Merge from p4: CH154790,154793,154874

  Import if_epair(4), a virtual cross-over Ethernet-like interface pair.

Note these files are 1:1 from p4 and not yet connected to the build
not knowing about the new netisr interface.

Sponsored by:	The FreeBSD Foundation

2 files changed, 848 insertions, 0 deletions

diff --git a/share/man/man4/epair.4 b/share/man/man4/epair.4
new file mode 100644
index 0000000..b93d36e
--- /dev/null
+++ b/share/man/man4/epair.4
@@ -0,0 +1,120 @@
+.\"-
+.\" Copyright (c) 2008 The FreeBSD Foundation
+.\" All rights reserved.
+.\"
+.\" This software was developed by CK Software GmbH under sponsorship
+.\" from the FreeBSD Foundation.
+.\"
+.\" 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.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd December 15, 2008
+.Dt EPAIR 4
+.Os
+.Sh NAME
+.Nm epair
+.Nd Virtual cross-over Ethernet-like interface pair.
+.Sh SYNOPSIS
+To compile this driver into the kernel,
+place the following line in your
+kernel configuration file:
+.Bd -ragged -offset indent
+.Cd "device epair"
+.Ed
+.Pp
+Alternatively, to load the driver as a
+module at boot time, place the following line in
+.Xr loader.conf 5 :
+.Bd -literal -offset indent
+if_epair_load="YES"
+.Ed
+.Sh DESCRIPTION
+The
+.Nm
+is a pair of Ethernet-like software interfaces,
+which are directly connected by a virtual cross-over cable.
+.Pp
+Each
+.Nm
+interface pair is created at runtime using interface cloning.
+This is most easily done with the
+.Xr ifconfig 8
+.Cm create
+command or using the
+.Va cloned_interfaces
+variable in
+.Xr rc.conf 5 .
+While for cloning you only give either
+.Pa epair
+or
+.Pa epair<n>
+the
+.Nm
+pair will be named like
+.Pa epair<n>[ab] .
+This means the names of the first
+.Nm
+interfaces will be
+.Pa epair0a
+and
+.Pa epair0b .
+.Pp
+Like any other Ethernet interface, an
+.Nm
+needs to have a network address.
+Each
+.Nm
+will be assigned a locally administered address by default,
+that is only guaranteed to be unique within one network stack.
+To change the default addresses one may use the SIOCSIFADDR ioctl(2) or
+ifconfig(8) utility.
+.Pp
+The basic intend is to provide connectivity between two virtual
+network stack instances.
+When connected to a
+.Xr if_bridge 4
+one end of the interface pair can also be part of another (virtual) LAN.
+As with any other Ethernet interface one can configure
+.Xr vlan 4
+support on top of it.
+.Pp
+.Sh SEE ALSO
+.Xr ioctl 2 ,
+.Xr altq 4 ,
+.Xr bpf 4 ,
+.Xr if_bridge 4 ,
+.Xr vlan 4 ,
+.Xr loader.conf 5, 
+.Xr rc.conf 5 ,
+.Xr ifconfig 8
+.Sh HISTORY
+The
+.Nm
+interface first appeared in
+.Fx 8.0 .
+.Sh AUTHORS
+The
+.Nm
+interface was written by
+.An Bjoern A. Zeeb, CK Software GmbH,
+under sponsorship from the FreeBSD Foundation.
diff --git a/sys/net/if_epair.c b/sys/net/if_epair.c
new file mode 100644
index 0000000..8a5c8a5
--- /dev/null
+++ b/sys/net/if_epair.c
@@ -0,0 +1,728 @@
+/*-
+ * Copyright (c) 2008 The FreeBSD Foundation
+ * All rights reserved.
+ *
+ * This software was developed by CK Software GmbH under sponsorship
+ * from the FreeBSD Foundation.
+ *
+ * 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.
+ */
+
+/*
+ * A pair of virtual ethernet interfaces directly connected with
+ * a virtual cross-over cable.
+ * This is mostly intended to be used to provide connectivity between
+ * different virtual network stack instances.
+ */
+/*
+ * Things to re-think once we have more experience:
+ * - ifp->if_reassign function once we can test with vimage.
+ * - Real random etheraddrs that are checked to be uniquish;
+ *   in case we bridge we may need this or let the user handle that case?
