/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2008 The FreeBSD Foundation
 * Copyright (c) 2009-2021 Bjoern A. Zeeb <bz@FreeBSD.org>
 *
 * 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 back-to-back connected ethernet like interfaces
 * (``two interfaces with a virtual cross-over cable'').
 *
 * This is mostly intended to be used to provide connectivity between
 * different virtual network stack instances.
 */

#include <sys/cdefs.h>
#include "opt_rss.h"
#include "opt_inet.h"
#include "opt_inet6.h"

#include <sys/param.h>
#include <sys/bus.h>
#include <sys/hash.h>
#include <sys/interrupt.h>
#include <sys/jail.h>
#include <sys/kernel.h>
#include <sys/libkern.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/module.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/sched.h>
#include <sys/smp.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/sysctl.h>
#include <sys/taskqueue.h>

#include <net/bpf.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/if_clone.h>
#include <net/if_media.h>
#include <net/if_private.h>
#include <net/if_types.h>
#include <net/if_vlan_var.h>
#include <net/netisr.h>
#ifdef RSS
#include <net/rss_config.h>
#ifdef INET
#include <netinet/in_rss.h>
#endif
#ifdef INET6
#include <netinet6/in6_rss.h>
#endif
#endif
#include <net/vnet.h>

static const char epairname[] = "epair";
#define RXRSIZE 4096    /* Probably overkill by 4-8x. */

static MALLOC_DEFINE(M_EPAIR, epairname,
    "Pair of virtual cross-over connected Ethernet-like interfaces");

VNET_DEFINE_STATIC(struct if_clone *, epair_cloner);
#define V_epair_cloner  VNET(epair_cloner)

static unsigned int next_index = 0;
#define EPAIR_LOCK_INIT()               mtx_init(&epair_n_index_mtx, "epairidx", \
                                            NULL, MTX_DEF)
#define EPAIR_LOCK_DESTROY()            mtx_destroy(&epair_n_index_mtx)
#define EPAIR_LOCK()                    mtx_lock(&epair_n_index_mtx)
#define EPAIR_UNLOCK()                  mtx_unlock(&epair_n_index_mtx)

SYSCTL_DECL(_net_link);
static SYSCTL_NODE(_net_link, OID_AUTO, epair, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
        "Pair of virtual cross-over connected Ethernet-like interfaces");

static bool use_ether_gen_addr = true;
SYSCTL_BOOL(_net_link_epair, OID_AUTO, ether_gen_addr, CTLFLAG_RWTUN,
        &use_ether_gen_addr, false,
        "Generate MAC with FreeBSD OUI using ether_gen_addr(9)");

struct epair_softc;
struct epair_queue {
        struct mtx               mtx;
        struct mbufq             q;
        int                      id;
        enum {
                EPAIR_QUEUE_IDLE,
                EPAIR_QUEUE_WAKING,
                EPAIR_QUEUE_RUNNING,
        }                        state;
        struct task              tx_task;
        struct epair_softc      *sc;
};

static struct mtx epair_n_index_mtx;
struct epair_softc {
        struct ifnet            *ifp;           /* This ifp. */
        struct ifnet            *oifp;          /* other ifp of pair. */
        int                      num_queues;
        struct epair_queue      *queues;
        struct ifmedia           media;         /* Media config (fake). */
        STAILQ_ENTRY(epair_softc) entry;
};

struct epair_tasks_t {
        int                      tasks;
        struct taskqueue         *tq[MAXCPU];
};

static struct epair_tasks_t epair_tasks;

static void
epair_clear_mbuf(struct mbuf *m)
{
        M_ASSERTPKTHDR(m);

