[apple/xnu.git] / bsd / netinet6 / mld6.c

/*
 * Copyright (c) 2000-2019 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*-
 * Copyright (c) 2009 Bruce Simpson.
 *
 * 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.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * 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.
 */

/*
 * Copyright (c) 1988 Stephen Deering.
 * Copyright (c) 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Stephen Deering of Stanford University.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      @(#)igmp.c      8.1 (Berkeley) 7/19/93
 */
/*
 * NOTICE: This file was modified by SPARTA, Inc. in 2005 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 */

#include <sys/cdefs.h>

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/protosw.h>
#include <sys/sysctl.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/mcache.h>

#include <dev/random/randomdev.h>

#include <kern/zalloc.h>

#include <net/if.h>
#include <net/route.h>

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet6/in6_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <netinet/icmp6.h>
#include <netinet6/mld6.h>
#include <netinet6/mld6_var.h>

/* Lock group and attribute for mld_mtx */
static lck_attr_t       *mld_mtx_attr;
static lck_grp_t        *mld_mtx_grp;
static lck_grp_attr_t   *mld_mtx_grp_attr;

/*
 * Locking and reference counting:
 *
 * mld_mtx mainly protects mli_head.  In cases where both mld_mtx and
 * in6_multihead_lock must be held, the former must be acquired first in order
 * to maintain lock ordering.  It is not a requirement that mld_mtx be
 * acquired first before in6_multihead_lock, but in case both must be acquired
 * in succession, the correct lock ordering must be followed.
 *
 * Instead of walking the if_multiaddrs list at the interface and returning
 * the ifma_protospec value of a matching entry, we search the global list
 * of in6_multi records and find it that way; this is done with in6_multihead
 * lock held.  Doing so avoids the race condition issues that many other BSDs
 * suffer from (therefore in our implementation, ifma_protospec will never be
 * NULL for as long as the in6_multi is valid.)
 *
 * The above creates a requirement for the in6_multi to stay in in6_multihead
 * list even after the final MLD leave (in MLDv2 mode) until no longer needs
 * be retransmitted (this is not required for MLDv1.)  In order to handle
 * this, the request and reference counts of the in6_multi are bumped up when
 * the state changes to MLD_LEAVING_MEMBER, and later dropped in the timeout
 * handler.  Each in6_multi holds a reference to the underlying mld_ifinfo.
 *
 * Thus, the permitted lock order is:
 *
 *      mld_mtx, in6_multihead_lock, inm6_lock, mli_lock
 *
 * Any may be taken independently, but if any are held at the same time,
 * the above lock order must be followed.
 */
static decl_lck_mtx_data(, mld_mtx);

SLIST_HEAD(mld_in6m_relhead, in6_multi);

static void     mli_initvar(struct mld_ifinfo *, struct ifnet *, int);
static struct mld_ifinfo *mli_alloc(int);
static void     mli_free(struct mld_ifinfo *);
static void     mli_delete(const struct ifnet *, struct mld_in6m_relhead *);
static void     mld_dispatch_packet(struct mbuf *);
static void     mld_final_leave(struct in6_multi *, struct mld_ifinfo *,
    struct mld_tparams *);
static int      mld_handle_state_change(struct in6_multi *, struct mld_ifinfo *,
    struct mld_tparams *);
static int      mld_initial_join(struct in6_multi *, struct mld_ifinfo *,
    struct mld_tparams *, const int);
#ifdef MLD_DEBUG
static const char *     mld_rec_type_to_str(const int);
#endif
static uint32_t mld_set_version(struct mld_ifinfo *, const int);
static void     mld_flush_relq(struct mld_ifinfo *, struct mld_in6m_relhead *);
static void     mld_dispatch_queue_locked(struct mld_ifinfo *, struct ifqueue *, int);
static int      mld_v1_input_query(struct ifnet *, const struct ip6_hdr *,
    /*const*/ struct mld_hdr *);
static int      mld_v1_input_report(struct ifnet *, struct mbuf *,
    const struct ip6_hdr *, /*const*/ struct mld_hdr *);
static void     mld_v1_process_group_timer(struct in6_multi *, const int);
static void     mld_v1_process_querier_timers(struct mld_ifinfo *);
static int      mld_v1_transmit_report(struct in6_multi *, const int);
static uint32_t mld_v1_update_group(struct in6_multi *, const int);
static void     mld_v2_cancel_link_timers(struct mld_ifinfo *);
static uint32_t mld_v2_dispatch_general_query(struct mld_ifinfo *);
static struct mbuf *
mld_v2_encap_report(struct ifnet *, struct mbuf *);
static int      mld_v2_enqueue_filter_change(struct ifqueue *,
    struct in6_multi *);
static int      mld_v2_enqueue_group_record(struct ifqueue *,
    struct in6_multi *, const int, const int, const int,
    const int);
static int      mld_v2_input_query(struct ifnet *, const struct ip6_hdr *,
    struct mbuf *, const int, const int);
static int      mld_v2_merge_state_changes(struct in6_multi *,
    struct ifqueue *);
static void     mld_v2_process_group_timers(struct mld_ifinfo *,
    struct ifqueue *, struct ifqueue *,
    struct in6_multi *, const int);
static int      mld_v2_process_group_query(struct in6_multi *,
    int, struct mbuf *, const int);
static int      sysctl_mld_gsr SYSCTL_HANDLER_ARGS;
static int      sysctl_mld_ifinfo SYSCTL_HANDLER_ARGS;
static int      sysctl_mld_v2enable SYSCTL_HANDLER_ARGS;

static int mld_timeout_run;             /* MLD timer is scheduled to run */
static void mld_timeout(void *);
static void mld_sched_timeout(void);

/*
 * Normative references: RFC 2710, RFC 3590, RFC 3810.
 */
static struct timeval mld_gsrdelay = {.tv_sec = 10, .tv_usec = 0};
static LIST_HEAD(, mld_ifinfo) mli_head;

static int querier_present_timers_running6;
static int interface_timers_running6;
static int state_change_timers_running6;
static int current_state_timers_running6;

static unsigned int mld_mli_list_genid;
/*
 * Subsystem lock macros.
 */
#define MLD_LOCK()                      \
        lck_mtx_lock(&mld_mtx)
#define MLD_LOCK_ASSERT_HELD()          \
        LCK_MTX_ASSERT(&mld_mtx, LCK_MTX_ASSERT_OWNED)
#define MLD_LOCK_ASSERT_NOTHELD()       \
        LCK_MTX_ASSERT(&mld_mtx, LCK_MTX_ASSERT_NOTOWNED)
#define MLD_UNLOCK()                    \
        lck_mtx_unlock(&mld_mtx)

#define MLD_ADD_DETACHED_IN6M(_head, _in6m) {                           \
        SLIST_INSERT_HEAD(_head, _in6m, in6m_dtle);                     \
}

#define MLD_REMOVE_DETACHED_IN6M(_head) {                               \
        struct in6_multi *_in6m, *_inm_tmp;                             \
        SLIST_FOREACH_SAFE(_in6m, _head, in6m_dtle, _inm_tmp) {         \
                SLIST_REMOVE(_head, _in6m, in6_multi, in6m_dtle);       \
                IN6M_REMREF(_in6m);                                     \
        }                                                               \
        VERIFY(SLIST_EMPTY(_head));                                     \
}

#define MLI_ZONE_MAX            64              /* maximum elements in zone */
#define MLI_ZONE_NAME           "mld_ifinfo"    /* zone name */

static unsigned int mli_size;                   /* size of zone element */
static struct zone *mli_zone;                   /* zone for mld_ifinfo */

SYSCTL_DECL(_net_inet6);        /* Note: Not in any common header. */

SYSCTL_NODE(_net_inet6, OID_AUTO, mld, CTLFLAG_RW | CTLFLAG_LOCKED, 0,
    "IPv6 Multicast Listener Discovery");
SYSCTL_PROC(_net_inet6_mld, OID_AUTO, gsrdelay,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
    &mld_gsrdelay.tv_sec, 0, sysctl_mld_gsr, "I",
    "Rate limit for MLDv2 Group-and-Source queries in seconds");

SYSCTL_NODE(_net_inet6_mld, OID_AUTO, ifinfo, CTLFLAG_RD | CTLFLAG_LOCKED,
    sysctl_mld_ifinfo, "Per-interface MLDv2 state");

static int      mld_v1enable = 1;
SYSCTL_INT(_net_inet6_mld, OID_AUTO, v1enable, CTLFLAG_RW | CTLFLAG_LOCKED,
    &mld_v1enable, 0, "Enable fallback to MLDv1");

static int      mld_v2enable = 1;
SYSCTL_PROC(_net_inet6_mld, OID_AUTO, v2enable,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
    &mld_v2enable, 0, sysctl_mld_v2enable, "I",
    "Enable MLDv2 (debug purposes only)");

static int      mld_use_allow = 1;
SYSCTL_INT(_net_inet6_mld, OID_AUTO, use_allow, CTLFLAG_RW | CTLFLAG_LOCKED,
    &mld_use_allow, 0, "Use ALLOW/BLOCK for RFC 4604 SSM joins/leaves");

#ifdef MLD_DEBUG
int mld_debug = 0;
SYSCTL_INT(_net_inet6_mld, OID_AUTO,
    debug, CTLFLAG_RW | CTLFLAG_LOCKED, &mld_debug, 0, "");
#endif
/*
 * Packed Router Alert option structure declaration.
 */
struct mld_raopt {
        struct ip6_hbh          hbh;
        struct ip6_opt          pad;
        struct ip6_opt_router   ra;
} __packed;

/*
 * Router Alert hop-by-hop option header.
 */
static struct mld_raopt mld_ra = {
        .hbh = { .ip6h_nxt = 0, .ip6h_len = 0 },
        .pad = { .ip6o_type = IP6OPT_PADN, .ip6o_len = 0 },
        .ra = {
                .ip6or_type = (u_int8_t)IP6OPT_ROUTER_ALERT,
                .ip6or_len = (u_int8_t)(IP6OPT_RTALERT_LEN - 2),
                .ip6or_value =  {((IP6OPT_RTALERT_MLD >> 8) & 0xFF),
                                 (IP6OPT_RTALERT_MLD & 0xFF) }
        }
};
static struct ip6_pktopts mld_po;

/* Store MLDv2 record count in the module private scratch space */
#define vt_nrecs        pkt_mpriv.__mpriv_u.__mpriv32[0].__mpriv32_u.__val16[0]

static __inline void
mld_save_context(struct mbuf *m, struct ifnet *ifp)
{
        m->m_pkthdr.rcvif = ifp;
}

static __inline void
mld_scrub_context(struct mbuf *m)
{
        m->m_pkthdr.rcvif = NULL;
}

/*
 * Restore context from a queued output chain.
 * Return saved ifp.
 */
static __inline struct ifnet *
mld_restore_context(struct mbuf *m)
{
        return m->m_pkthdr.rcvif;
}

/*
 * Retrieve or set threshold between group-source queries in seconds.
 */
static int
sysctl_mld_gsr SYSCTL_HANDLER_ARGS
{
#pragma unused(arg1, arg2)
        int error;
        int i;

        MLD_LOCK();

        i = mld_gsrdelay.tv_sec;

        error = sysctl_handle_int(oidp, &i, 0, req);
        if (error || !req->newptr) {
                goto out_locked;
        }

        if (i < -1 || i >= 60) {
                error = EINVAL;
                goto out_locked;
        }

        mld_gsrdelay.tv_sec = i;

out_locked:
        MLD_UNLOCK();
        return error;
}
/*
 * Expose struct mld_ifinfo to userland, keyed by ifindex.
 * For use by ifmcstat(8).
 *
 */
static int
sysctl_mld_ifinfo SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp)
        int                     *name;
        int                      error;
        u_int                    namelen;
        struct ifnet            *ifp;
        struct mld_ifinfo       *mli;
        struct mld_ifinfo_u     mli_u;

        name = (int *)arg1;
        namelen = arg2;

        if (req->newptr != USER_ADDR_NULL) {
                return EPERM;
        }

        if (namelen != 1) {
                return EINVAL;
        }

        MLD_LOCK();

        if (name[0] <= 0 || name[0] > (u_int)if_index) {
                error = ENOENT;
                goto out_locked;
        }

        error = ENOENT;

        ifnet_head_lock_shared();
        ifp = ifindex2ifnet[name[0]];
        ifnet_head_done();
        if (ifp == NULL) {
                goto out_locked;
        }

        bzero(&mli_u, sizeof(mli_u));