+ * - netisr and callback logic.
+ * - netisr queue lengths.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/mbuf.h>
+#include <sys/module.h>
+#include <sys/refcount.h>
+#include <sys/queue.h>
+#include <sys/socket.h>
+#include <sys/sockio.h>
+#include <sys/sysctl.h>
+#include <sys/types.h>
+#include <sys/vimage.h>
+
+#include <net/bpf.h>
+#include <net/ethernet.h>
+#include <net/if.h>
+#include <net/if_clone.h>
+#include <net/if_var.h>
+#include <net/if_types.h>
+#include <net/netisr.h>
+
+#define	EPAIRNAME	"epair"
+
+#ifdef DEBUG_EPAIR
+static int epair_debug = 0;
+SYSCTL_DECL(_net_link);
+SYSCTL_NODE(_net_link, OID_AUTO, epair, CTLFLAG_RW, 0, "epair sysctl");
+SYSCTL_XINT(_net_link_epair, OID_AUTO, epair_debug, CTLFLAG_RW,
+    &epair_debug, 0, "if_epair(4) debugging.");
+#define	DPRINTF(fmt, arg...)	if (epair_debug) \
+    printf("[%s:%d] " fmt, __func__, __LINE__, ##arg)
+#else
+#define	DPRINTF(fmt, arg...)
+#endif
+
+struct epair_softc {
+	struct ifnet	*ifp;
+	struct ifnet	*oifp;
+	u_int		refcount;
+	void		(*if_qflush)(struct ifnet *);
+};
+
+struct epair_ifp_drain {
+	STAILQ_ENTRY(epair_ifp_drain)	ifp_next;
+	struct ifnet			*ifp;
+};
+
+static STAILQ_HEAD(, epair_ifp_drain) epair_ifp_drain_list =
+    STAILQ_HEAD_INITIALIZER(epair_ifp_drain_list);
+
+#define ADD_IFQ_FOR_DRAINING(ifp)					\
+	do {								\
+		struct epair_ifp_drain *elm = NULL;			\
+									\
+		STAILQ_FOREACH(elm, &epair_ifp_drain_list, ifp_next) {	\
+			if (elm->ifp == (ifp))				\
+				break;					\
+		}							\
+		if (elm == NULL) {					\
+			elm = malloc(sizeof(struct epair_ifp_drain),	\
+			    M_EPAIR, M_ZERO);				\
+			if (elm != NULL) {				\
+				elm->ifp = (ifp);			\
+				STAILQ_INSERT_TAIL(			\
+				    &epair_ifp_drain_list,		\
+			    	    elm, ifp_next);			\
+			}						\
+		}							\
+	} while(0)
+
+/* Our "hw" tx queue. */
+static struct ifqueue epairinq;
+static int epair_drv_flags;
+
+static struct mtx if_epair_mtx;
+#define	EPAIR_LOCK_INIT()	mtx_init(&if_epair_mtx, "if_epair", \
+				    NULL, MTX_DEF)
+#define	EPAIR_LOCK_DESTROY()	mtx_destroy(&if_epair_mtx)
+#define	EPAIR_LOCK_ASSERT()	mtx_assert(&if_epair_mtx, MA_OWNED)
+#define	EPAIR_LOCK()		mtx_lock(&if_epair_mtx)
+#define	EPAIR_UNLOCK()		mtx_unlock(&if_epair_mtx)
+
+static MALLOC_DEFINE(M_EPAIR, EPAIRNAME,
+    "Pair of virtual cross-over connected Ethernet-like interfaces");
+
+static int epair_clone_match(struct if_clone *, const char *);
+static int epair_clone_create(struct if_clone *, char *, size_t, caddr_t);
+static int epair_clone_destroy(struct if_clone *, struct ifnet *);
+
+static void epair_start_locked(struct ifnet *);
+
+static struct if_clone epair_cloner = IFC_CLONE_INITIALIZER(
+    EPAIRNAME, NULL, IF_MAXUNIT,
+    NULL, epair_clone_match, epair_clone_create, epair_clone_destroy);
+
+
+/*
+ * Netisr handler functions.