        /* Remove any CSUM_SND_TAG as ether_input will barf. */
        if (m->m_pkthdr.csum_flags & CSUM_SND_TAG) {
                m_snd_tag_rele(m->m_pkthdr.snd_tag);
                m->m_pkthdr.snd_tag = NULL;
                m->m_pkthdr.csum_flags &= ~CSUM_SND_TAG;
        }

        m_tag_delete_nonpersistent(m);
}

static void
epair_tx_start_deferred(void *arg, int pending)
{
        struct epair_queue *q = (struct epair_queue *)arg;
        if_t ifp;
        struct mbuf *m, *n;
        bool resched;

        ifp = q->sc->ifp;

        if_ref(ifp);
        CURVNET_SET(ifp->if_vnet);

        mtx_lock(&q->mtx);
        m = mbufq_flush(&q->q);
        q->state = EPAIR_QUEUE_RUNNING;
        mtx_unlock(&q->mtx);

        while (m != NULL) {
                n = STAILQ_NEXT(m, m_stailqpkt);
                m->m_nextpkt = NULL;
                if_input(ifp, m);
                m = n;
        }

        /*
         * Avoid flushing the queue more than once per task.  We can otherwise
         * end up starving ourselves in a multi-epair routing configuration.
         */
        mtx_lock(&q->mtx);
        if (!mbufq_empty(&q->q)) {
                resched = true;
                q->state = EPAIR_QUEUE_WAKING;
        } else {
                resched = false;
                q->state = EPAIR_QUEUE_IDLE;
        }
        mtx_unlock(&q->mtx);

        if (resched)
                taskqueue_enqueue(epair_tasks.tq[q->id], &q->tx_task);

        CURVNET_RESTORE();
        if_rele(ifp);
}

static struct epair_queue *
epair_select_queue(struct epair_softc *sc, struct mbuf *m)
{
        uint32_t bucket;
#ifdef RSS
        struct ether_header *eh;
        int ret;

        ret = rss_m2bucket(m, &bucket);
        if (ret) {
                /* Actually hash the packet. */
                eh = mtod(m, struct ether_header *);

                switch (ntohs(eh->ether_type)) {
#ifdef INET
                case ETHERTYPE_IP:
                        rss_soft_m2cpuid_v4(m, 0, &bucket);
                        break;
#endif
#ifdef INET6
                case ETHERTYPE_IPV6:
                        rss_soft_m2cpuid_v6(m, 0, &bucket);
                        break;
#endif
                default:
                        bucket = 0;
                        break;
                }
        }
        bucket %= sc->num_queues;
#else
        bucket = 0;
#endif
        return (&sc->queues[bucket]);
}

static void
epair_prepare_mbuf(struct mbuf *m, struct ifnet *src_ifp)
{
        M_ASSERTPKTHDR(m);
        epair_clear_mbuf(m);
        if_setrcvif(m, src_ifp);
        M_SETFIB(m, src_ifp->if_fib);

        MPASS(m->m_nextpkt == NULL);
        MPASS((m->m_pkthdr.csum_flags & CSUM_SND_TAG) == 0);
}

static void
epair_menq(struct mbuf *m, struct epair_softc *osc)
{
        struct epair_queue *q;
        struct ifnet *ifp, *oifp;
        int error, len;
        bool mcast;

        /*
         * I know this looks weird. We pass the "other sc" as we need that one
         * and can get both ifps from it as well.
         */
        oifp = osc->ifp;
        ifp = osc->oifp;

        epair_prepare_mbuf(m, oifp);

        /* Save values as once the mbuf is queued, it's not ours anymore. */
        len = m->m_pkthdr.len;
        mcast = (m->m_flags & (M_BCAST | M_MCAST)) != 0;

        q = epair_select_queue(osc, m);

        mtx_lock(&q->mtx);
        if (q->state == EPAIR_QUEUE_IDLE) {
                q->state = EPAIR_QUEUE_WAKING;
                taskqueue_enqueue(epair_tasks.tq[q->id], &q->tx_task);
        }
        error = mbufq_enqueue(&q->q, m);
        mtx_unlock(&q->mtx);

        if (error != 0) {
                m_freem(m);
                if_inc_counter(ifp, IFCOUNTER_OQDROPS, 1);
        } else {
                if_inc_counter(ifp, IFCOUNTER_OPACKETS, 1);
                if_inc_counter(ifp, IFCOUNTER_OBYTES, len);
                if (mcast)
                        if_inc_counter(ifp, IFCOUNTER_OMCASTS, 1);
                if_inc_counter(oifp, IFCOUNTER_IPACKETS, 1);
        }
}

static void
epair_start(struct ifnet *ifp)
{
        struct mbuf *m;
        struct epair_softc *sc;
        struct ifnet *oifp;