        LIST_FOREACH(mli, &mli_head, mli_link) {
                MLI_LOCK(mli);
                if (ifp != mli->mli_ifp) {
                        MLI_UNLOCK(mli);
                        continue;
                }

                mli_u.mli_ifindex = mli->mli_ifp->if_index;
                mli_u.mli_version = mli->mli_version;
                mli_u.mli_v1_timer = mli->mli_v1_timer;
                mli_u.mli_v2_timer = mli->mli_v2_timer;
                mli_u.mli_flags = mli->mli_flags;
                mli_u.mli_rv = mli->mli_rv;
                mli_u.mli_qi = mli->mli_qi;
                mli_u.mli_qri = mli->mli_qri;
                mli_u.mli_uri = mli->mli_uri;
                MLI_UNLOCK(mli);

                error = SYSCTL_OUT(req, &mli_u, sizeof(mli_u));
                break;
        }

out_locked:
        MLD_UNLOCK();
        return error;
}

static int
sysctl_mld_v2enable SYSCTL_HANDLER_ARGS
{
#pragma unused(arg1, arg2)
        int error;
        int i;
        struct mld_ifinfo *mli;
        struct mld_tparams mtp = { .qpt = 0, .it = 0, .cst = 0, .sct = 0 };

        MLD_LOCK();

        i = mld_v2enable;

        error = sysctl_handle_int(oidp, &i, 0, req);
        if (error || !req->newptr) {
                goto out_locked;
        }

        if (i < 0 || i > 1) {
                error = EINVAL;
                goto out_locked;
        }

        mld_v2enable = i;
        /*
         * If we enabled v2, the state transition will take care of upgrading
         * the MLD version back to v2. Otherwise, we have to explicitly
         * downgrade. Note that this functionality is to be used for debugging.
         */
        if (mld_v2enable == 1) {
                goto out_locked;
        }

        LIST_FOREACH(mli, &mli_head, mli_link) {
                MLI_LOCK(mli);
                if (mld_set_version(mli, MLD_VERSION_1) > 0) {
                        mtp.qpt = 1;
                }
                MLI_UNLOCK(mli);
        }

out_locked:
        MLD_UNLOCK();

        mld_set_timeout(&mtp);

        return error;
}

/*
 * Dispatch an entire queue of pending packet chains.
 *
 * Must not be called with in6m_lock held.
 * XXX This routine unlocks MLD global lock and also mli locks.
 * Make sure that the calling routine takes reference on the mli
 * before calling this routine.
 * Also if we are traversing mli_head, remember to check for
 * mli list generation count and restart the loop if generation count
 * has changed.
 */
static void
mld_dispatch_queue_locked(struct mld_ifinfo *mli, struct ifqueue *ifq, int limit)
{
        struct mbuf *m;

        MLD_LOCK_ASSERT_HELD();

        if (mli != NULL) {
                MLI_LOCK_ASSERT_HELD(mli);
        }

        for (;;) {
                IF_DEQUEUE(ifq, m);
                if (m == NULL) {
                        break;
                }
                MLD_PRINTF(("%s: dispatch 0x%llx from 0x%llx\n", __func__,
                    (uint64_t)VM_KERNEL_ADDRPERM(ifq),
                    (uint64_t)VM_KERNEL_ADDRPERM(m)));

                if (mli != NULL) {
                        MLI_UNLOCK(mli);
                }
                MLD_UNLOCK();

                mld_dispatch_packet(m);

                MLD_LOCK();
                if (mli != NULL) {
                        MLI_LOCK(mli);
                }

                if (--limit == 0) {
                        break;
                }
        }

        if (mli != NULL) {
                MLI_LOCK_ASSERT_HELD(mli);
        }
}

/*
 * Filter outgoing MLD report state by group.
 *
 * Reports are ALWAYS suppressed for ALL-HOSTS (ff02::1)
 * and node-local addresses. However, kernel and socket consumers
 * always embed the KAME scope ID in the address provided, so strip it
 * when performing comparison.
 * Note: This is not the same as the *multicast* scope.
 *
 * Return zero if the given group is one for which MLD reports
 * should be suppressed, or non-zero if reports should be issued.
 */
static __inline__ int
mld_is_addr_reported(const struct in6_addr *addr)
{
        VERIFY(IN6_IS_ADDR_MULTICAST(addr));

        if (IPV6_ADDR_MC_SCOPE(addr) == IPV6_ADDR_SCOPE_NODELOCAL) {
                return 0;
        }

        if (IPV6_ADDR_MC_SCOPE(addr) == IPV6_ADDR_SCOPE_LINKLOCAL) {
                struct in6_addr tmp = *addr;
                in6_clearscope(&tmp);
                if (IN6_ARE_ADDR_EQUAL(&tmp, &in6addr_linklocal_allnodes)) {
                        return 0;
                }
        }

        return 1;
}

/*
 * Attach MLD when PF_INET6 is attached to an interface.
 */
struct mld_ifinfo *
mld_domifattach(struct ifnet *ifp, int how)
{
        struct mld_ifinfo *mli;

        MLD_PRINTF(("%s: called for ifp 0x%llx(%s)\n", __func__,
            (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));

        mli = mli_alloc(how);
        if (mli == NULL) {
                return NULL;
        }

        MLD_LOCK();

        MLI_LOCK(mli);
        mli_initvar(mli, ifp, 0);
        mli->mli_debug |= IFD_ATTACHED;
        MLI_ADDREF_LOCKED(mli); /* hold a reference for mli_head */
        MLI_ADDREF_LOCKED(mli); /* hold a reference for caller */
        MLI_UNLOCK(mli);
        ifnet_lock_shared(ifp);
        mld6_initsilent(ifp, mli);
        ifnet_lock_done(ifp);

        LIST_INSERT_HEAD(&mli_head, mli, mli_link);
        mld_mli_list_genid++;

        MLD_UNLOCK();

        MLD_PRINTF(("%s: allocate mld_ifinfo for ifp 0x%llx(%s)\n",
            __func__, (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));

        return mli;
}

/*
 * Attach MLD when PF_INET6 is reattached to an interface.  Caller is
 * expected to have an outstanding reference to the mli.
 */
void
mld_domifreattach(struct mld_ifinfo *mli)
{
        struct ifnet *ifp;

        MLD_LOCK();

        MLI_LOCK(mli);
        VERIFY(!(mli->mli_debug & IFD_ATTACHED));
        ifp = mli->mli_ifp;
        VERIFY(ifp != NULL);
        mli_initvar(mli, ifp, 1);
        mli->mli_debug |= IFD_ATTACHED;
        MLI_ADDREF_LOCKED(mli); /* hold a reference for mli_head */
        MLI_UNLOCK(mli);
        ifnet_lock_shared(ifp);
        mld6_initsilent(ifp, mli);
        ifnet_lock_done(ifp);

        LIST_INSERT_HEAD(&mli_head, mli, mli_link);
        mld_mli_list_genid++;

        MLD_UNLOCK();

        MLD_PRINTF(("%s: reattached mld_ifinfo for ifp 0x%llx(%s)\n",
            __func__, (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
}

/*
 * Hook for domifdetach.
 */
void
mld_domifdetach(struct ifnet *ifp)
{
        SLIST_HEAD(, in6_multi) in6m_dthead;

        SLIST_INIT(&in6m_dthead);

        MLD_PRINTF(("%s: called for ifp 0x%llx(%s)\n", __func__,
            (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));

        MLD_LOCK();
        mli_delete(ifp, (struct mld_in6m_relhead *)&in6m_dthead);
        MLD_UNLOCK();

        /* Now that we're dropped all locks, release detached records */
        MLD_REMOVE_DETACHED_IN6M(&in6m_dthead);
}

/*
 * Called at interface detach time.  Note that we only flush all deferred
 * responses and record releases; all remaining inm records and their source
 * entries related to this interface are left intact, in order to handle
 * the reattach case.
 */
static void
mli_delete(const struct ifnet *ifp, struct mld_in6m_relhead *in6m_dthead)
{
        struct mld_ifinfo *mli, *tmli;

        MLD_LOCK_ASSERT_HELD();

        LIST_FOREACH_SAFE(mli, &mli_head, mli_link, tmli) {
                MLI_LOCK(mli);
                if (mli->mli_ifp == ifp) {
                        /*
                         * Free deferred General Query responses.
                         */
                        IF_DRAIN(&mli->mli_gq);
                        IF_DRAIN(&mli->mli_v1q);
                        mld_flush_relq(mli, in6m_dthead);
                        VERIFY(SLIST_EMPTY(&mli->mli_relinmhead));
                        mli->mli_debug &= ~IFD_ATTACHED;
                        MLI_UNLOCK(mli);

                        LIST_REMOVE(mli, mli_link);
                        MLI_REMREF(mli); /* release mli_head reference */
                        mld_mli_list_genid++;
                        return;
                }
                MLI_UNLOCK(mli);
        }
        panic("%s: mld_ifinfo not found for ifp %p(%s)\n", __func__,
            ifp, ifp->if_xname);
}

__private_extern__ void
mld6_initsilent(struct ifnet *ifp, struct mld_ifinfo *mli)
{
        ifnet_lock_assert(ifp, IFNET_LCK_ASSERT_OWNED);

        MLI_LOCK_ASSERT_NOTHELD(mli);
        MLI_LOCK(mli);
        if (!(ifp->if_flags & IFF_MULTICAST) &&
            (ifp->if_eflags & (IFEF_IPV6_ND6ALT | IFEF_LOCALNET_PRIVATE))) {
                mli->mli_flags |= MLIF_SILENT;
        } else {
                mli->mli_flags &= ~MLIF_SILENT;
        }
        MLI_UNLOCK(mli);
}

static void
mli_initvar(struct mld_ifinfo *mli, struct ifnet *ifp, int reattach)
{
        MLI_LOCK_ASSERT_HELD(mli);

        mli->mli_ifp = ifp;
        if (mld_v2enable) {
                mli->mli_version = MLD_VERSION_2;
        } else {
                mli->mli_version = MLD_VERSION_1;
        }
        mli->mli_flags = 0;
        mli->mli_rv = MLD_RV_INIT;
        mli->mli_qi = MLD_QI_INIT;
        mli->mli_qri = MLD_QRI_INIT;
        mli->mli_uri = MLD_URI_INIT;

        if (mld_use_allow) {
                mli->mli_flags |= MLIF_USEALLOW;
        }
        if (!reattach) {
                SLIST_INIT(&mli->mli_relinmhead);
        }

        /*
         * Responses to general queries are subject to bounds.
         */
        mli->mli_gq.ifq_maxlen = MLD_MAX_RESPONSE_PACKETS;
        mli->mli_v1q.ifq_maxlen = MLD_MAX_RESPONSE_PACKETS;
}

static struct mld_ifinfo *
mli_alloc(int how)
{
        struct mld_ifinfo *mli;

        mli = (how == M_WAITOK) ? zalloc(mli_zone) : zalloc_noblock(mli_zone);
        if (mli != NULL) {
                bzero(mli, mli_size);
                lck_mtx_init(&mli->mli_lock, mld_mtx_grp, mld_mtx_attr);
                mli->mli_debug |= IFD_ALLOC;
        }
        return mli;
}

static void
mli_free(struct mld_ifinfo *mli)
{
        MLI_LOCK(mli);
        if (mli->mli_debug & IFD_ATTACHED) {
                panic("%s: attached mli=%p is being freed", __func__, mli);
                /* NOTREACHED */
        } else if (mli->mli_ifp != NULL) {
                panic("%s: ifp not NULL for mli=%p", __func__, mli);
                /* NOTREACHED */
        } else if (!(mli->mli_debug & IFD_ALLOC)) {
                panic("%s: mli %p cannot be freed", __func__, mli);
                /* NOTREACHED */
        } else if (mli->mli_refcnt != 0) {
                panic("%s: non-zero refcnt mli=%p", __func__, mli);
                /* NOTREACHED */
        }
        mli->mli_debug &= ~IFD_ALLOC;
        MLI_UNLOCK(mli);

        lck_mtx_destroy(&mli->mli_lock, mld_mtx_grp);
        zfree(mli_zone, mli);
}

void
mli_addref(struct mld_ifinfo *mli, int locked)
{
        if (!locked) {
                MLI_LOCK_SPIN(mli);
        } else {
                MLI_LOCK_ASSERT_HELD(mli);
        }

        if (++mli->mli_refcnt == 0) {
                panic("%s: mli=%p wraparound refcnt", __func__, mli);
                /* NOTREACHED */
        }
        if (!locked) {
                MLI_UNLOCK(mli);
        }
}

void
mli_remref(struct mld_ifinfo *mli)
{
        SLIST_HEAD(, in6_multi) in6m_dthead;
        struct ifnet *ifp;

        MLI_LOCK_SPIN(mli);

        if (mli->mli_refcnt == 0) {
                panic("%s: mli=%p negative refcnt", __func__, mli);
                /* NOTREACHED */
        }