+ */
+static void
+epair_sintr(struct mbuf *m)
+{
+	struct ifnet *ifp;
+	struct epair_softc *sc;
+
+	ifp = m->m_pkthdr.rcvif;
+	(*ifp->if_input)(ifp, m);
+	sc = ifp->if_softc;
+	refcount_release(&sc->refcount);
+	DPRINTF("ifp=%p refcount=%u\n", ifp, sc->refcount);
+}
+
+static void
+epair_sintr_drained(void)
+{
+	struct epair_ifp_drain *elm, *tvar;
+	struct ifnet *ifp;
+
+	EPAIR_LOCK();
+	/*
+	 * Assume our "hw" queue and possibly ifq will be emptied
+	 * again. In case we will overflow the "hw" queue while
+	 * draining, epair_start_locked will set IFF_DRV_OACTIVE
+	 * again and we will stop and return.
+	 */
+	STAILQ_FOREACH_SAFE(elm, &epair_ifp_drain_list, ifp_next, tvar) {
+		ifp = elm->ifp;
+		epair_drv_flags &= ~IFF_DRV_OACTIVE;
+		ifp->if_drv_flags &= ~IFF_DRV_OACTIVE;
+		epair_start_locked(ifp);
+
+		IFQ_LOCK(&ifp->if_snd);
+		if (IFQ_IS_EMPTY(&ifp->if_snd)) {
+			STAILQ_REMOVE(&epair_ifp_drain_list, elm,
+			    epair_ifp_drain, ifp_next);
+			free(elm, M_EPAIR);
+		}
+		IFQ_UNLOCK(&ifp->if_snd);
+
+		if ((ifp->if_drv_flags & IFF_DRV_OACTIVE) != 0) {
+			/* Our "hw"q overflew again. */
+			epair_drv_flags |= IFF_DRV_OACTIVE
+			DPRINTF("hw queue length overflow at %u\n",
+			    epairinq.ifq_maxlen);
+#if 0
+			/* ``Auto-tuning.'' */
+			epairinq.ifq_maxlen += ifqmaxlen;
+#endif
+			break;
+		}
+	}
+	EPAIR_UNLOCK();
+}
+
+/*
+ * Network interface (`if') related functions.
+ */
+static void
+epair_start_locked(struct ifnet *ifp)
+{
+	struct mbuf *m;
+	struct epair_softc *sc;
+	struct ifnet *oifp;
+	int error;
+
+	EPAIR_LOCK_ASSERT();
+	DPRINTF("ifp=%p\n", ifp);
+
+	if ((ifp->if_drv_flags & IFF_DRV_RUNNING) == 0)
+		return;
+	if ((ifp->if_flags & IFF_UP) == 0)
+		return;
+
+	/*
+	 * We get patckets here from ether_output via if_handoff()
+	 * and ned to put them into the input queue of the oifp
+	 * and call oifp->if_input() via netisr/epair_sintr().
+	 */
+	sc = ifp->if_softc;
+	oifp = sc->oifp;
+	sc = oifp->if_softc;
+	for (;;) {
+		IFQ_DEQUEUE(&ifp->if_snd, m);
+		if (m == NULL)
+			break;
+		BPF_MTAP(ifp, m);
+
+		/*
+		 * In case the outgoing interface is not usable,
+		 * drop the packet.
+		 */
+		if ((oifp->if_drv_flags & IFF_DRV_RUNNING) == 0 ||
+		    (oifp->if_flags & IFF_UP) ==0) {
+			ifp->if_oerrors++;
+			m_freem(m);
+			continue;
+		}
+		DPRINTF("packet %s -> %s\n", ifp->if_xname, oifp->if_xname);
+
+		/*
+		 * Add a reference so the interface cannot go while the
+		 * packet is in transit as we rely on rcvif to stay valid.