        /*
         * We get packets here from ether_output via if_handoff()
         * and need to put them into the input queue of the oifp
         * and will put the packet into the receive-queue (rxq) of the
         * other interface (oifp) of our pair.
         */
        sc = ifp->if_softc;
        oifp = sc->oifp;
        sc = oifp->if_softc;
        for (;;) {
                IFQ_DEQUEUE(&ifp->if_snd, m);
                if (m == NULL)
                        break;
                M_ASSERTPKTHDR(m);
                BPF_MTAP(ifp, m);

                /* In case either interface is not usable drop the packet. */
                if ((ifp->if_drv_flags & IFF_DRV_RUNNING) == 0 ||
                    (ifp->if_flags & IFF_UP) == 0 ||
                    (oifp->if_drv_flags & IFF_DRV_RUNNING) == 0 ||
                    (oifp->if_flags & IFF_UP) == 0) {
                        m_freem(m);
                        continue;
                }

                epair_menq(m, sc);
        }
}

static int
epair_transmit(struct ifnet *ifp, struct mbuf *m)
{
        struct epair_softc *sc;
        struct ifnet *oifp;
#ifdef ALTQ
        int len;
        bool mcast;
#endif

        if (m == NULL)
                return (0);
        M_ASSERTPKTHDR(m);

        /*
         * We could just transmit this, but it makes testing easier if we're a
         * little bit more like real hardware.
         * Allow just that little bit extra for ethernet (and vlan) headers.
         */
        if (m->m_pkthdr.len > (ifp->if_mtu + sizeof(struct ether_vlan_header))) {
                m_freem(m);
                if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
                return (E2BIG);
        }

        /*
         * 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 receive-queue (rxq) of the
         * other interface (oifp) of our pair.
         */
        if ((ifp->if_drv_flags & IFF_DRV_RUNNING) == 0) {
                m_freem(m);
                if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
                return (ENXIO);
        }
        if ((ifp->if_flags & IFF_UP) == 0) {
                m_freem(m);
                if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
                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) {
                if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
                m_freem(m);
                return (0);
        }

#ifdef ALTQ
        len = m->m_pkthdr.len;
        mcast = (m->m_flags & (M_BCAST | M_MCAST)) != 0;
        int error = 0;

        /* Support ALTQ via the classic 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)
                        if_inc_counter(ifp, IFCOUNTER_OQDROPS, 1);
                IF_UNLOCK(&ifp->if_snd);
                if (!error) {
                        if_inc_counter(ifp, IFCOUNTER_OBYTES, len);
                        if (mcast)
                                if_inc_counter(ifp, IFCOUNTER_OMCASTS, 1);
                        epair_start(ifp);
                }
                return (error);
        }
        IF_UNLOCK(&ifp->if_snd);
#endif

        epair_menq(m, oifp->if_softc);
        return (0);
}

static void
epair_qflush(struct ifnet *ifp __unused)
{
}

static int
epair_media_change(struct ifnet *ifp __unused)
{

        /* Do nothing. */
        return (0);
}

static void
epair_media_status(struct ifnet *ifp __unused, struct ifmediareq *imr)
{

        imr->ifm_status = IFM_AVALID | IFM_ACTIVE;
        imr->ifm_active = IFM_ETHER | IFM_10G_T | IFM_FDX;
}