        --mli->mli_refcnt;
        if (mli->mli_refcnt > 0) {
                MLI_UNLOCK(mli);
                return;
        }

        ifp = mli->mli_ifp;
        mli->mli_ifp = NULL;
        IF_DRAIN(&mli->mli_gq);
        IF_DRAIN(&mli->mli_v1q);
        SLIST_INIT(&in6m_dthead);
        mld_flush_relq(mli, (struct mld_in6m_relhead *)&in6m_dthead);
        VERIFY(SLIST_EMPTY(&mli->mli_relinmhead));
        MLI_UNLOCK(mli);

        /* Now that we're dropped all locks, release detached records */
        MLD_REMOVE_DETACHED_IN6M(&in6m_dthead);

        MLD_PRINTF(("%s: freeing mld_ifinfo for ifp 0x%llx(%s)\n",
            __func__, (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));

        mli_free(mli);
}

/*
 * Process a received MLDv1 general or address-specific query.
 * Assumes that the query header has been pulled up to sizeof(mld_hdr).
 *
 * NOTE: Can't be fully const correct as we temporarily embed scope ID in
 * mld_addr. This is OK as we own the mbuf chain.
 */
static int
mld_v1_input_query(struct ifnet *ifp, const struct ip6_hdr *ip6,
    /*const*/ struct mld_hdr *mld)
{
        struct mld_ifinfo       *mli;
        struct in6_multi        *inm;
        int                      err = 0, is_general_query;
        uint16_t                 timer;
        struct mld_tparams       mtp = { .qpt = 0, .it = 0, .cst = 0, .sct = 0 };

        MLD_LOCK_ASSERT_NOTHELD();

        is_general_query = 0;

        if (!mld_v1enable) {
                MLD_PRINTF(("%s: ignore v1 query %s on ifp 0x%llx(%s)\n",
                    __func__, ip6_sprintf(&mld->mld_addr),
                    (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                goto done;
        }

        /*
         * RFC3810 Section 6.2: MLD queries must originate from
         * a router's link-local address.
         */
        if (!IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src)) {
                MLD_PRINTF(("%s: ignore v1 query src %s on ifp 0x%llx(%s)\n",
                    __func__, ip6_sprintf(&ip6->ip6_src),
                    (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                goto done;
        }

        /*
         * Do address field validation upfront before we accept
         * the query.
         */
        if (IN6_IS_ADDR_UNSPECIFIED(&mld->mld_addr)) {
                /*
                 * MLDv1 General Query.
                 * If this was not sent to the all-nodes group, ignore it.
                 */
                struct in6_addr          dst;

                dst = ip6->ip6_dst;
                in6_clearscope(&dst);
                if (!IN6_ARE_ADDR_EQUAL(&dst, &in6addr_linklocal_allnodes)) {
                        err = EINVAL;
                        goto done;
                }
                is_general_query = 1;
        } else {
                /*
                 * Embed scope ID of receiving interface in MLD query for
                 * lookup whilst we don't hold other locks.
                 */
                (void)in6_setscope(&mld->mld_addr, ifp, NULL);
        }

        /*
         * Switch to MLDv1 host compatibility mode.
         */
        mli = MLD_IFINFO(ifp);
        VERIFY(mli != NULL);

        MLI_LOCK(mli);
        mtp.qpt = mld_set_version(mli, MLD_VERSION_1);
        MLI_UNLOCK(mli);

        timer = ntohs(mld->mld_maxdelay) / MLD_TIMER_SCALE;
        if (timer == 0) {
                timer = 1;
        }

        if (is_general_query) {
                struct in6_multistep step;

                MLD_PRINTF(("%s: process v1 general query on ifp 0x%llx(%s)\n",
                    __func__, (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                /*
                 * For each reporting group joined on this
                 * interface, kick the report timer.
                 */
                in6_multihead_lock_shared();
                IN6_FIRST_MULTI(step, inm);
                while (inm != NULL) {
                        IN6M_LOCK(inm);
                        if (inm->in6m_ifp == ifp) {
                                mtp.cst += mld_v1_update_group(inm, timer);
                        }
                        IN6M_UNLOCK(inm);
                        IN6_NEXT_MULTI(step, inm);
                }
                in6_multihead_lock_done();
        } else {
                /*
                 * MLDv1 Group-Specific Query.
                 * If this is a group-specific MLDv1 query, we need only
                 * look up the single group to process it.
                 */
                in6_multihead_lock_shared();
                IN6_LOOKUP_MULTI(&mld->mld_addr, ifp, inm);
                in6_multihead_lock_done();

                if (inm != NULL) {
                        IN6M_LOCK(inm);
                        MLD_PRINTF(("%s: process v1 query %s on "
                            "ifp 0x%llx(%s)\n", __func__,
                            ip6_sprintf(&mld->mld_addr),
                            (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                        mtp.cst = mld_v1_update_group(inm, timer);
                        IN6M_UNLOCK(inm);
                        IN6M_REMREF(inm); /* from IN6_LOOKUP_MULTI */
                }
                /* XXX Clear embedded scope ID as userland won't expect it. */
                in6_clearscope(&mld->mld_addr);
        }
done:
        mld_set_timeout(&mtp);

        return err;
}

/*
 * Update the report timer on a group in response to an MLDv1 query.
 *
 * If we are becoming the reporting member for this group, start the timer.
 * If we already are the reporting member for this group, and timer is
 * below the threshold, reset it.
 *
 * We may be updating the group for the first time since we switched
 * to MLDv2. If we are, then we must clear any recorded source lists,
 * and transition to REPORTING state; the group timer is overloaded
 * for group and group-source query responses.
 *
 * Unlike MLDv2, the delay per group should be jittered
 * to avoid bursts of MLDv1 reports.
 */
static uint32_t
mld_v1_update_group(struct in6_multi *inm, const int timer)
{
        IN6M_LOCK_ASSERT_HELD(inm);

        MLD_PRINTF(("%s: %s/%s timer=%d\n", __func__,
            ip6_sprintf(&inm->in6m_addr),
            if_name(inm->in6m_ifp), timer));

        switch (inm->in6m_state) {
        case MLD_NOT_MEMBER:
        case MLD_SILENT_MEMBER:
                break;
        case MLD_REPORTING_MEMBER:
                if (inm->in6m_timer != 0 &&
                    inm->in6m_timer <= timer) {
                        MLD_PRINTF(("%s: REPORTING and timer running, "
                            "skipping.\n", __func__));
                        break;
                }
        /* FALLTHROUGH */
        case MLD_SG_QUERY_PENDING_MEMBER:
        case MLD_G_QUERY_PENDING_MEMBER:
        case MLD_IDLE_MEMBER:
        case MLD_LAZY_MEMBER:
        case MLD_AWAKENING_MEMBER:
                MLD_PRINTF(("%s: ->REPORTING\n", __func__));
                inm->in6m_state = MLD_REPORTING_MEMBER;
                inm->in6m_timer = MLD_RANDOM_DELAY(timer);
                break;
        case MLD_SLEEPING_MEMBER:
                MLD_PRINTF(("%s: ->AWAKENING\n", __func__));
                inm->in6m_state = MLD_AWAKENING_MEMBER;
                break;
        case MLD_LEAVING_MEMBER:
                break;
        }

        return inm->in6m_timer;
}

/*
 * Process a received MLDv2 general, group-specific or
 * group-and-source-specific query.
 *
 * Assumes that the query header has been pulled up to sizeof(mldv2_query).
 *
 * Return 0 if successful, otherwise an appropriate error code is returned.
 */
static int
mld_v2_input_query(struct ifnet *ifp, const struct ip6_hdr *ip6,
    struct mbuf *m, const int off, const int icmp6len)
{
        struct mld_ifinfo       *mli;
        struct mldv2_query      *mld;
        struct in6_multi        *inm;
        uint32_t                 maxdelay, nsrc, qqi;
        int                      err = 0, is_general_query;
        uint16_t                 timer;
        uint8_t                  qrv;
        struct mld_tparams       mtp = { .qpt = 0, .it = 0, .cst = 0, .sct = 0 };

        MLD_LOCK_ASSERT_NOTHELD();

        is_general_query = 0;

        if (!mld_v2enable) {
                MLD_PRINTF(("%s: ignore v2 query %s on ifp 0x%llx(%s)\n",
                    __func__, ip6_sprintf(&ip6->ip6_src),
                    (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                goto done;
        }

        /*
         * RFC3810 Section 6.2: MLD queries must originate from
         * a router's link-local address.
         */
        if (!IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src)) {
                MLD_PRINTF(("%s: ignore v1 query src %s on ifp 0x%llx(%s)\n",
                    __func__, ip6_sprintf(&ip6->ip6_src),
                    (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                goto done;
        }

        MLD_PRINTF(("%s: input v2 query on ifp 0x%llx(%s)\n", __func__,
            (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));

        mld = (struct mldv2_query *)(mtod(m, uint8_t *) + off);

        maxdelay = ntohs(mld->mld_maxdelay);    /* in 1/10ths of a second */
        if (maxdelay >= 32768) {
                maxdelay = (MLD_MRC_MANT(maxdelay) | 0x1000) <<
                    (MLD_MRC_EXP(maxdelay) + 3);
        }
        timer = maxdelay / MLD_TIMER_SCALE;
        if (timer == 0) {
                timer = 1;
        }

        qrv = MLD_QRV(mld->mld_misc);
        if (qrv < 2) {
                MLD_PRINTF(("%s: clamping qrv %d to %d\n", __func__,
                    qrv, MLD_RV_INIT));
                qrv = MLD_RV_INIT;
        }

        qqi = mld->mld_qqi;
        if (qqi >= 128) {
                qqi = MLD_QQIC_MANT(mld->mld_qqi) <<
                    (MLD_QQIC_EXP(mld->mld_qqi) + 3);
        }

        nsrc = ntohs(mld->mld_numsrc);
        if (nsrc > MLD_MAX_GS_SOURCES) {
                err = EMSGSIZE;
                goto done;
        }
        if (icmp6len < sizeof(struct mldv2_query) +
            (nsrc * sizeof(struct in6_addr))) {
                err = EMSGSIZE;
                goto done;
        }

        /*
         * Do further input validation upfront to avoid resetting timers
         * should we need to discard this query.
         */
        if (IN6_IS_ADDR_UNSPECIFIED(&mld->mld_addr)) {
                /*
                 * A general query with a source list has undefined
                 * behaviour; discard it.
                 */
                if (nsrc > 0) {
                        err = EINVAL;
                        goto done;
                }
                is_general_query = 1;
        } else {
                /*
                 * Embed scope ID of receiving interface in MLD query for
                 * lookup whilst we don't hold other locks (due to KAME
                 * locking lameness). We own this mbuf chain just now.
                 */
                (void)in6_setscope(&mld->mld_addr, ifp, NULL);
        }

        mli = MLD_IFINFO(ifp);
        VERIFY(mli != NULL);

        MLI_LOCK(mli);
        /*
         * Discard the v2 query if we're in Compatibility Mode.
         * The RFC is pretty clear that hosts need to stay in MLDv1 mode
         * until the Old Version Querier Present timer expires.
         */
        if (mli->mli_version != MLD_VERSION_2) {
                MLI_UNLOCK(mli);
                goto done;
        }

        mtp.qpt = mld_set_version(mli, MLD_VERSION_2);
        mli->mli_rv = qrv;
        mli->mli_qi = qqi;
        mli->mli_qri = MAX(timer, MLD_QRI_MIN);

        MLD_PRINTF(("%s: qrv %d qi %d qri %d\n", __func__, mli->mli_rv,
            mli->mli_qi, mli->mli_qri));

        if (is_general_query) {
                /*
                 * MLDv2 General Query.
                 *
                 * Schedule a current-state report on this ifp for
                 * all groups, possibly containing source lists.
                 *
                 * If there is a pending General Query response
                 * scheduled earlier than the selected delay, do
                 * not schedule any other reports.
                 * Otherwise, reset the interface timer.
                 */
                MLD_PRINTF(("%s: process v2 general query on ifp 0x%llx(%s)\n",
                    __func__, (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                if (mli->mli_v2_timer == 0 || mli->mli_v2_timer >= timer) {
                        mtp.it = mli->mli_v2_timer = MLD_RANDOM_DELAY(timer);
                }
                MLI_UNLOCK(mli);
        } else {
                MLI_UNLOCK(mli);
                /*
                 * MLDv2 Group-specific or Group-and-source-specific Query.
                 *
                 * Group-source-specific queries are throttled on
                 * a per-group basis to defeat denial-of-service attempts.
                 * Queries for groups we are not a member of on this
                 * link are simply ignored.
                 */
                in6_multihead_lock_shared();
                IN6_LOOKUP_MULTI(&mld->mld_addr, ifp, inm);
                in6_multihead_lock_done();
                if (inm == NULL) {
                        goto done;
                }