+		 */
+		refcount_acquire(&sc->refcount);
+		m->m_pkthdr.rcvif = oifp;
+		CURVNET_SET_QUIET(oifp->if_vnet);
+		error = netisr_queue(NETISR_EPAIR, m);
+		CURVNET_RESTORE();
+		if (!error) {
+			ifp->if_opackets++;
+			/* Someone else received the packet. */
+			oifp->if_ipackets++;
+		} else {
+			epair_drv_flags |= IFF_DRV_OACTIVE;
+			ifp->if_drv_flags |= IFF_DRV_OACTIVE;
+			ADD_IFQ_FOR_DRAINING(ifp);
+			refcount_release(&sc->refcount);
+		}
+	}
+}
+
+static void
+epair_start(struct ifnet *ifp)
+{
+
+	EPAIR_LOCK();
+	epair_start_locked(ifp);
+	EPAIR_UNLOCK();
+}
+
+static int
+epair_transmit_locked(struct ifnet *ifp, struct mbuf *m)
+{
+	struct epair_softc *sc;
+	struct ifnet *oifp;
+	int error, len;
+	short mflags;
+
+	EPAIR_LOCK_ASSERT();
+	DPRINTF("ifp=%p m=%p\n", ifp, m);
+
+	if (m == NULL)
+		return (0);
+	
+	/*
+	 * We are not going to use the interface en/dequeue mechanism
+	 * on the TX side. We are called from ether_output_frame()
+	 * and will put the packet into the incoming queue of the
+	 * other interface of our pair via the netsir.
+	 */
+	if ((ifp->if_drv_flags & IFF_DRV_RUNNING) == 0) {
+		m_freem(m);
+		return (ENXIO);
+	}
+	if ((ifp->if_flags & IFF_UP) == 0) {
+		m_freem(m);
+		return (ENETDOWN);
+	}
+
+	BPF_MTAP(ifp, m);
+
+	/*
+	 * In case the outgoing interface is not usable,
+	 * drop the packet.
+	 */
+	sc = ifp->if_softc;
+	oifp = sc->oifp;
+	if ((oifp->if_drv_flags & IFF_DRV_RUNNING) == 0 ||
+	    (oifp->if_flags & IFF_UP) ==0) {
+		ifp->if_oerrors++;
+		m_freem(m);
+		return (0);
+	}
+	len = m->m_pkthdr.len;
+	mflags = m->m_flags;
+	DPRINTF("packet %s -> %s\n", ifp->if_xname, oifp->if_xname);
+
+#ifdef ALTQ
+	/* Support ALTQ via the clasic if_start() path. */
+	IF_LOCK(&ifp->if_snd);
+	if (ALTQ_IS_ENABLED(&ifp->if_snd)) {
+		ALTQ_ENQUEUE(&ifp->if_snd, m, NULL, error);
+		if (error)
+			ifp->if_snd.ifq_drops++;
+		IF_UNLOCK(&ifp->if_snd);
+		if (!error) {
+			ifp->if_obytes += len;
+			if (mflags & (M_BCAST|M_MCAST))
+				ifp->if_omcasts++;
+			
+			if ((ifp->if_drv_flags & IFF_DRV_OACTIVE) == 0)
+				epair_start_locked(ifp);
+			else
+				ADD_IFQ_FOR_DRAINING(ifp);
+		}
+		return (error);
+	}
+	IF_UNLOCK(&ifp->if_snd);
+#endif
+
+	if ((epair_drv_flags & IFF_DRV_OACTIVE) != 0) {
+		/*
+		 * Our hardware queue is full, try to fall back
+		 * queuing to the ifq but do not call ifp->if_start.
+		 * Either we are lucky or the packet is gone.
+		 */
+		IFQ_ENQUEUE(&ifp->if_snd, m, error);
+		if (!error)
+			ADD_IFQ_FOR_DRAINING(ifp);
+		return (error);
+	}
+	sc = oifp->if_softc;
+	/*
+	 * Add a reference so the interface cannot go while the
+	 * packet is in transit as we rely on rcvif to stay valid.
+	 */
+	refcount_acquire(&sc->refcount);
+	m->m_pkthdr.rcvif = oifp;
+	CURVNET_SET_QUIET(oifp->if_vnet);
+	error = netisr_queue(NETISR_EPAIR, m);
+	CURVNET_RESTORE();
+	if (!error) {
+		ifp->if_opackets++;
+		/*
+		 * IFQ_HANDOFF_ADJ/ip_handoff() update statistics,
+		 * but as we bypass all this we have to duplicate
+		 * the logic another time.