/*
 * Update ifp->if_hwassist according to the current value of ifp->if_capenable.
 */
static void
epair_caps_changed(struct ifnet *ifp)
{
        uint64_t hwassist = 0;

        if (ifp->if_capenable & IFCAP_TXCSUM)
                hwassist |= CSUM_IP_TCP | CSUM_IP_UDP;
        if (ifp->if_capenable & IFCAP_TXCSUM_IPV6)
                hwassist |= CSUM_IP6_TCP | CSUM_IP6_UDP;
        ifp->if_hwassist = hwassist;
}

static int
epair_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
{
        struct epair_softc *sc;
        struct ifreq *ifr;
        int error;

        ifr = (struct ifreq *)data;
        switch (cmd) {
        case SIOCSIFFLAGS:
        case SIOCADDMULTI:
        case SIOCDELMULTI:
                error = 0;
                break;

        case SIOCSIFMEDIA:
        case SIOCGIFMEDIA:
                sc = ifp->if_softc;
                error = ifmedia_ioctl(ifp, ifr, &sc->media, cmd);
                break;

        case SIOCSIFMTU:
                /* We basically allow all kinds of MTUs. */
                ifp->if_mtu = ifr->ifr_mtu;
                error = 0;
                break;

        case SIOCGIFCAP:
                ifr->ifr_reqcap = ifp->if_capabilities;
                ifr->ifr_curcap = ifp->if_capenable;
                error = 0;
                break;
        case SIOCSIFCAP:
                /*
                 * Enable/disable capabilities as requested, besides
                 * IFCAP_RXCSUM(_IPV6), which always remain enabled.
                 * Incoming packets may have the mbuf flag CSUM_DATA_VALID set.
                 * Without IFCAP_RXCSUM(_IPV6), this flag would have to be
                 * removed, which does not seem helpful.
                 */
                ifp->if_capenable = ifr->ifr_reqcap | IFCAP_RXCSUM |
                    IFCAP_RXCSUM_IPV6;
                epair_caps_changed(ifp);
                VLAN_CAPABILITIES(ifp);
                /*
                 * If IFCAP_TXCSUM(_IPV6) has been changed, change it on the
                 * other epair interface as well.
                 * A bridge disables IFCAP_TXCSUM(_IPV6) when adding one epair
                 * interface if another interface in the bridge has it disabled.
                 * In that case this capability needs to be disabled on the
                 * other epair interface to avoid sending packets in the bridge
                 * that rely on this capability.
                 * Do the same for IFCAP_VLAN_HWTAGGING. If the sending epair
                 * end has this capability enabled, the other end has to have
                 * it enabled too. Otherwise, epair would have to add the VLAN
                 * tag in the Ethernet header.
                 */
                sc = ifp->if_softc;
                if ((ifp->if_capenable ^ sc->oifp->if_capenable) &
                    (IFCAP_TXCSUM | IFCAP_TXCSUM_IPV6 | IFCAP_VLAN_HWTAGGING)) {
                        sc->oifp->if_capenable &=
                            ~(IFCAP_TXCSUM | IFCAP_TXCSUM_IPV6 |
                              IFCAP_VLAN_HWTAGGING);
                        sc->oifp->if_capenable |= ifp->if_capenable &
                            (IFCAP_TXCSUM | IFCAP_TXCSUM_IPV6 |
                             IFCAP_VLAN_HWTAGGING);
                        epair_caps_changed(sc->oifp);
                        VLAN_CAPABILITIES(sc->oifp);
                }
                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;

        /*
         * 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 void
epair_generate_mac_byname(struct epair_softc *sc, uint8_t eaddr[])
{
        struct ether_addr gen_eaddr;
        int i;

        ether_gen_addr_byname(if_name(sc->ifp), &gen_eaddr);
        for (i = 0; i < ETHER_ADDR_LEN; i++)
                eaddr[i] = gen_eaddr.octet[i];
}

static void
epair_clone_add(struct if_clone *ifc, struct epair_softc *scb)
{
        struct ifnet *ifp;
        uint8_t eaddr[ETHER_ADDR_LEN];  /* 00:00:00:00:00:00 */