                IN6M_LOCK(inm);
                if (nsrc > 0) {
                        if (!ratecheck(&inm->in6m_lastgsrtv,
                            &mld_gsrdelay)) {
                                MLD_PRINTF(("%s: GS query throttled.\n",
                                    __func__));
                                IN6M_UNLOCK(inm);
                                IN6M_REMREF(inm); /* from IN6_LOOKUP_MULTI */
                                goto done;
                        }
                }
                MLD_PRINTF(("%s: process v2 group query on ifp 0x%llx(%s)\n",
                    __func__, (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                /*
                 * If there is a pending General Query response
                 * scheduled sooner than the selected delay, no
                 * further report need be scheduled.
                 * Otherwise, prepare to respond to the
                 * group-specific or group-and-source query.
                 */
                MLI_LOCK(mli);
                mtp.it = mli->mli_v2_timer;
                MLI_UNLOCK(mli);
                if (mtp.it == 0 || mtp.it >= timer) {
                        (void) mld_v2_process_group_query(inm, timer, m, off);
                        mtp.cst = inm->in6m_timer;
                }
                IN6M_UNLOCK(inm);
                IN6M_REMREF(inm); /* from IN6_LOOKUP_MULTI */
                /* XXX Clear embedded scope ID as userland won't expect it. */
                in6_clearscope(&mld->mld_addr);
        }
done:
        if (mtp.it > 0) {
                MLD_PRINTF(("%s: v2 general query response scheduled in "
                    "T+%d seconds on ifp 0x%llx(%s)\n", __func__, mtp.it,
                    (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
        }
        mld_set_timeout(&mtp);

        return err;
}

/*
 * Process a recieved MLDv2 group-specific or group-and-source-specific
 * query.
 * Return <0 if any error occured. Currently this is ignored.
 */
static int
mld_v2_process_group_query(struct in6_multi *inm, int timer, struct mbuf *m0,
    const int off)
{
        struct mldv2_query      *mld;
        int                      retval;
        uint16_t                 nsrc;

        IN6M_LOCK_ASSERT_HELD(inm);

        retval = 0;
        mld = (struct mldv2_query *)(mtod(m0, uint8_t *) + off);

        switch (inm->in6m_state) {
        case MLD_NOT_MEMBER:
        case MLD_SILENT_MEMBER:
        case MLD_SLEEPING_MEMBER:
        case MLD_LAZY_MEMBER:
        case MLD_AWAKENING_MEMBER:
        case MLD_IDLE_MEMBER:
        case MLD_LEAVING_MEMBER:
                return retval;
        case MLD_REPORTING_MEMBER:
        case MLD_G_QUERY_PENDING_MEMBER:
        case MLD_SG_QUERY_PENDING_MEMBER:
                break;
        }

        nsrc = ntohs(mld->mld_numsrc);

        /*
         * Deal with group-specific queries upfront.
         * If any group query is already pending, purge any recorded
         * source-list state if it exists, and schedule a query response
         * for this group-specific query.
         */
        if (nsrc == 0) {
                if (inm->in6m_state == MLD_G_QUERY_PENDING_MEMBER ||
                    inm->in6m_state == MLD_SG_QUERY_PENDING_MEMBER) {
                        in6m_clear_recorded(inm);
                        timer = min(inm->in6m_timer, timer);
                }
                inm->in6m_state = MLD_G_QUERY_PENDING_MEMBER;
                inm->in6m_timer = MLD_RANDOM_DELAY(timer);
                return retval;
        }

        /*
         * Deal with the case where a group-and-source-specific query has
         * been received but a group-specific query is already pending.
         */
        if (inm->in6m_state == MLD_G_QUERY_PENDING_MEMBER) {
                timer = min(inm->in6m_timer, timer);
                inm->in6m_timer = MLD_RANDOM_DELAY(timer);
                return retval;
        }

        /*
         * Finally, deal with the case where a group-and-source-specific
         * query has been received, where a response to a previous g-s-r
         * query exists, or none exists.
         * In this case, we need to parse the source-list which the Querier
         * has provided us with and check if we have any source list filter
         * entries at T1 for these sources. If we do not, there is no need
         * schedule a report and the query may be dropped.
         * If we do, we must record them and schedule a current-state
         * report for those sources.
         */
        if (inm->in6m_nsrc > 0) {
                struct mbuf             *m;
                uint8_t                 *sp;
                int                      i, nrecorded;
                int                      soff;

                m = m0;
                soff = off + sizeof(struct mldv2_query);
                nrecorded = 0;
                for (i = 0; i < nsrc; i++) {
                        sp = mtod(m, uint8_t *) + soff;
                        retval = in6m_record_source(inm,
                            (const struct in6_addr *)(void *)sp);
                        if (retval < 0) {
                                break;
                        }
                        nrecorded += retval;
                        soff += sizeof(struct in6_addr);
                        if (soff >= m->m_len) {
                                soff = soff - m->m_len;
                                m = m->m_next;
                                if (m == NULL) {
                                        break;
                                }
                        }
                }
                if (nrecorded > 0) {
                        MLD_PRINTF(("%s: schedule response to SG query\n",
                            __func__));
                        inm->in6m_state = MLD_SG_QUERY_PENDING_MEMBER;
                        inm->in6m_timer = MLD_RANDOM_DELAY(timer);
                }
        }

        return retval;
}

/*
 * Process a received MLDv1 host membership report.
 * Assumes mld points to mld_hdr in pulled up mbuf chain.
 *
 * NOTE: Can't be fully const correct as we temporarily embed scope ID in
 * mld_addr. This is OK as we own the mbuf chain.
 */
static int
mld_v1_input_report(struct ifnet *ifp, struct mbuf *m,
    const struct ip6_hdr *ip6, /*const*/ struct mld_hdr *mld)
{
        struct in6_addr          src, dst;
        struct in6_ifaddr       *ia;
        struct in6_multi        *inm;

        if (!mld_v1enable) {
                MLD_PRINTF(("%s: ignore v1 report %s on ifp 0x%llx(%s)\n",
                    __func__, ip6_sprintf(&mld->mld_addr),
                    (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                return 0;
        }

        if ((ifp->if_flags & IFF_LOOPBACK) ||
            (m->m_pkthdr.pkt_flags & PKTF_LOOP)) {
                return 0;
        }

        /*
         * MLDv1 reports must originate from a host's link-local address,
         * or the unspecified address (when booting).
         */
        src = ip6->ip6_src;
        in6_clearscope(&src);
        if (!IN6_IS_SCOPE_LINKLOCAL(&src) && !IN6_IS_ADDR_UNSPECIFIED(&src)) {
                MLD_PRINTF(("%s: ignore v1 query src %s on ifp 0x%llx(%s)\n",
                    __func__, ip6_sprintf(&ip6->ip6_src),
                    (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                return EINVAL;
        }

        /*
         * RFC2710 Section 4: MLDv1 reports must pertain to a multicast
         * group, and must be directed to the group itself.
         */
        dst = ip6->ip6_dst;
        in6_clearscope(&dst);
        if (!IN6_IS_ADDR_MULTICAST(&mld->mld_addr) ||
            !IN6_ARE_ADDR_EQUAL(&mld->mld_addr, &dst)) {
                MLD_PRINTF(("%s: ignore v1 query dst %s on ifp 0x%llx(%s)\n",
                    __func__, ip6_sprintf(&ip6->ip6_dst),
                    (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                return EINVAL;
        }

        /*
         * Make sure we don't hear our own membership report, as fast
         * leave requires knowing that we are the only member of a
         * group. Assume we used the link-local address if available,
         * otherwise look for ::.
         *
         * XXX Note that scope ID comparison is needed for the address
         * returned by in6ifa_ifpforlinklocal(), but SHOULD NOT be
         * performed for the on-wire address.
         */
        ia = in6ifa_ifpforlinklocal(ifp, IN6_IFF_NOTREADY | IN6_IFF_ANYCAST);
        if (ia != NULL) {
                IFA_LOCK(&ia->ia_ifa);
                if ((IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, IA6_IN6(ia)))) {
                        IFA_UNLOCK(&ia->ia_ifa);
                        IFA_REMREF(&ia->ia_ifa);
                        return 0;
                }
                IFA_UNLOCK(&ia->ia_ifa);
                IFA_REMREF(&ia->ia_ifa);
        } else if (IN6_IS_ADDR_UNSPECIFIED(&src)) {
                return 0;
        }

        MLD_PRINTF(("%s: process v1 report %s on ifp 0x%llx(%s)\n",
            __func__, ip6_sprintf(&mld->mld_addr),
            (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));

        /*
         * Embed scope ID of receiving interface in MLD query for lookup
         * whilst we don't hold other locks (due to KAME locking lameness).
         */
        if (!IN6_IS_ADDR_UNSPECIFIED(&mld->mld_addr)) {
                (void)in6_setscope(&mld->mld_addr, ifp, NULL);
        }

        /*
         * MLDv1 report suppression.
         * If we are a member of this group, and our membership should be
         * reported, and our group timer is pending or about to be reset,
         * stop our group timer by transitioning to the 'lazy' state.
         */
        in6_multihead_lock_shared();
        IN6_LOOKUP_MULTI(&mld->mld_addr, ifp, inm);
        in6_multihead_lock_done();

        if (inm != NULL) {
                struct mld_ifinfo *mli;

                IN6M_LOCK(inm);
                mli = inm->in6m_mli;
                VERIFY(mli != NULL);

                MLI_LOCK(mli);
                /*
                 * If we are in MLDv2 host mode, do not allow the
                 * other host's MLDv1 report to suppress our reports.
                 */
                if (mli->mli_version == MLD_VERSION_2) {
                        MLI_UNLOCK(mli);
                        IN6M_UNLOCK(inm);
                        IN6M_REMREF(inm); /* from IN6_LOOKUP_MULTI */
                        goto out;
                }
                MLI_UNLOCK(mli);

                inm->in6m_timer = 0;

                switch (inm->in6m_state) {
                case MLD_NOT_MEMBER:
                case MLD_SILENT_MEMBER:
                case MLD_SLEEPING_MEMBER:
                        break;
                case MLD_REPORTING_MEMBER:
                case MLD_IDLE_MEMBER:
                case MLD_AWAKENING_MEMBER:
                        MLD_PRINTF(("%s: report suppressed for %s on "
                            "ifp 0x%llx(%s)\n", __func__,
                            ip6_sprintf(&mld->mld_addr),
                            (uint64_t)VM_KERNEL_ADDRPERM(ifp), if_name(ifp)));
                case MLD_LAZY_MEMBER:
                        inm->in6m_state = MLD_LAZY_MEMBER;
                        break;
                case MLD_G_QUERY_PENDING_MEMBER:
                case MLD_SG_QUERY_PENDING_MEMBER:
                case MLD_LEAVING_MEMBER:
                        break;
                }
                IN6M_UNLOCK(inm);
                IN6M_REMREF(inm); /* from IN6_LOOKUP_MULTI */
        }

out:
        /* XXX Clear embedded scope ID as userland won't expect it. */
        in6_clearscope(&mld->mld_addr);

        return 0;
}

/*
 * MLD input path.
 *
 * Assume query messages which fit in a single ICMPv6 message header
 * have been pulled up.
 * Assume that userland will want to see the message, even if it
 * otherwise fails kernel input validation; do not free it.
 * Pullup may however free the mbuf chain m if it fails.
 *
 * Return IPPROTO_DONE if we freed m. Otherwise, return 0.
 */
int
mld_input(struct mbuf *m, int off, int icmp6len)
{
        struct ifnet    *ifp;
        struct ip6_hdr  *ip6;
        struct mld_hdr  *mld;
        int              mldlen;

        MLD_PRINTF(("%s: called w/mbuf (0x%llx,%d)\n", __func__,
            (uint64_t)VM_KERNEL_ADDRPERM(m), off));

        ifp = m->m_pkthdr.rcvif;

        ip6 = mtod(m, struct ip6_hdr *);

        /* Pullup to appropriate size. */
        mld = (struct mld_hdr *)(mtod(m, uint8_t *) + off);
        if (mld->mld_type == MLD_LISTENER_QUERY &&
            icmp6len >= sizeof(struct mldv2_query)) {
                mldlen = sizeof(struct mldv2_query);
        } else {
                mldlen = sizeof(struct mld_hdr);
        }
        // check if mldv2_query/mld_hdr fits in the first mbuf
        IP6_EXTHDR_CHECK(m, off, mldlen, return IPPROTO_DONE);
        IP6_EXTHDR_GET(mld, struct mld_hdr *, m, off, mldlen);
        if (mld == NULL) {
                icmp6stat.icp6s_badlen++;
                return IPPROTO_DONE;
        }