+		 */
+		ifp->if_obytes += len;
+		if (mflags & (M_BCAST|M_MCAST))
+			ifp->if_omcasts++;
+		/* Someone else received the packet. */
+		oifp->if_ipackets++;
+	} else {
+		/* The packet was freed already. */
+		refcount_release(&sc->refcount);
+		epair_drv_flags |= IFF_DRV_OACTIVE;
+		ifp->if_drv_flags |= IFF_DRV_OACTIVE;
+	}
+
+	return (error);
+}
+
+static int
+epair_transmit(struct ifnet *ifp, struct mbuf *m)
+{
+	int error;
+
+	EPAIR_LOCK();
+	error = epair_transmit_locked(ifp, m);
+	EPAIR_UNLOCK();
+	return (error);
+}
+
+static void
+epair_qflush(struct ifnet *ifp)
+{
+	struct epair_softc *sc;
+	struct ifaltq *ifq;
+	
+	EPAIR_LOCK();
+	sc = ifp->if_softc;
+	ifq = &ifp->if_snd;
+	DPRINTF("ifp=%p sc refcnt=%u ifq_len=%u\n",
+	    ifp, sc->refcount, ifq->ifq_len);
+	/*
+	 * Instead of calling refcount_release(&sc->refcount);
+	 * n times, just subtract for the cleanup.
+	 */
+	sc->refcount -= ifq->ifq_len;
+	EPAIR_UNLOCK();
+	if (sc->if_qflush)
+		sc->if_qflush(ifp);
+}
+
+static int
+epair_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
+{
+	struct ifreq *ifr;
+	int error;
+
+	ifr = (struct ifreq *)data;
+	switch (cmd) {
+	case SIOCSIFFLAGS:
+	case SIOCADDMULTI:
+	case SIOCDELMULTI:
+		error = 0;
+		break;
+
+	default:
+		/* Let the common ethernet handler process this. */
+		error = ether_ioctl(ifp, cmd, data);
+		break;
+	}
+
+	return (error);
+}
+
+static void
+epair_init(void *dummy __unused)
+{
+}
+
+
+/*
+ * Interface cloning functions.
+ * We use our private ones so that we can create/destroy our secondary
+ * device along with the primary one.
+ */
+static int
+epair_clone_match(struct if_clone *ifc, const char *name)
+{
+	const char *cp;
+
+	DPRINTF("name='%s'\n", name);
+
+	/*
+	 * Our base name is epair.
+	 * Our interfaces will be named epair<n>[ab].
+	 * So accept anything of the following list:
+	 * - epair
+	 * - epair<n>
+	 * but not the epair<n>[ab] versions.
+	 */
+	if (strncmp(EPAIRNAME, name, sizeof(EPAIRNAME)-1) != 0)
+		return (0);
+
+	for (cp = name + sizeof(EPAIRNAME) - 1; *cp != '\0'; cp++) {
+		if (*cp < '0' || *cp > '9')
+			return (0);
+	}
+
+	return (1);
+}
+
+static int
+epair_clone_create(struct if_clone *ifc, char *name, size_t len, caddr_t params)
+{
+	struct epair_softc *sca, *scb;
+	struct ifnet *ifp;
+	char *dp;
+	int error, unit, wildcard;
+	uint8_t eaddr[ETHER_ADDR_LEN];	/* 00:00:00:00:00:00 */
+
+	/*
+	 * We are abusing params to create our second interface.
+	 * Actually we already created it and called if_clone_createif()
+	 * for it to do the official insertion procedure the moment we knew
+	 * it cannot fail anymore. So just do attach it here.
+	 */
+	if (params) {
+		scb = (struct epair_softc *)params;
+		ifp = scb->ifp;
+		/* Assign a hopefully unique, locally administered etheraddr. */
+		eaddr[0] = 0x02;
+		eaddr[3] = (ifp->if_index >> 8) & 0xff;
+		eaddr[4] = ifp->if_index & 0xff;
+		eaddr[5] = 0x0b;
+		ether_ifattach(ifp, eaddr);
+		/* Correctly set the name for the cloner list. */
+		strlcpy(name, scb->ifp->if_xname, len);
+		return (0);
+	}
+
+	/* Try to see if a special unit was requested. */
+	error = ifc_name2unit(name, &unit);
+	if (error != 0)
+		return (error);
+	wildcard = (unit < 0);
+
+	error = ifc_alloc_unit(ifc, &unit);
+	if (error != 0)
+		return (error);
+
+	/*
+	 * If no unit had been given, we need to adjust the ifName.
+	 * Also make sure there is space for our extra [ab] suffix.
