);
+	} else {
+		UNP_PCB_LOCK(unp);
+		if (__predict_false(SOLISTENING(so))) {
+			UNP_PCB_UNLOCK(unp);
+			goto retry;
+		}
+		if ((unp2 = unp_pcb_lock_peer(unp)) != NULL) {
+			MPASS(unp != unp2);
+			SOCK_RECVBUF_LOCK(unp2->unp_socket);
+		}
+	}
+}
+
+static void
+uipc_wrknl_unlock(void *arg)
+{
+	struct socket *so = arg;
+	struct unpcb *unp = sotounpcb(so), *unp2 = unp->unp_conn;
+
+	if (SOLISTENING(so))
+		SOLISTEN_UNLOCK(so);
+	else {
+		if (unp2 != NULL) {
+			SOCK_RECVBUF_UNLOCK(unp2->unp_socket);
+			UNP_PCB_UNLOCK(unp2);
+		}
+		UNP_PCB_UNLOCK(unp);
+	}
+}
+
+static void
+uipc_wrknl_assert_lock(void *arg, int what)
+{
+	struct socket *so = arg;
+	struct unpcb *unp = sotounpcb(so), *unp2 = unp->unp_conn;
+
+	if (SOLISTENING(so)) {
+		if (what == LA_LOCKED)
+			SOLISTEN_LOCK_ASSERT(so);
+		else
+			SOLISTEN_UNLOCK_ASSERT(so);
+	} else {
+		if (what == LA_LOCKED) {
+			UNP_PCB_LOCK_ASSERT(unp);
+			if (unp2 != NULL) {
+				UNP_PCB_LOCK_ASSERT(unp2);
+				SOCK_RECVBUF_LOCK_ASSERT(unp2->unp_socket);
+			}
+		} else
+			UNP_PCB_UNLOCK_ASSERT(unp);
+	}
+}
+
+static void
+uipc_filt_sowdetach(struct knote *kn)
+{
+	struct socket *so = kn->kn_fp->f_data;
+	struct unpcb *unp = sotounpcb(so), *unp2;
+
+	uipc_wrknl_lock(so);
+	knlist_remove(&so->so_wrsel.si_note, kn, 1);
+	if (!SOLISTENING(so) && knlist_empty(&so->so_wrsel.si_note) &&
+	    (unp2 = unp->unp_conn) != NULL)
+		unp2->unp_socket->so_rcv.sb_flags &= ~SB_KNOTE;
+	uipc_wrknl_unlock(so);
+}
+
+static int
+uipc_filt_sowrite(struct knote *kn, long hint)
+{
+	struct socket *so = kn->kn_fp->f_data, *so2;
+	struct unpcb *unp = sotounpcb(so), *unp2 = unp->unp_conn;
+
+	if (SOLISTENING(so) || unp2 == NULL)
+		return (0);
+
+	so2 = unp2->unp_socket;
+	SOCK_RECVBUF_LOCK_ASSERT(so2);
+	kn->kn_data = uipc_stream_sbspace(&so2->so_rcv);
+
+	if (so2->so_rcv.sb_state & SBS_CANTRCVMORE) {
+		kn->kn_flags |= EV_EOF;
+		kn->kn_fflags = so->so_error;
+		return (1);
+	} else if (kn->kn_sfflags & NOTE_LOWAT)
+		return (kn->kn_data >= kn->kn_sdata);
+	else
+		return (kn->kn_data >= so2->so_snd.sb_lowat);
+}
+
+static int
+uipc_filt_soempty(struct knote *kn, long hint)
+{
+	struct socket *so = kn->kn_fp->f_data, *so2;
+	struct unpcb *unp = sotounpcb(so), *unp2 = unp->unp_conn;
+
+	if (SOLISTENING(so) || unp2 == NULL)
+		return (1);
+
+	so2 = unp2->unp_socket;
+	SOCK_RECVBUF_LOCK_ASSERT(so2);
+	kn->kn_data = uipc_stream_sbspace(&so2->so_rcv);
+
+	return (kn->kn_data == 0 ? 1 : 0);
+}
+
+static const struct filterops uipc_write_filtops = {
+	.f_isfd = 1,
+	.f_detach = uipc_filt_sowdetach,
+	.f_event = uipc_filt_sowrite,
+};
+static const struct filterops uipc_empty_filtops = {
+	.f_isfd = 1,
+	.f_detach = uipc_filt_sowdetach,
+	.f_event = uipc_filt_soempty,
+};
+
+static int
+uipc_kqfilter_stream_or_seqpacket(struct socket *so, struct knote *kn)
+{
+	struct unpcb *unp = sotounpcb(so), *unp2;
+	struct knlist *knl;
+
+	switch (kn->kn_filter) {
+	case EVFILT_READ:
+		return (sokqfilter_generic(so, kn));
+	case EVFILT_WRITE:
+		kn->kn_fop = &uipc_write_filtops;
+		break;
+	case EVFILT_EMPTY:
+		kn->kn_fop = &uipc_empty_filtops;
+		break;
+	default:
+		return (EINVAL);
+	}
+
+	knl = &so->so_wrsel.si_note;
+	UNP_PCB_LOCK(unp);
+	if (SOLISTENING(so)) {
+		knlist_add(knl, kn, 1);
+	} else {
+		if ((unp2 = unp_pcb_lock_peer(unp)) != NULL) {
+			MPASS(unp != unp2);
+			SOCK_RECVBUF_LOCK(unp2->unp_socket);
+			knlist_add(knl, kn, 1);
+			unp2->unp_socket->so_rcv.sb_flags |= SB_KNOTE;
+			SOCK_RECVBUF_UNLOCK(unp2->unp_socket);
+			UNP_PCB_UNLOCK(unp2);
+		} else {
+			UNP_PCB_UNLOCK(unp);
+			return (ENOTCONN);
+		}
+	}
+	UNP_PCB_UNLOCK(unp);
+	return (0);
+}
+
 /* PF_UNIX/SOCK_DGRAM version of sbspace() */
 static inline bool
 uipc_dgram_sbspace(struct sockbuf *sb, u_int cc, u_int mbcnt)
@@ -3948,6 +4120,7 @@
 	.pr_sosend = 		uipc_sosend_stream_or_seqpacket,
 	.pr_soreceive =		uipc_soreceive_stream_or_seqpacket,
 	.pr_sopoll =		uipc_sopoll_stream_or_seqpacket,
+	.pr_kqfilter =		uipc_kqfilter_stream_or_seqpacket,
 	.pr_close =		uipc_close,
 	.pr_chmod =		uipc_chmod,
 };
@@ -3998,6 +4171,7 @@
 	.pr_sosend = 		uipc_sosend_stream_or_seqpacket,
 	.pr_soreceive =		uipc_soreceive_stream_or_seqpacket,
 	.pr_sopoll =		uipc_sopoll_stream_or_seqpacket,
+	.pr_kqfilter =		uipc_kqfilter_stream_or_seqpacket,
 	.pr_close =		uipc_close,
 	.pr_chmod =		uipc_chmod,
 };