        /*
         * Userland needs to see all of this traffic for implementing
         * the endpoint discovery portion of multicast routing.
         */
        switch (mld->mld_type) {
        case MLD_LISTENER_QUERY:
                icmp6_ifstat_inc(ifp, ifs6_in_mldquery);
                if (icmp6len == sizeof(struct mld_hdr)) {
                        if (mld_v1_input_query(ifp, ip6, mld) != 0) {
                                return 0;
                        }
                } else if (icmp6len >= sizeof(struct mldv2_query)) {
                        if (mld_v2_input_query(ifp, ip6, m, off,
                            icmp6len) != 0) {
                                return 0;
                        }
                }
                break;
        case MLD_LISTENER_REPORT:
                icmp6_ifstat_inc(ifp, ifs6_in_mldreport);
                if (mld_v1_input_report(ifp, m, ip6, mld) != 0) {
                        return 0;
                }
                break;
        case MLDV2_LISTENER_REPORT:
                icmp6_ifstat_inc(ifp, ifs6_in_mldreport);
                break;
        case MLD_LISTENER_DONE:
                icmp6_ifstat_inc(ifp, ifs6_in_mlddone);
                break;
        default:
                break;
        }

        return 0;
}

/*
 * Schedule MLD timer based on various parameters; caller must ensure that
 * lock ordering is maintained as this routine acquires MLD global lock.
 */
void
mld_set_timeout(struct mld_tparams *mtp)
{
        MLD_LOCK_ASSERT_NOTHELD();
        VERIFY(mtp != NULL);

        if (mtp->qpt != 0 || mtp->it != 0 || mtp->cst != 0 || mtp->sct != 0) {
                MLD_LOCK();
                if (mtp->qpt != 0) {
                        querier_present_timers_running6 = 1;
                }
                if (mtp->it != 0) {
                        interface_timers_running6 = 1;
                }
                if (mtp->cst != 0) {
                        current_state_timers_running6 = 1;
                }
                if (mtp->sct != 0) {
                        state_change_timers_running6 = 1;
                }
                mld_sched_timeout();
                MLD_UNLOCK();
        }
}

/*
 * MLD6 timer handler (per 1 second).
 */
static void
mld_timeout(void *arg)
{
#pragma unused(arg)
        struct ifqueue           scq;   /* State-change packets */
        struct ifqueue           qrq;   /* Query response packets */
        struct ifnet            *ifp;
        struct mld_ifinfo       *mli;
        struct in6_multi        *inm;
        int                      uri_sec = 0;
        unsigned int genid = mld_mli_list_genid;

        SLIST_HEAD(, in6_multi) in6m_dthead;

        SLIST_INIT(&in6m_dthead);

        /*
         * Update coarse-grained networking timestamp (in sec.); the idea
         * is to piggy-back on the timeout callout to update the counter
         * returnable via net_uptime().
         */
        net_update_uptime();

        MLD_LOCK();

        MLD_PRINTF(("%s: qpt %d, it %d, cst %d, sct %d\n", __func__,
            querier_present_timers_running6, interface_timers_running6,
            current_state_timers_running6, state_change_timers_running6));

        /*
         * MLDv1 querier present timer processing.
         */
        if (querier_present_timers_running6) {
                querier_present_timers_running6 = 0;
                LIST_FOREACH(mli, &mli_head, mli_link) {
                        MLI_LOCK(mli);
                        mld_v1_process_querier_timers(mli);
                        if (mli->mli_v1_timer > 0) {
                                querier_present_timers_running6 = 1;
                        }
                        MLI_UNLOCK(mli);
                }
        }

        /*
         * MLDv2 General Query response timer processing.
         */
        if (interface_timers_running6) {
                MLD_PRINTF(("%s: interface timers running\n", __func__));
                interface_timers_running6 = 0;
                mli = LIST_FIRST(&mli_head);

                while (mli != NULL) {
                        if (mli->mli_flags & MLIF_PROCESSED) {
                                mli = LIST_NEXT(mli, mli_link);
                                continue;
                        }

                        MLI_LOCK(mli);
                        if (mli->mli_version != MLD_VERSION_2) {
                                MLI_UNLOCK(mli);
                                mli = LIST_NEXT(mli, mli_link);
                                continue;
                        }
                        /*
                         * XXX The logic below ends up calling
                         * mld_dispatch_packet which can unlock mli
                         * and the global MLD lock.
                         * Therefore grab a reference on MLI and also
                         * check for generation count to see if we should
                         * iterate the list again.
                         */
                        MLI_ADDREF_LOCKED(mli);

                        if (mli->mli_v2_timer == 0) {
                                /* Do nothing. */
                        } else if (--mli->mli_v2_timer == 0) {
                                if (mld_v2_dispatch_general_query(mli) > 0) {
                                        interface_timers_running6 = 1;
                                }
                        } else {
                                interface_timers_running6 = 1;
                        }
                        mli->mli_flags |= MLIF_PROCESSED;
                        MLI_UNLOCK(mli);
                        MLI_REMREF(mli);

                        if (genid != mld_mli_list_genid) {
                                MLD_PRINTF(("%s: MLD information list changed "
                                    "in the middle of iteration! Restart iteration.\n",
                                    __func__));
                                mli = LIST_FIRST(&mli_head);
                                genid = mld_mli_list_genid;
                        } else {
                                mli = LIST_NEXT(mli, mli_link);
                        }
                }

                LIST_FOREACH(mli, &mli_head, mli_link)
                mli->mli_flags &= ~MLIF_PROCESSED;
        }



        if (!current_state_timers_running6 &&
            !state_change_timers_running6) {
                goto out_locked;
        }

        current_state_timers_running6 = 0;
        state_change_timers_running6 = 0;

        MLD_PRINTF(("%s: state change timers running\n", __func__));

        memset(&qrq, 0, sizeof(struct ifqueue));
        qrq.ifq_maxlen = MLD_MAX_G_GS_PACKETS;

        memset(&scq, 0, sizeof(struct ifqueue));
        scq.ifq_maxlen = MLD_MAX_STATE_CHANGE_PACKETS;

        /*
         * MLD host report and state-change timer processing.
         * Note: Processing a v2 group timer may remove a node.
         */
        mli = LIST_FIRST(&mli_head);

        while (mli != NULL) {
                struct in6_multistep step;

                if (mli->mli_flags & MLIF_PROCESSED) {
                        mli = LIST_NEXT(mli, mli_link);
                        continue;
                }

                MLI_LOCK(mli);
                ifp = mli->mli_ifp;
                uri_sec = MLD_RANDOM_DELAY(mli->mli_uri);
                MLI_UNLOCK(mli);

                in6_multihead_lock_shared();
                IN6_FIRST_MULTI(step, inm);
                while (inm != NULL) {
                        IN6M_LOCK(inm);
                        if (inm->in6m_ifp != ifp) {
                                goto next;
                        }

                        MLI_LOCK(mli);
                        switch (mli->mli_version) {
                        case MLD_VERSION_1:
                                mld_v1_process_group_timer(inm,
                                    mli->mli_version);
                                break;
                        case MLD_VERSION_2:
                                mld_v2_process_group_timers(mli, &qrq,
                                    &scq, inm, uri_sec);
                                break;
                        }
                        MLI_UNLOCK(mli);
next:
                        IN6M_UNLOCK(inm);
                        IN6_NEXT_MULTI(step, inm);
                }
                in6_multihead_lock_done();

                /*
                 * XXX The logic below ends up calling
                 * mld_dispatch_packet which can unlock mli
                 * and the global MLD lock.
                 * Therefore grab a reference on MLI and also
                 * check for generation count to see if we should
                 * iterate the list again.
                 */
                MLI_LOCK(mli);
                MLI_ADDREF_LOCKED(mli);
                if (mli->mli_version == MLD_VERSION_1) {
                        mld_dispatch_queue_locked(mli, &mli->mli_v1q, 0);
                } else if (mli->mli_version == MLD_VERSION_2) {
                        MLI_UNLOCK(mli);
                        mld_dispatch_queue_locked(NULL, &qrq, 0);
                        mld_dispatch_queue_locked(NULL, &scq, 0);
                        VERIFY(qrq.ifq_len == 0);
                        VERIFY(scq.ifq_len == 0);
                        MLI_LOCK(mli);
                }
                /*
                 * In case there are still any pending membership reports
                 * which didn't get drained at version change time.
                 */
                IF_DRAIN(&mli->mli_v1q);
                /*
                 * Release all deferred inm records, and drain any locally
                 * enqueued packets; do it even if the current MLD version
                 * for the link is no longer MLDv2, in order to handle the
                 * version change case.
                 */
                mld_flush_relq(mli, (struct mld_in6m_relhead *)&in6m_dthead);
                VERIFY(SLIST_EMPTY(&mli->mli_relinmhead));
                mli->mli_flags |= MLIF_PROCESSED;
                MLI_UNLOCK(mli);
                MLI_REMREF(mli);

                IF_DRAIN(&qrq);
                IF_DRAIN(&scq);

                if (genid != mld_mli_list_genid) {
                        MLD_PRINTF(("%s: MLD information list changed "
                            "in the middle of iteration! Restart iteration.\n",
                            __func__));
                        mli = LIST_FIRST(&mli_head);
                        genid = mld_mli_list_genid;
                } else {
                        mli = LIST_NEXT(mli, mli_link);
                }
        }

        LIST_FOREACH(mli, &mli_head, mli_link)
        mli->mli_flags &= ~MLIF_PROCESSED;

out_locked:
        /* re-arm the timer if there's work to do */
        mld_timeout_run = 0;
        mld_sched_timeout();
        MLD_UNLOCK();

        /* Now that we're dropped all locks, release detached records */
        MLD_REMOVE_DETACHED_IN6M(&in6m_dthead);
}

static void
mld_sched_timeout(void)
{
        MLD_LOCK_ASSERT_HELD();

        if (!mld_timeout_run &&
            (querier_present_timers_running6 || current_state_timers_running6 ||
            interface_timers_running6 || state_change_timers_running6)) {
                mld_timeout_run = 1;
                timeout(mld_timeout, NULL, hz);
        }
}

/*
 * Free the in6_multi reference(s) for this MLD lifecycle.
 *
 * Caller must be holding mli_lock.
 */
static void
mld_flush_relq(struct mld_ifinfo *mli, struct mld_in6m_relhead *in6m_dthead)
{
        struct in6_multi *inm;

again:
        MLI_LOCK_ASSERT_HELD(mli);
        inm = SLIST_FIRST(&mli->mli_relinmhead);
        if (inm != NULL) {
                int lastref;

                SLIST_REMOVE_HEAD(&mli->mli_relinmhead, in6m_nrele);
                MLI_UNLOCK(mli);

                in6_multihead_lock_exclusive();
                IN6M_LOCK(inm);
                VERIFY(inm->in6m_nrelecnt != 0);
                inm->in6m_nrelecnt--;
                lastref = in6_multi_detach(inm);
                VERIFY(!lastref || (!(inm->in6m_debug & IFD_ATTACHED) &&
                    inm->in6m_reqcnt == 0));
                IN6M_UNLOCK(inm);
                in6_multihead_lock_done();
                /* from mli_relinmhead */
                IN6M_REMREF(inm);
                /* from in6_multihead_list */
                if (lastref) {
                        /*
                         * Defer releasing our final reference, as we
                         * are holding the MLD lock at this point, and
                         * we could end up with locking issues later on
                         * (while issuing SIOCDELMULTI) when this is the
                         * final reference count.  Let the caller do it
                         * when it is safe.
                         */
                        MLD_ADD_DETACHED_IN6M(in6m_dthead, inm);
                }
                MLI_LOCK(mli);
                goto again;
        }
}

/*
 * Update host report group timer.
 * Will update the global pending timer flags.
 */
static void
mld_v1_process_group_timer(struct in6_multi *inm, const int mld_version)
{
#pragma unused(mld_version)
        int report_timer_expired;

        MLD_LOCK_ASSERT_HELD();
        IN6M_LOCK_ASSERT_HELD(inm);
        MLI_LOCK_ASSERT_HELD(inm->in6m_mli);

        if (inm->in6m_timer == 0) {
                report_timer_expired = 0;
        } else if (--inm->in6m_timer == 0) {
                report_timer_expired = 1;
        } else {
                current_state_timers_running6 = 1;
                /* caller will schedule timer */
                return;
        }

        switch (inm->in6m_state) {
        case MLD_NOT_MEMBER:
        case MLD_SILENT_MEMBER:
        case MLD_IDLE_MEMBER:
        case MLD_LAZY_MEMBER:
        case MLD_SLEEPING_MEMBER:
        case MLD_AWAKENING_MEMBER:
                break;
        case MLD_REPORTING_MEMBER:
                if (report_timer_expired) {
                        inm->in6m_state = MLD_IDLE_MEMBER;
                        (void) mld_v1_transmit_report(inm,
                            MLD_LISTENER_REPORT);
                        IN6M_LOCK_ASSERT_HELD(inm);
                        MLI_LOCK_ASSERT_HELD(inm->in6m_mli);
                }
                break;
        case MLD_G_QUERY_PENDING_MEMBER:
        case MLD_SG_QUERY_PENDING_MEMBER:
        case MLD_LEAVING_MEMBER:
                break;
        }
}