        ifp = scb->ifp;
        if (!use_ether_gen_addr) {
                /* Copy epairNa etheraddr and change the last byte. */
                memcpy(eaddr, scb->oifp->if_hw_addr, ETHER_ADDR_LEN);
                eaddr[5] = 0x0b;
        } else
                epair_generate_mac_byname(scb, eaddr);
        ether_ifattach(ifp, eaddr);

        if_clone_addif(ifc, ifp);
}

static struct epair_softc *
epair_alloc_sc(struct if_clone *ifc)
{
        struct epair_softc *sc;

        struct ifnet *ifp = if_alloc(IFT_ETHER);
        sc = malloc(sizeof(struct epair_softc), M_EPAIR, M_WAITOK | M_ZERO);
        sc->ifp = ifp;
        sc->num_queues = epair_tasks.tasks;
        sc->queues = mallocarray(sc->num_queues, sizeof(struct epair_queue),
            M_EPAIR, M_WAITOK);
        for (int i = 0; i < sc->num_queues; i++) {
                struct epair_queue *q = &sc->queues[i];
                q->id = i;
                q->state = EPAIR_QUEUE_IDLE;
                mtx_init(&q->mtx, "epairq", NULL, MTX_DEF | MTX_NEW);
                mbufq_init(&q->q, RXRSIZE);
                q->sc = sc;
                NET_TASK_INIT(&q->tx_task, 0, epair_tx_start_deferred, q);
        }

        /* Initialise pseudo media types. */
        ifmedia_init(&sc->media, 0, epair_media_change, epair_media_status);
        ifmedia_add(&sc->media, IFM_ETHER | IFM_10G_T, 0, NULL);
        ifmedia_set(&sc->media, IFM_ETHER | IFM_10G_T);

        return (sc);
}

static void
epair_setup_ifp(struct epair_softc *sc, char *name, int unit)
{
        struct ifnet *ifp = sc->ifp;

        ifp->if_softc = sc;
        strlcpy(ifp->if_xname, name, IFNAMSIZ);
        ifp->if_dname = epairname;
        ifp->if_dunit = unit;
        ifp->if_flags = IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST;
        ifp->if_capabilities =
            IFCAP_VLAN_MTU | IFCAP_VLAN_HWTAGGING |
            IFCAP_TXCSUM | IFCAP_RXCSUM |
            IFCAP_TXCSUM_IPV6 | IFCAP_RXCSUM_IPV6;
        ifp->if_capenable = ifp->if_capabilities;
        epair_caps_changed(ifp);
        ifp->if_transmit = epair_transmit;
        ifp->if_qflush = epair_qflush;
        ifp->if_start = epair_start;
        ifp->if_ioctl = epair_ioctl;
        ifp->if_init  = epair_init;
        if_setsendqlen(ifp, ifqmaxlen);
        if_setsendqready(ifp);

        ifp->if_baudrate = IF_Gbps(10); /* arbitrary maximum */
}

static void
epair_generate_mac(struct epair_softc *sc, uint8_t *eaddr)
{
        uint32_t key[3];
        uint32_t hash;
        uint64_t hostid;

        EPAIR_LOCK();
#ifdef SMP
        /* Get an approximate distribution. */
        hash = next_index % mp_ncpus;
#else
        hash = 0;
#endif
        EPAIR_UNLOCK();

        /*
         * Calculate the etheraddr hashing the hostid and the
         * interface index. The result would be hopefully unique.
         * Note that the "a" component of an epair instance may get moved
         * to a different VNET after creation. In that case its index
         * will be freed and the index can get reused by new epair instance.
         * Make sure we do not create same etheraddr again.
         */
        getcredhostid(curthread->td_ucred, (unsigned long *)&hostid);
        if (hostid == 0)
                arc4rand(&hostid, sizeof(hostid), 0);

        struct ifnet *ifp = sc->ifp;
        EPAIR_LOCK();
        if (ifp->if_index > next_index)
                next_index = ifp->if_index;
        else
                next_index++;

        key[0] = (uint32_t)next_index;
        EPAIR_UNLOCK();
        key[1] = (uint32_t)(hostid & 0xffffffff);
        key[2] = (uint32_t)((hostid >> 32) & 0xfffffffff);
        hash = jenkins_hash32(key, 3, 0);

