Index: sys/dev/netmap/if_tun_netmap.h
===================================================================
--- sys/dev/netmap/if_tun_netmap.h
+++ sys/dev/netmap/if_tun_netmap.h
@@ -0,0 +1,122 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 2020 Giuseppe Lettieri. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * $FreeBSD$
+ *
+ * netmap support for: tun
+ *
+ * The actual support comes from the netmap generic driver. The purpose of these
+ * functions is to make the tun device similar to an ethernet device, just enough
+ * for the generic driver to work with it.
+ *
+ * Two adjustments are needed:
+ *
+ * - In tunwrite(), when in netmap mode, we prepend a fake ethernet header that contains the family
+ * (AF_INET or AF_INET6) and then call the (overriden) if_input method;
+ *
+ * - We also provide the if_input method called by netmap when trying to inject packets
+ *   into the host stack
+ */
+
+
+#include <net/netmap.h>
+#include <sys/selinfo.h>
+#include <vm/vm.h>
+#include <vm/pmap.h> 
+#include <machine/bus.h>
+#include <machine/resource.h>
+#include <sys/bus.h>
+#include <sys/rman.h>
+#include <net/ethernet.h>
+#include <dev/netmap/netmap_kern.h>
+
+static void
+netmap_tuninput(struct ifnet *ifp, struct mbuf *m)
+{
+	struct epoch_tracker et;
+	struct ether_header *eh;
+	u_short etype;
+	int isr;
+
+	if (m->m_len < ETHER_HDR_LEN) {
+		nm_prlim(5, "discarding malformed mbuf (m->m_len == %d)", m->m_len);
+		goto error;
+	}
+	eh = mtod(m, struct ether_header *);
+	etype = ntohs(eh->ether_type);
+	switch (etype) {
+	case ETHERTYPE_IP:
+		isr = NETISR_IP;
+		break;
+	case ETHERTYPE_IPV6:
+		isr = NETISR_IPV6;
+		break;
+	default:
+		nm_prlim(5, "discarding packet with ethertype %02x", etype);
+		goto error;
+	}
+	m_adj(m, ETHER_HDR_LEN);
+	if_inc_counter(ifp, IFCOUNTER_IBYTES, m->m_pkthdr.len);
+	if_inc_counter(ifp, IFCOUNTER_IPACKETS, 1);
+	m->m_pkthdr.rcvif = ifp;
+	CURVNET_SET(ifp->if_vnet);
+	M_SETFIB(m, ifp->if_fib);
+	NET_EPOCH_ENTER(et);
+	netisr_dispatch(isr, m);
+	NET_EPOCH_EXIT(et);
+	CURVNET_RESTORE();
+
+	return;
+
+error:
+	if_inc_counter(ifp, IFCOUNTER_IERRORS, 1);
+	m_free(m);
+	return;
+}
+
+static int
+netmap_tuncapture(struct ifnet *ifp, int isr, struct mbuf *m)
+{
+	struct netmap_adapter *na = NA(ifp);
+	struct ether_header *eh;
+
+	if (!nm_netmap_on(na))
+		return 0;
+
+	M_PREPEND(m, ETHER_HDR_LEN, M_NOWAIT);
+	if (m == NULL) {
+		nm_prlim(5, "failed to prepend fake ethernet header, skipping");
+		return 0;
+	}
+	eh = mtod(m, struct ether_header *);
+	eh->ether_type = htons(isr == AF_INET6 ? ETHERTYPE_IPV6 : ETHERTYPE_IP);
+	(*ifp->if_input)(ifp, m);
+	return 1; /* stolen */
+}
+
+/* end of file */
Index: sys/net/if_tuntap.c
===================================================================
--- sys/net/if_tuntap.c
+++ sys/net/if_tuntap.c
@@ -110,6 +110,11 @@
 
 struct tuntap_driver;
 
+#ifdef DEV_NETMAP
+#include <dev/netmap/if_tun_netmap.h>
+MODULE_DEPEND(if_tun, netmap, 1, 1, 1);
+#endif /* DEV_NETMAP */
+
 /*
  * tun_list is protected by global tunmtx.  Other mutable fields are
  * protected by tun->tun_mtx, or by their owning subsystem.  tun_dev is
@@ -963,6 +968,9 @@
 	IFQ_SET_MAXLEN(&ifp->if_snd, ifqmaxlen);
 	ifp->if_capabilities |= IFCAP_LINKSTATE;
 	ifp->if_capenable |= IFCAP_LINKSTATE;
+#ifdef DEV_NETMAP
+	ifp->if_input = netmap_tuninput;
+#endif /* DEV_NETMAP */
 
 	if ((tp->tun_flags & TUN_L2) != 0) {
 		ifp->if_init = tunifinit;
@@ -1862,7 +1870,10 @@
 	CURVNET_SET(ifp->if_vnet);
 	M_SETFIB(m, ifp->if_fib);
 	NET_EPOCH_ENTER(et);
-	netisr_dispatch(isr, m);
+#ifdef DEV_NETMAP
+	if (!netmap_tuncapture(ifp, isr, m))
+#endif /* DEV_NETMAP */
+		netisr_dispatch(isr, m);
 	NET_EPOCH_EXIT(et);
 	CURVNET_RESTORE();
 	return (0);