/*
 * Update a group's timers for MLDv2.
 * Will update the global pending timer flags.
 * Note: Unlocked read from mli.
 */
static void
mld_v2_process_group_timers(struct mld_ifinfo *mli,
    struct ifqueue *qrq, struct ifqueue *scq,
    struct in6_multi *inm, const int uri_sec)
{
        int query_response_timer_expired;
        int state_change_retransmit_timer_expired;

        MLD_LOCK_ASSERT_HELD();
        IN6M_LOCK_ASSERT_HELD(inm);
        MLI_LOCK_ASSERT_HELD(mli);
        VERIFY(mli == inm->in6m_mli);

        query_response_timer_expired = 0;
        state_change_retransmit_timer_expired = 0;

        /*
         * During a transition from compatibility mode back to MLDv2,
         * a group record in REPORTING state may still have its group
         * timer active. This is a no-op in this function; it is easier
         * to deal with it here than to complicate the timeout path.
         */
        if (inm->in6m_timer == 0) {
                query_response_timer_expired = 0;
        } else if (--inm->in6m_timer == 0) {
                query_response_timer_expired = 1;
        } else {
                current_state_timers_running6 = 1;
                /* caller will schedule timer */
        }

        if (inm->in6m_sctimer == 0) {
                state_change_retransmit_timer_expired = 0;
        } else if (--inm->in6m_sctimer == 0) {
                state_change_retransmit_timer_expired = 1;
        } else {
                state_change_timers_running6 = 1;
                /* caller will schedule timer */
        }

        /* We are in timer callback, so be quick about it. */
        if (!state_change_retransmit_timer_expired &&
            !query_response_timer_expired) {
                return;
        }

        switch (inm->in6m_state) {
        case MLD_NOT_MEMBER:
        case MLD_SILENT_MEMBER:
        case MLD_SLEEPING_MEMBER:
        case MLD_LAZY_MEMBER:
        case MLD_AWAKENING_MEMBER:
        case MLD_IDLE_MEMBER:
                break;
        case MLD_G_QUERY_PENDING_MEMBER:
        case MLD_SG_QUERY_PENDING_MEMBER:
                /*
                 * Respond to a previously pending Group-Specific
                 * or Group-and-Source-Specific query by enqueueing
                 * the appropriate Current-State report for
                 * immediate transmission.
                 */
                if (query_response_timer_expired) {
                        int retval;

                        retval = mld_v2_enqueue_group_record(qrq, inm, 0, 1,
                            (inm->in6m_state == MLD_SG_QUERY_PENDING_MEMBER),
                            0);
                        MLD_PRINTF(("%s: enqueue record = %d\n",
                            __func__, retval));
                        inm->in6m_state = MLD_REPORTING_MEMBER;
                        in6m_clear_recorded(inm);
                }
        /* FALLTHROUGH */
        case MLD_REPORTING_MEMBER:
        case MLD_LEAVING_MEMBER:
                if (state_change_retransmit_timer_expired) {
                        /*
                         * State-change retransmission timer fired.
                         * If there are any further pending retransmissions,
                         * set the global pending state-change flag, and
                         * reset the timer.
                         */
                        if (--inm->in6m_scrv > 0) {
                                inm->in6m_sctimer = uri_sec;
                                state_change_timers_running6 = 1;
                                /* caller will schedule timer */
                        }
                        /*
                         * Retransmit the previously computed state-change
                         * report. If there are no further pending
                         * retransmissions, the mbuf queue will be consumed.
                         * Update T0 state to T1 as we have now sent
                         * a state-change.
                         */
                        (void) mld_v2_merge_state_changes(inm, scq);

                        in6m_commit(inm);
                        MLD_PRINTF(("%s: T1 -> T0 for %s/%s\n", __func__,
                            ip6_sprintf(&inm->in6m_addr),
                            if_name(inm->in6m_ifp)));

                        /*
                         * If we are leaving the group for good, make sure
                         * we release MLD's reference to it.
                         * This release must be deferred using a SLIST,
                         * as we are called from a loop which traverses
                         * the in_ifmultiaddr TAILQ.
                         */
                        if (inm->in6m_state == MLD_LEAVING_MEMBER &&
                            inm->in6m_scrv == 0) {
                                inm->in6m_state = MLD_NOT_MEMBER;
                                /*
                                 * A reference has already been held in
                                 * mld_final_leave() for this inm, so
                                 * no need to hold another one.  We also
                                 * bumped up its request count then, so
                                 * that it stays in in6_multihead.  Both
                                 * of them will be released when it is
                                 * dequeued later on.
                                 */
                                VERIFY(inm->in6m_nrelecnt != 0);
                                SLIST_INSERT_HEAD(&mli->mli_relinmhead,
                                    inm, in6m_nrele);
                        }
                }
                break;
        }
}

/*
 * Switch to a different version on the given interface,
 * as per Section 9.12.
 */
static uint32_t
mld_set_version(struct mld_ifinfo *mli, const int mld_version)
{
        int old_version_timer;

        MLI_LOCK_ASSERT_HELD(mli);

        MLD_PRINTF(("%s: switching to v%d on ifp 0x%llx(%s)\n", __func__,
            mld_version, (uint64_t)VM_KERNEL_ADDRPERM(mli->mli_ifp),
            if_name(mli->mli_ifp)));

        if (mld_version == MLD_VERSION_1) {
                /*
                 * Compute the "Older Version Querier Present" timer as per
                 * Section 9.12, in seconds.
                 */
                old_version_timer = (mli->mli_rv * mli->mli_qi) + mli->mli_qri;
                mli->mli_v1_timer = old_version_timer;
        }

        if (mli->mli_v1_timer > 0 && mli->mli_version != MLD_VERSION_1) {
                mli->mli_version = MLD_VERSION_1;
                mld_v2_cancel_link_timers(mli);
        }

        MLI_LOCK_ASSERT_HELD(mli);

        return mli->mli_v1_timer;
}

/*
 * Cancel pending MLDv2 timers for the given link and all groups
 * joined on it; state-change, general-query, and group-query timers.
 *
 * Only ever called on a transition from v2 to Compatibility mode. Kill
 * the timers stone dead (this may be expensive for large N groups), they
 * will be restarted if Compatibility Mode deems that they must be due to
 * query processing.
 */
static void
mld_v2_cancel_link_timers(struct mld_ifinfo *mli)
{
        struct ifnet            *ifp;
        struct in6_multi        *inm;
        struct in6_multistep    step;

        MLI_LOCK_ASSERT_HELD(mli);

        MLD_PRINTF(("%s: cancel v2 timers on ifp 0x%llx(%s)\n", __func__,
            (uint64_t)VM_KERNEL_ADDRPERM(mli->mli_ifp), if_name(mli->mli_ifp)));

        /*
         * Stop the v2 General Query Response on this link stone dead.
         * If timer is woken up due to interface_timers_running6,
         * the flag will be cleared if there are no pending link timers.
         */
        mli->mli_v2_timer = 0;

        /*
         * Now clear the current-state and state-change report timers
         * for all memberships scoped to this link.
         */
        ifp = mli->mli_ifp;
        MLI_UNLOCK(mli);

        in6_multihead_lock_shared();
        IN6_FIRST_MULTI(step, inm);
        while (inm != NULL) {
                IN6M_LOCK(inm);
                if (inm->in6m_ifp != ifp) {
                        goto next;
                }

                switch (inm->in6m_state) {
                case MLD_NOT_MEMBER:
                case MLD_SILENT_MEMBER:
                case MLD_IDLE_MEMBER:
                case MLD_LAZY_MEMBER:
                case MLD_SLEEPING_MEMBER:
                case MLD_AWAKENING_MEMBER:
                        /*
                         * These states are either not relevant in v2 mode,
                         * or are unreported. Do nothing.
                         */
                        break;
                case MLD_LEAVING_MEMBER:
                        /*
                         * If we are leaving the group and switching
                         * version, we need to release the final
                         * reference held for issuing the INCLUDE {}.
                         * During mld_final_leave(), we bumped up both the
                         * request and reference counts.  Since we cannot
                         * call in6_multi_detach() here, defer this task to
                         * the timer routine.
                         */
                        VERIFY(inm->in6m_nrelecnt != 0);
                        MLI_LOCK(mli);
                        SLIST_INSERT_HEAD(&mli->mli_relinmhead, inm,
                            in6m_nrele);
                        MLI_UNLOCK(mli);
                /* FALLTHROUGH */
                case MLD_G_QUERY_PENDING_MEMBER:
                case MLD_SG_QUERY_PENDING_MEMBER:
                        in6m_clear_recorded(inm);
                /* FALLTHROUGH */
                case MLD_REPORTING_MEMBER:
                        inm->in6m_state = MLD_REPORTING_MEMBER;
                        break;
                }
                /*
                 * Always clear state-change and group report timers.
                 * Free any pending MLDv2 state-change records.
                 */
                inm->in6m_sctimer = 0;
                inm->in6m_timer = 0;
                IF_DRAIN(&inm->in6m_scq);
next:
                IN6M_UNLOCK(inm);
                IN6_NEXT_MULTI(step, inm);
        }
        in6_multihead_lock_done();

        MLI_LOCK(mli);
}

/*
 * Update the Older Version Querier Present timers for a link.
 * See Section 9.12 of RFC 3810.
 */
static void
mld_v1_process_querier_timers(struct mld_ifinfo *mli)
{
        MLI_LOCK_ASSERT_HELD(mli);

        if (mld_v2enable && mli->mli_version != MLD_VERSION_2 &&
            --mli->mli_v1_timer == 0) {
                /*
                 * MLDv1 Querier Present timer expired; revert to MLDv2.
                 */
                MLD_PRINTF(("%s: transition from v%d -> v%d on 0x%llx(%s)\n",
                    __func__, mli->mli_version, MLD_VERSION_2,
                    (uint64_t)VM_KERNEL_ADDRPERM(mli->mli_ifp),
                    if_name(mli->mli_ifp)));
                mli->mli_version = MLD_VERSION_2;
        }
}

/*
 * Transmit an MLDv1 report immediately.
 */
static int
mld_v1_transmit_report(struct in6_multi *in6m, const int type)
{
        struct ifnet            *ifp;
        struct in6_ifaddr       *ia;
        struct ip6_hdr          *ip6;
        struct mbuf             *mh, *md;
        struct mld_hdr          *mld;
        int                     error = 0;

        IN6M_LOCK_ASSERT_HELD(in6m);
        MLI_LOCK_ASSERT_HELD(in6m->in6m_mli);

        ifp = in6m->in6m_ifp;
        /* ia may be NULL if link-local address is tentative. */
        ia = in6ifa_ifpforlinklocal(ifp, IN6_IFF_NOTREADY | IN6_IFF_ANYCAST);

        MGETHDR(mh, M_DONTWAIT, MT_HEADER);
        if (mh == NULL) {
                if (ia != NULL) {
                        IFA_REMREF(&ia->ia_ifa);
                }
                return ENOMEM;
        }
        MGET(md, M_DONTWAIT, MT_DATA);
        if (md == NULL) {
                m_free(mh);
                if (ia != NULL) {
                        IFA_REMREF(&ia->ia_ifa);
                }
                return ENOMEM;
        }
        mh->m_next = md;

        /*
         * FUTURE: Consider increasing alignment by ETHER_HDR_LEN, so
         * that ether_output() does not need to allocate another mbuf
         * for the header in the most common case.
         */
        MH_ALIGN(mh, sizeof(struct ip6_hdr));
        mh->m_pkthdr.len = sizeof(struct ip6_hdr) + sizeof(struct mld_hdr);
        mh->m_len = sizeof(struct ip6_hdr);

        ip6 = mtod(mh, struct ip6_hdr *);
        ip6->ip6_flow = 0;
        ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
        ip6->ip6_vfc |= IPV6_VERSION;
        ip6->ip6_nxt = IPPROTO_ICMPV6;
        if (ia != NULL) {
                IFA_LOCK(&ia->ia_ifa);
        }
        ip6->ip6_src = ia ? ia->ia_addr.sin6_addr : in6addr_any;
        if (ia != NULL) {
                IFA_UNLOCK(&ia->ia_ifa);
                IFA_REMREF(&ia->ia_ifa);
                ia = NULL;
        }
        ip6->ip6_dst = in6m->in6m_addr;

        md->m_len = sizeof(struct mld_hdr);
        mld = mtod(md, struct mld_hdr *);
        mld->mld_type = type;
        mld->mld_code = 0;
        mld->mld_cksum = 0;
        mld->mld_maxdelay = 0;
        mld->mld_reserved = 0;
        mld->mld_addr = in6m->in6m_addr;
        in6_clearscope(&mld->mld_addr);
        mld->mld_cksum = in6_cksum(mh, IPPROTO_ICMPV6,
            sizeof(struct ip6_hdr), sizeof(struct mld_hdr));

        mld_save_context(mh, ifp);
        mh->m_flags |= M_MLDV1;