+	 */
+	for (dp = name; *dp != '\0'; dp++);
+	if (wildcard) {
+		error = snprintf(dp, len - (dp - name), "%d", unit);
+		if (error > len - (dp - name) - 1) {
+			/* ifName too long. */
+			ifc_free_unit(ifc, unit);
+			return (ENOSPC);
+		}
+		dp += error;
+	}
+	if (len - (dp - name) - 1 < 1) {
+		/* No space left for our [ab] suffix. */
+		ifc_free_unit(ifc, unit);
+		return (ENOSPC);
+	}
+	*dp = 'a';
+	/* Must not change dp so we can replace 'a' by 'b' later. */
+	*(dp+1) = '\0';
+
+	/* Allocate memory for both [ab] interfaces */
+	sca = malloc(sizeof(struct epair_softc), M_EPAIR, M_WAITOK | M_ZERO);
+	refcount_init(&sca->refcount, 1);
+	sca->ifp = if_alloc(IFT_ETHER);
+	if (sca->ifp == NULL) {
+		free(sca, M_EPAIR);
+		ifc_free_unit(ifc, unit);
+		return (ENOSPC);
+	}
+
+	scb = malloc(sizeof(struct epair_softc), M_EPAIR, M_WAITOK | M_ZERO);
+	refcount_init(&scb->refcount, 1);
+	scb->ifp = if_alloc(IFT_ETHER);
+	if (scb->ifp == NULL) {
+		free(scb, M_EPAIR);
+		if_free(sca->ifp);
+		free(sca, M_EPAIR);
+		ifc_free_unit(ifc, unit);
+		return (ENOSPC);
+	}
+	
+	/*
+	 * Cross-reference the interfaces so we will be able to free both.
+	 */
+	sca->oifp = scb->ifp;
+	scb->oifp = sca->ifp;
+	
+	/* Finish initialization of interface <n>a. */
+	ifp = sca->ifp;
+	ifp->if_softc = sca;
+	strlcpy(ifp->if_xname, name, IFNAMSIZ);
+	ifp->if_dname = ifc->ifc_name;
+	ifp->if_dunit = unit;
+	ifp->if_flags = IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST;
+	ifp->if_start = epair_start;
+	ifp->if_ioctl = epair_ioctl;
+	ifp->if_init  = epair_init;
+	ifp->if_snd.ifq_maxlen = ifqmaxlen;
+	/* Assign a hopefully unique, locally administered etheraddr. */
+	eaddr[0] = 0x02;
+	eaddr[3] = (ifp->if_index >> 8) & 0xff;
+	eaddr[4] = ifp->if_index & 0xff;
+	eaddr[5] = 0x0a;
+	ether_ifattach(ifp, eaddr);
+	sca->if_qflush = ifp->if_qflush;
+	ifp->if_qflush = epair_qflush;
+	ifp->if_transmit = epair_transmit;
+	ifp->if_baudrate = IF_Gbps(10UL);	/* arbitrary maximum */
+
+	/* Swap the name and finish initialization of interface <n>b. */
+	*dp = 'b';
+
+	ifp = scb->ifp;
+	ifp->if_softc = scb;
+	strlcpy(ifp->if_xname, name, IFNAMSIZ);
+	ifp->if_dname = ifc->ifc_name;
+	ifp->if_dunit = unit;
+	ifp->if_flags = IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST;
+	ifp->if_start = epair_start;
+	ifp->if_ioctl = epair_ioctl;
+	ifp->if_init  = epair_init;
+	ifp->if_snd.ifq_maxlen = ifqmaxlen;
+	/* We need to play some tricks here for the second interface. */
+	strlcpy(name, EPAIRNAME, len);
+	error = if_clone_create(name, len, (caddr_t)scb);
+	if (error)
+		panic("%s: if_clone_createif() for our 2nd iface failed: %d",
+		    __func__, error);
+	scb->if_qflush = ifp->if_qflush;
+	ifp->if_qflush = epair_qflush;
+	ifp->if_transmit = epair_transmit;
+	ifp->if_baudrate = IF_Gbps(10UL);	/* arbitrary maximum */
+
+	/*
+	 * Restore name to <n>a as the ifp for this will go into the
+	 * cloner list for the initial call.