        eaddr[0] = 0x02;
        memcpy(&eaddr[1], &hash, 4);
        eaddr[5] = 0x0a;
}

static void
epair_free_sc(struct epair_softc *sc)
{

        if_free(sc->ifp);
        ifmedia_removeall(&sc->media);
        for (int i = 0; i < sc->num_queues; i++) {
                struct epair_queue *q = &sc->queues[i];
                mtx_destroy(&q->mtx);
        }
        free(sc->queues, M_EPAIR);
        free(sc, M_EPAIR);
}

static void
epair_set_state(struct ifnet *ifp, bool running)
{
        if (running) {
                ifp->if_drv_flags |= IFF_DRV_RUNNING;
                if_link_state_change(ifp, LINK_STATE_UP);
        } else {
                if_link_state_change(ifp, LINK_STATE_DOWN);
                ifp->if_drv_flags &= ~IFF_DRV_RUNNING;
        }
}

static int
epair_handle_unit(struct if_clone *ifc, char *name, size_t len, int *punit)
{
        int error = 0, unit, wildcard;
        char *dp;

        /* 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) {
                int slen = snprintf(dp, len - (dp - name), "%d", unit);
                if (slen > len - (dp - name) - 1) {
                        /* ifName too long. */
                        error = ENOSPC;
                        goto done;
                }
                dp += slen;
        }
        if (len - (dp - name) - 1 < 1) {
                /* No space left for our [ab] suffix. */
                error = ENOSPC;
                goto done;
        }
        *dp = 'b';
        /* Must not change dp so we can replace 'a' by 'b' later. */
        *(dp+1) = '\0';

        /* Check if 'a' and 'b' interfaces already exist. */ 
        if (ifunit(name) != NULL) {
                error = EEXIST;
                goto done;
        }

        *dp = 'a';
        if (ifunit(name) != NULL) {
                error = EEXIST;
                goto done;
        }
        *punit = unit;
done:
        if (error != 0)
                ifc_free_unit(ifc, unit);

        return (error);
}

static int
epair_clone_create(struct if_clone *ifc, char *name, size_t len,
    struct ifc_data *ifd, struct ifnet **ifpp)
{
        struct epair_softc *sca, *scb;
        struct ifnet *ifp;
        char *dp;
        int error, unit;
        uint8_t eaddr[ETHER_ADDR_LEN];  /* 00:00:00:00:00:00 */

        error = epair_handle_unit(ifc, name, len, &unit);
        if (error != 0)
                return (error);

        /* Allocate memory for both [ab] interfaces */
        sca = epair_alloc_sc(ifc);
        scb = epair_alloc_sc(ifc);

        /*
         * 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;
        epair_setup_ifp(sca, name, unit);
        if (!use_ether_gen_addr)
                epair_generate_mac(sca, eaddr);
        else
                epair_generate_mac_byname(sca, eaddr);

        ether_ifattach(ifp, eaddr);

        /* Swap the name and finish initialization of interface <n>b. */
        dp = name + strlen(name) - 1;
        *dp = 'b';

        epair_setup_ifp(scb, name, unit);

        ifp = scb->ifp;
        /* We need to play some tricks here for the second interface. */
        strlcpy(name, epairname, len);
        /* Correctly set the name for the cloner list. */
        strlcpy(name, scb->ifp->if_xname, len);

        epair_clone_add(ifc, scb);

        /*
         * 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);

        /* Tell the world, that we are ready to rock. */
        epair_set_state(sca->ifp, true);
        epair_set_state(scb->ifp, true);

        *ifpp = sca->ifp;

        return (0);
}

static void
epair_drain_rings(struct epair_softc *sc)
{
        for (int i = 0; i < sc->num_queues; i++) {
                struct epair_queue *q;
                struct mbuf *m, *n;

                q = &sc->queues[i];
                mtx_lock(&q->mtx);
                m = mbufq_flush(&q->q);
                mtx_unlock(&q->mtx);

                for (; m != NULL; m = n) {
                        n = m->m_nextpkt;
                        m_freem(m);
                }
        }
}

static int
epair_clone_destroy(struct if_clone *ifc, struct ifnet *ifp, uint32_t flags)
{
        struct ifnet *oifp;
        struct epair_softc *sca, *scb;
        int unit, error;