        /*
         * Due to the fact that at this point we are possibly holding
         * in6_multihead_lock in shared or exclusive mode, we can't call
         * mld_dispatch_packet() here since that will eventually call
         * ip6_output(), which will try to lock in6_multihead_lock and cause
         * a deadlock.
         * Instead we defer the work to the mld_timeout() thread, thus
         * avoiding unlocking in_multihead_lock here.
         */
        if (IF_QFULL(&in6m->in6m_mli->mli_v1q)) {
                MLD_PRINTF(("%s: v1 outbound queue full\n", __func__));
                error = ENOMEM;
                m_freem(mh);
        } else {
                IF_ENQUEUE(&in6m->in6m_mli->mli_v1q, mh);
                VERIFY(error == 0);
        }

        return error;
}

/*
 * Process a state change from the upper layer for the given IPv6 group.
 *
 * Each socket holds a reference on the in6_multi in its own ip_moptions.
 * The socket layer will have made the necessary updates to.the group
 * state, it is now up to MLD to issue a state change report if there
 * has been any change between T0 (when the last state-change was issued)
 * and T1 (now).
 *
 * We use the MLDv2 state machine at group level. The MLd module
 * however makes the decision as to which MLD protocol version to speak.
 * A state change *from* INCLUDE {} always means an initial join.
 * A state change *to* INCLUDE {} always means a final leave.
 *
 * If delay is non-zero, and the state change is an initial multicast
 * join, the state change report will be delayed by 'delay' ticks
 * in units of seconds if MLDv1 is active on the link; otherwise
 * the initial MLDv2 state change report will be delayed by whichever
 * is sooner, a pending state-change timer or delay itself.
 */
int
mld_change_state(struct in6_multi *inm, struct mld_tparams *mtp,
    const int delay)
{
        struct mld_ifinfo *mli;
        struct ifnet *ifp;
        int error = 0;

        VERIFY(mtp != NULL);
        bzero(mtp, sizeof(*mtp));

        IN6M_LOCK_ASSERT_HELD(inm);
        VERIFY(inm->in6m_mli != NULL);
        MLI_LOCK_ASSERT_NOTHELD(inm->in6m_mli);

        /*
         * Try to detect if the upper layer just asked us to change state
         * for an interface which has now gone away.
         */
        VERIFY(inm->in6m_ifma != NULL);
        ifp = inm->in6m_ifma->ifma_ifp;
        /*
         * Sanity check that netinet6's notion of ifp is the same as net's.
         */
        VERIFY(inm->in6m_ifp == ifp);

        mli = MLD_IFINFO(ifp);
        VERIFY(mli != NULL);

        /*
         * If we detect a state transition to or from MCAST_UNDEFINED
         * for this group, then we are starting or finishing an MLD
         * life cycle for this group.
         */
        if (inm->in6m_st[1].iss_fmode != inm->in6m_st[0].iss_fmode) {
                MLD_PRINTF(("%s: inm transition %d -> %d\n", __func__,
                    inm->in6m_st[0].iss_fmode, inm->in6m_st[1].iss_fmode));
                if (inm->in6m_st[0].iss_fmode == MCAST_UNDEFINED) {
                        MLD_PRINTF(("%s: initial join\n", __func__));
                        error = mld_initial_join(inm, mli, mtp, delay);
                        goto out;
                } else if (inm->in6m_st[1].iss_fmode == MCAST_UNDEFINED) {
                        MLD_PRINTF(("%s: final leave\n", __func__));
                        mld_final_leave(inm, mli, mtp);
                        goto out;
                }
        } else {
                MLD_PRINTF(("%s: filter set change\n", __func__));
        }

        error = mld_handle_state_change(inm, mli, mtp);
out:
        return error;
}

/*
 * Perform the initial join for an MLD group.
 *
 * When joining a group:
 *  If the group should have its MLD traffic suppressed, do nothing.
 *  MLDv1 starts sending MLDv1 host membership reports.
 *  MLDv2 will schedule an MLDv2 state-change report containing the
 *  initial state of the membership.
 *
 * If the delay argument is non-zero, then we must delay sending the
 * initial state change for delay ticks (in units of seconds).
 */
static int
mld_initial_join(struct in6_multi *inm, struct mld_ifinfo *mli,
    struct mld_tparams *mtp, const int delay)
{
        struct ifnet            *ifp;
        struct ifqueue          *ifq;
        int                      error, retval, syncstates;
        int                      odelay;

        IN6M_LOCK_ASSERT_HELD(inm);
        MLI_LOCK_ASSERT_NOTHELD(mli);
        VERIFY(mtp != NULL);

        MLD_PRINTF(("%s: initial join %s on ifp 0x%llx(%s)\n",
            __func__, ip6_sprintf(&inm->in6m_addr),
            (uint64_t)VM_KERNEL_ADDRPERM(inm->in6m_ifp),
            if_name(inm->in6m_ifp)));

        error = 0;
        syncstates = 1;

        ifp = inm->in6m_ifp;

        MLI_LOCK(mli);
        VERIFY(mli->mli_ifp == ifp);

        /*
         * Avoid MLD if group is :
         * 1. Joined on loopback, OR
         * 2. On a link that is marked MLIF_SILENT
         * 3. rdar://problem/19227650 Is link local scoped and
         *    on cellular interface
         * 4. Is a type that should not be reported (node local
         *    or all node link local multicast.
         * All other groups enter the appropriate state machine
         * for the version in use on this link.
         */
        if ((ifp->if_flags & IFF_LOOPBACK) ||
            (mli->mli_flags & MLIF_SILENT) ||
            (IFNET_IS_CELLULAR(ifp) &&
            IN6_IS_ADDR_MC_LINKLOCAL(&inm->in6m_addr)) ||
            !mld_is_addr_reported(&inm->in6m_addr)) {
                MLD_PRINTF(("%s: not kicking state machine for silent group\n",
                    __func__));
                inm->in6m_state = MLD_SILENT_MEMBER;
                inm->in6m_timer = 0;
        } else {
                /*
                 * Deal with overlapping in6_multi lifecycle.
                 * If this group was LEAVING, then make sure
                 * we drop the reference we picked up to keep the
                 * group around for the final INCLUDE {} enqueue.
                 * Since we cannot call in6_multi_detach() here,
                 * defer this task to the timer routine.
                 */
                if (mli->mli_version == MLD_VERSION_2 &&
                    inm->in6m_state == MLD_LEAVING_MEMBER) {
                        VERIFY(inm->in6m_nrelecnt != 0);
                        SLIST_INSERT_HEAD(&mli->mli_relinmhead, inm,
                            in6m_nrele);
                }

                inm->in6m_state = MLD_REPORTING_MEMBER;

                switch (mli->mli_version) {
                case MLD_VERSION_1:
                        /*
                         * If a delay was provided, only use it if
                         * it is greater than the delay normally
                         * used for an MLDv1 state change report,
                         * and delay sending the initial MLDv1 report
                         * by not transitioning to the IDLE state.
                         */
                        odelay = MLD_RANDOM_DELAY(MLD_V1_MAX_RI);
                        if (delay) {
                                inm->in6m_timer = max(delay, odelay);
                                mtp->cst = 1;
                        } else {
                                inm->in6m_state = MLD_IDLE_MEMBER;
                                error = mld_v1_transmit_report(inm,
                                    MLD_LISTENER_REPORT);

                                IN6M_LOCK_ASSERT_HELD(inm);
                                MLI_LOCK_ASSERT_HELD(mli);

                                if (error == 0) {
                                        inm->in6m_timer = odelay;
                                        mtp->cst = 1;
                                }
                        }
                        break;

                case MLD_VERSION_2:
                        /*
                         * Defer update of T0 to T1, until the first copy
                         * of the state change has been transmitted.
                         */
                        syncstates = 0;

                        /*
                         * Immediately enqueue a State-Change Report for
                         * this interface, freeing any previous reports.
                         * Don't kick the timers if there is nothing to do,
                         * or if an error occurred.
                         */
                        ifq = &inm->in6m_scq;
                        IF_DRAIN(ifq);
                        retval = mld_v2_enqueue_group_record(ifq, inm, 1,
                            0, 0, (mli->mli_flags & MLIF_USEALLOW));
                        mtp->cst = (ifq->ifq_len > 0);
                        MLD_PRINTF(("%s: enqueue record = %d\n",
                            __func__, retval));
                        if (retval <= 0) {
                                error = retval * -1;
                                break;
                        }

                        /*
                         * Schedule transmission of pending state-change
                         * report up to RV times for this link. The timer
                         * will fire at the next mld_timeout (1 second)),
                         * giving us an opportunity to merge the reports.
                         *
                         * If a delay was provided to this function, only
                         * use this delay if sooner than the existing one.
                         */
                        VERIFY(mli->mli_rv > 1);
                        inm->in6m_scrv = mli->mli_rv;
                        if (delay) {
                                if (inm->in6m_sctimer > 1) {
                                        inm->in6m_sctimer =
                                            min(inm->in6m_sctimer, delay);
                                } else {
                                        inm->in6m_sctimer = delay;
                                }
                        } else {
                                inm->in6m_sctimer = 1;
                        }
                        mtp->sct = 1;
                        error = 0;
                        break;
                }
        }
        MLI_UNLOCK(mli);

        /*
         * Only update the T0 state if state change is atomic,
         * i.e. we don't need to wait for a timer to fire before we
         * can consider the state change to have been communicated.
         */
        if (syncstates) {
                in6m_commit(inm);
                MLD_PRINTF(("%s: T1 -> T0 for %s/%s\n", __func__,
                    ip6_sprintf(&inm->in6m_addr),
                    if_name(inm->in6m_ifp)));
        }

        return error;
}

/*
 * Issue an intermediate state change during the life-cycle.
 */
static int
mld_handle_state_change(struct in6_multi *inm, struct mld_ifinfo *mli,
    struct mld_tparams *mtp)
{
        struct ifnet            *ifp;
        int                      retval = 0;

        IN6M_LOCK_ASSERT_HELD(inm);
        MLI_LOCK_ASSERT_NOTHELD(mli);
        VERIFY(mtp != NULL);

        MLD_PRINTF(("%s: state change for %s on ifp 0x%llx(%s)\n",
            __func__, ip6_sprintf(&inm->in6m_addr),
            (uint64_t)VM_KERNEL_ADDRPERM(inm->in6m_ifp),
            if_name(inm->in6m_ifp)));

        ifp = inm->in6m_ifp;

        MLI_LOCK(mli);
        VERIFY(mli->mli_ifp == ifp);

        if ((ifp->if_flags & IFF_LOOPBACK) ||
            (mli->mli_flags & MLIF_SILENT) ||
            !mld_is_addr_reported(&inm->in6m_addr) ||
            (mli->mli_version != MLD_VERSION_2)) {
                MLI_UNLOCK(mli);
                if (!mld_is_addr_reported(&inm->in6m_addr)) {
                        MLD_PRINTF(("%s: not kicking state machine for silent "
                            "group\n", __func__));
                }
                MLD_PRINTF(("%s: nothing to do\n", __func__));
                in6m_commit(inm);
                MLD_PRINTF(("%s: T1 -> T0 for %s/%s\n", __func__,
                    ip6_sprintf(&inm->in6m_addr),
                    if_name(inm->in6m_ifp)));
                goto done;
        }

        IF_DRAIN(&inm->in6m_scq);

        retval = mld_v2_enqueue_group_record(&inm->in6m_scq, inm, 1, 0, 0,
            (mli->mli_flags & MLIF_USEALLOW));
        mtp->cst = (inm->in6m_scq.ifq_len > 0);
        MLD_PRINTF(("%s: enqueue record = %d\n", __func__, retval));
        if (retval <= 0) {
                MLI_UNLOCK(mli);
                retval *= -1;
                goto done;
        } else {
                retval = 0;
        }