+	 */
+	strlcpy(name, sca->ifp->if_xname, len);
+	DPRINTF("name='%s/%db' created sca=%p scb=%p\n", name, unit, sca, scb);
+
+	/* Tell the world, that we are ready to rock. */
+	sca->ifp->if_drv_flags |= IFF_DRV_RUNNING;
+	scb->ifp->if_drv_flags |= IFF_DRV_RUNNING;
+
+	return (0);
+}
+
+static int
+epair_clone_destroy(struct if_clone *ifc, struct ifnet *ifp)
+{
+	struct ifnet *oifp;
+	struct epair_softc *sca, *scb;
+	int unit, error;
+
+	DPRINTF("ifp=%p\n", ifp);
+
+	/*
+	 * In case we called into if_clone_destroyif() ourselves
+	 * again to remove the second interface, the softc will be
+	 * NULL. In that case so not do anything but return success.
+	 */
+	if (ifp->if_softc == NULL)
+		return (0);
+	
+	unit = ifp->if_dunit;
+	sca = ifp->if_softc;
+	oifp = sca->oifp;
+	scb = oifp->if_softc;
+
+	DPRINTF("ifp=%p oifp=%p\n", ifp, oifp);
+	ifp->if_drv_flags &= ~IFF_DRV_RUNNING;
+	oifp->if_drv_flags &= ~IFF_DRV_RUNNING;
+	ether_ifdetach(oifp);
+	ether_ifdetach(ifp);
+	/*
+	 * Wait for all packets to be dispatched to if_input.
+	 * The numbers can only go down as the interfaces are
+	 * detached so there is no need to use atomics.
+	 */
+	DPRINTF("sca refcnt=%u scb refcnt=%u\n", sca->refcount, scb->refcount);
+	KASSERT(sca->refcount == 1 && scb->refcount == 1,
+	    ("%s: sca->refcount!=1: %d || scb->refcount!=1: %d",
+	    __func__, sca->refcount, scb->refcount));
+
+	/*
+	 * Get rid of our second half.
+	 */
+	oifp->if_softc = NULL;
+	error = if_clone_destroyif(ifc, oifp);
+	if (error)
+		panic("%s: if_clone_destroyif() for our 2nd iface failed: %d",
+		    __func__, error);
+
+	/* Finish cleaning up. Free them and release the unit. */
+	if_free_type(oifp, IFT_ETHER);
+	if_free_type(ifp, IFT_ETHER);
+	free(scb, M_EPAIR);
+	free(sca, M_EPAIR);
+	ifc_free_unit(ifc, unit);
+
+	return (0);
+}
+
+static int
+epair_modevent(module_t mod, int type, void *data)
+{
+	int tmp;
+
+	switch (type) {
+	case MOD_LOAD:
+		/* For now limit us to one global mutex and one inq. */
+		EPAIR_LOCK_INIT();
+		epair_drv_flags = 0;
+		epairinq.ifq_maxlen = 16 * ifqmaxlen; /* What is a good 16? */
+		if (TUNABLE_INT_FETCH("net.link.epair.netisr_maxqlen", &tmp))
+		    epairinq.ifq_maxlen = tmp;
+		mtx_init(&epairinq.ifq_mtx, "epair_inq", NULL, MTX_DEF);
+		netisr_register2(NETISR_EPAIR, (netisr_t *)epair_sintr,
+		    epair_sintr_drained, &epairinq, 0);
+		if_clone_attach(&epair_cloner);
+		if (bootverbose)
+			printf("%s initialized.\n", EPAIRNAME);
+		break;
+	case MOD_UNLOAD:
+		if_clone_detach(&epair_cloner);
+		netisr_unregister(NETISR_EPAIR);
+		mtx_destroy(&epairinq.ifq_mtx);
+		EPAIR_LOCK_DESTROY();
+		if (bootverbose)
+			printf("%s unloaded.\n", EPAIRNAME);
+		break;
+	default:
+		return (EOPNOTSUPP);
+	}
+	return (0);
+}
+
+static moduledata_t epair_mod = {
+	"if_epair",
+	epair_modevent,
+	0
+};
+
+DECLARE_MODULE(if_epair, epair_mod, SI_SUB_PSEUDO, SI_ORDER_ANY);
+MODULE_VERSION(if_epair, 1);