        /*
         * 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;

        /* Frist get the interfaces down and detached. */
        epair_set_state(ifp, false);
        epair_set_state(oifp, false);

        ether_ifdetach(ifp);
        ether_ifdetach(oifp);

        /* Third free any queued packets and all the resources. */
        CURVNET_SET_QUIET(oifp->if_vnet);
        epair_drain_rings(scb);
        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);
        epair_free_sc(scb);
        CURVNET_RESTORE();

        epair_drain_rings(sca);
        epair_free_sc(sca);

        /* Last free the cloner unit. */
        ifc_free_unit(ifc, unit);

        return (0);
}

static void
vnet_epair_init(const void *unused __unused)
{
        struct if_clone_addreq req = {
                .match_f = epair_clone_match,
                .create_f = epair_clone_create,
                .destroy_f = epair_clone_destroy,
        };
        V_epair_cloner = ifc_attach_cloner(epairname, &req);
}
VNET_SYSINIT(vnet_epair_init, SI_SUB_PSEUDO, SI_ORDER_ANY,
    vnet_epair_init, NULL);

static void
vnet_epair_uninit(const void *unused __unused)
{

        ifc_detach_cloner(V_epair_cloner);
}
VNET_SYSUNINIT(vnet_epair_uninit, SI_SUB_INIT_IF, SI_ORDER_ANY,
    vnet_epair_uninit, NULL);

static int
epair_mod_init(void)
{
        char name[32];
        epair_tasks.tasks = 0;

#ifdef RSS
        int cpu;

        CPU_FOREACH(cpu) {
                cpuset_t cpu_mask;

                /* Pin to this CPU so we get appropriate NUMA allocations. */
                thread_lock(curthread);
                sched_bind(curthread, cpu);
                thread_unlock(curthread);

                snprintf(name, sizeof(name), "epair_task_%d", cpu);

                epair_tasks.tq[cpu] = taskqueue_create(name, M_WAITOK,
                    taskqueue_thread_enqueue,
                    &epair_tasks.tq[cpu]);
                CPU_SETOF(cpu, &cpu_mask);
                taskqueue_start_threads_cpuset(&epair_tasks.tq[cpu], 1, PI_NET,
                    &cpu_mask, "%s", name);

                epair_tasks.tasks++;
        }
        thread_lock(curthread);
        sched_unbind(curthread);
        thread_unlock(curthread);
#else
        snprintf(name, sizeof(name), "epair_task");

        epair_tasks.tq[0] = taskqueue_create(name, M_WAITOK,
            taskqueue_thread_enqueue,
            &epair_tasks.tq[0]);
        taskqueue_start_threads(&epair_tasks.tq[0], 1, PI_NET, "%s", name);

        epair_tasks.tasks = 1;
#endif

        return (0);
}

static void
epair_mod_cleanup(void)
{

        for (int i = 0; i < epair_tasks.tasks; i++) {
                taskqueue_drain_all(epair_tasks.tq[i]);
                taskqueue_free(epair_tasks.tq[i]);
        }
}

static int
epair_modevent(module_t mod, int type, void *data)
{
        int ret;

        switch (type) {
        case MOD_LOAD:
                EPAIR_LOCK_INIT();
                ret = epair_mod_init();
                if (ret != 0)
                        return (ret);
                if (bootverbose)
                        printf("%s: %s initialized.\n", __func__, epairname);
                break;
        case MOD_UNLOAD:
                epair_mod_cleanup();
                EPAIR_LOCK_DESTROY();
                if (bootverbose)
                        printf("%s: %s unloaded.\n", __func__, 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_MIDDLE);
MODULE_VERSION(if_epair, 3);