        /*
         * If record(s) were enqueued, start the state-change
         * report timer for this group.
         */
        inm->in6m_scrv = mli->mli_rv;
        inm->in6m_sctimer = 1;
        mtp->sct = 1;
        MLI_UNLOCK(mli);

done:
        return retval;
}

/*
 * Perform the final leave for a multicast address.
 *
 * When leaving a group:
 *  MLDv1 sends a DONE message, if and only if we are the reporter.
 *  MLDv2 enqueues a state-change report containing a transition
 *  to INCLUDE {} for immediate transmission.
 */
static void
mld_final_leave(struct in6_multi *inm, struct mld_ifinfo *mli,
    struct mld_tparams *mtp)
{
        int syncstates = 1;

        IN6M_LOCK_ASSERT_HELD(inm);
        MLI_LOCK_ASSERT_NOTHELD(mli);
        VERIFY(mtp != NULL);

        MLD_PRINTF(("%s: final leave %s on ifp 0x%llx(%s)\n",
            __func__, ip6_sprintf(&inm->in6m_addr),
            (uint64_t)VM_KERNEL_ADDRPERM(inm->in6m_ifp),
            if_name(inm->in6m_ifp)));

        switch (inm->in6m_state) {
        case MLD_NOT_MEMBER:
        case MLD_SILENT_MEMBER:
        case MLD_LEAVING_MEMBER:
                /* Already leaving or left; do nothing. */
                MLD_PRINTF(("%s: not kicking state machine for silent group\n",
                    __func__));
                break;
        case MLD_REPORTING_MEMBER:
        case MLD_IDLE_MEMBER:
        case MLD_G_QUERY_PENDING_MEMBER:
        case MLD_SG_QUERY_PENDING_MEMBER:
                MLI_LOCK(mli);
                if (mli->mli_version == MLD_VERSION_1) {
                        if (inm->in6m_state == MLD_G_QUERY_PENDING_MEMBER ||
                            inm->in6m_state == MLD_SG_QUERY_PENDING_MEMBER) {
                                panic("%s: MLDv2 state reached, not MLDv2 "
                                    "mode\n", __func__);
                                /* NOTREACHED */
                        }
                        /* scheduler timer if enqueue is successful */
                        mtp->cst = (mld_v1_transmit_report(inm,
                            MLD_LISTENER_DONE) == 0);

                        IN6M_LOCK_ASSERT_HELD(inm);
                        MLI_LOCK_ASSERT_HELD(mli);

                        inm->in6m_state = MLD_NOT_MEMBER;
                } else if (mli->mli_version == MLD_VERSION_2) {
                        /*
                         * Stop group timer and all pending reports.
                         * Immediately enqueue a state-change report
                         * TO_IN {} to be sent on the next timeout,
                         * giving us an opportunity to merge reports.
                         */
                        IF_DRAIN(&inm->in6m_scq);
                        inm->in6m_timer = 0;
                        inm->in6m_scrv = mli->mli_rv;
                        MLD_PRINTF(("%s: Leaving %s/%s with %d "
                            "pending retransmissions.\n", __func__,
                            ip6_sprintf(&inm->in6m_addr),
                            if_name(inm->in6m_ifp),
                            inm->in6m_scrv));
                        if (inm->in6m_scrv == 0) {
                                inm->in6m_state = MLD_NOT_MEMBER;
                                inm->in6m_sctimer = 0;
                        } else {
                                int retval;
                                /*
                                 * Stick around in the in6_multihead list;
                                 * the final detach will be issued by
                                 * mld_v2_process_group_timers() when
                                 * the retransmit timer expires.
                                 */
                                IN6M_ADDREF_LOCKED(inm);
                                VERIFY(inm->in6m_debug & IFD_ATTACHED);
                                inm->in6m_reqcnt++;
                                VERIFY(inm->in6m_reqcnt >= 1);
                                inm->in6m_nrelecnt++;
                                VERIFY(inm->in6m_nrelecnt != 0);

                                retval = mld_v2_enqueue_group_record(
                                        &inm->in6m_scq, inm, 1, 0, 0,
                                        (mli->mli_flags & MLIF_USEALLOW));
                                mtp->cst = (inm->in6m_scq.ifq_len > 0);
                                KASSERT(retval != 0,
                                    ("%s: enqueue record = %d\n", __func__,
                                    retval));

                                inm->in6m_state = MLD_LEAVING_MEMBER;
                                inm->in6m_sctimer = 1;
                                mtp->sct = 1;
                                syncstates = 0;
                        }
                }
                MLI_UNLOCK(mli);
                break;
        case MLD_LAZY_MEMBER:
        case MLD_SLEEPING_MEMBER:
        case MLD_AWAKENING_MEMBER:
                /* Our reports are suppressed; do nothing. */
                break;
        }

        if (syncstates) {
                in6m_commit(inm);
                MLD_PRINTF(("%s: T1 -> T0 for %s/%s\n", __func__,
                    ip6_sprintf(&inm->in6m_addr),
                    if_name(inm->in6m_ifp)));
                inm->in6m_st[1].iss_fmode = MCAST_UNDEFINED;
                MLD_PRINTF(("%s: T1 now MCAST_UNDEFINED for 0x%llx/%s\n",
                    __func__, (uint64_t)VM_KERNEL_ADDRPERM(&inm->in6m_addr),
                    if_name(inm->in6m_ifp)));
        }
}

/*
 * Enqueue an MLDv2 group record to the given output queue.
 *
 * If is_state_change is zero, a current-state record is appended.
 * If is_state_change is non-zero, a state-change report is appended.
 *
 * If is_group_query is non-zero, an mbuf packet chain is allocated.
 * If is_group_query is zero, and if there is a packet with free space
 * at the tail of the queue, it will be appended to providing there
 * is enough free space.
 * Otherwise a new mbuf packet chain is allocated.
 *
 * If is_source_query is non-zero, each source is checked to see if
 * it was recorded for a Group-Source query, and will be omitted if
 * it is not both in-mode and recorded.
 *
 * If use_block_allow is non-zero, state change reports for initial join
 * and final leave, on an inclusive mode group with a source list, will be
 * rewritten to use the ALLOW_NEW and BLOCK_OLD record types, respectively.
 *
 * The function will attempt to allocate leading space in the packet
 * for the IPv6+ICMP headers to be prepended without fragmenting the chain.
 *
 * If successful the size of all data appended to the queue is returned,
 * otherwise an error code less than zero is returned, or zero if
 * no record(s) were appended.
 */
static int
mld_v2_enqueue_group_record(struct ifqueue *ifq, struct in6_multi *inm,
    const int is_state_change, const int is_group_query,
    const int is_source_query, const int use_block_allow)
{
        struct mldv2_record      mr;
        struct mldv2_record     *pmr;
        struct ifnet            *ifp;
        struct ip6_msource      *ims, *nims;
        struct mbuf             *m0, *m, *md;
        int                      error, is_filter_list_change;
        int                      minrec0len, m0srcs, msrcs, nbytes, off;
        int                      record_has_sources;
        int                      now;
        int                      type;
        uint8_t                  mode;

        IN6M_LOCK_ASSERT_HELD(inm);
        MLI_LOCK_ASSERT_HELD(inm->in6m_mli);

        error = 0;
        ifp = inm->in6m_ifp;
        is_filter_list_change = 0;
        m = NULL;
        m0 = NULL;
        m0srcs = 0;
        msrcs = 0;
        nbytes = 0;
        nims = NULL;
        record_has_sources = 1;
        pmr = NULL;
        type = MLD_DO_NOTHING;
        mode = inm->in6m_st[1].iss_fmode;

        /*
         * If we did not transition out of ASM mode during t0->t1,
         * and there are no source nodes to process, we can skip
         * the generation of source records.
         */
        if (inm->in6m_st[0].iss_asm > 0 && inm->in6m_st[1].iss_asm > 0 &&
            inm->in6m_nsrc == 0) {
                record_has_sources = 0;
        }

        if (is_state_change) {
                /*
                 * Queue a state change record.
                 * If the mode did not change, and there are non-ASM
                 * listeners or source filters present,
                 * we potentially need to issue two records for the group.
                 * If there are ASM listeners, and there was no filter
                 * mode transition of any kind, do nothing.
                 *
                 * If we are transitioning to MCAST_UNDEFINED, we need
                 * not send any sources. A transition to/from this state is
                 * considered inclusive with some special treatment.
                 *
                 * If we are rewriting initial joins/leaves to use
                 * ALLOW/BLOCK, and the group's membership is inclusive,
                 * we need to send sources in all cases.
                 */
                if (mode != inm->in6m_st[0].iss_fmode) {
                        if (mode == MCAST_EXCLUDE) {
                                MLD_PRINTF(("%s: change to EXCLUDE\n",
                                    __func__));
                                type = MLD_CHANGE_TO_EXCLUDE_MODE;
                        } else {
                                MLD_PRINTF(("%s: change to INCLUDE\n",
                                    __func__));
                                if (use_block_allow) {
                                        /*
                                         * XXX
                                         * Here we're interested in state
                                         * edges either direction between
                                         * MCAST_UNDEFINED and MCAST_INCLUDE.
                                         * Perhaps we should just check
                                         * the group state, rather than
                                         * the filter mode.
                                         */
                                        if (mode == MCAST_UNDEFINED) {
                                                type = MLD_BLOCK_OLD_SOURCES;
                                        } else {
                                                type = MLD_ALLOW_NEW_SOURCES;
                                        }
                                } else {
                                        type = MLD_CHANGE_TO_INCLUDE_MODE;
                                        if (mode == MCAST_UNDEFINED) {
                                                record_has_sources = 0;
                                        }
                                }
                        }
                } else {
                        if (record_has_sources) {
                                is_filter_list_change = 1;
                        } else {
                                type = MLD_DO_NOTHING;
                        }
                }
        } else {
                /*
                 * Queue a current state record.
                 */
                if (mode == MCAST_EXCLUDE) {
                        type = MLD_MODE_IS_EXCLUDE;
                } else if (mode == MCAST_INCLUDE) {
                        type = MLD_MODE_IS_INCLUDE;
                        VERIFY(inm->in6m_st[1].iss_asm == 0);
                }
        }

        /*
         * Generate the filter list changes using a separate function.
         */
        if (is_filter_list_change) {
                return mld_v2_enqueue_filter_change(ifq, inm);
        }

        if (type == MLD_DO_NOTHING) {
                MLD_PRINTF(("%s: nothing to do for %s/%s\n",
                    __func__, ip6_sprintf(&inm->in6m_addr),
                    if_name(inm->in6m_ifp)));
                return 0;
        }

        /*
         * If any sources are present, we must be able to fit at least
         * one in the trailing space of the tail packet's mbuf,
         * ideally more.
         */
        minrec0len = sizeof(struct mldv2_record);
        if (record_has_sources) {
                minrec0len += sizeof(struct in6_addr);
        }
        MLD_PRINTF(("%s: queueing %s for %s/%s\n", __func__,
            mld_rec_type_to_str(type),
            ip6_sprintf(&inm->in6m_addr),
            if_name(inm->in6m_ifp)));

        /*
         * Check if we have a packet in the tail of the queue for this
         * group into which the first group record for this group will fit.
         * Otherwise allocate a new packet.
         * Always allocate leading space for IP6+RA+ICMPV6+REPORT.
         * Note: Group records for G/GSR query responses MUST be sent
         * in their own packet.
         */
        m0 = ifq->ifq_tail;
        if (!is_group_query &&
            m0 != NULL &&
            (m0->m_pkthdr.vt_nrecs + 1 <= MLD_V2_REPORT_MAXRECS) &&
            (m0->m_pkthdr.len + minrec0len) <
            (ifp->if_mtu - MLD_MTUSPACE)) {
                m0srcs = (ifp->if_mtu - m0->m_pkthdr.len -
                    sizeof(struct mldv2_record)) /
                    sizeof(struct in6_addr);
                m = m0;
                MLD_PRINTF(("%s: use existing packet\n", __func__));
        } else {
                if (IF_QFULL(ifq)) {
                        MLD_PRINTF(("%s: outbound queue full\n", __func__));
                        return -ENOMEM;
                }
                m = NULL;
                m0srcs = (ifp->if_mtu - MLD_MTUSPACE -
                    sizeof(struct mldv2_record)) / sizeof(struct in6_addr);
                if (!is_state_change && !is_group_query) {
                        m = m_getcl(M_DONTWAIT, MT_DATA, M_PKTHDR);
                }
                if (m == NULL) {
                        m = m_gethdr(M_DONTWAIT, MT_DATA);
                }
                if (m == NULL) {
                        return -ENOMEM;
                }

                mld_save_context(m, ifp);

                MLD_PRINTF(("%s: allocated first packet\n", __func__));
        }

        /*
         * Append group record.
         * If we have sources, we don't know how many yet.
         */
        mr.mr_type = type;
        mr.mr_datalen = 0;
        mr.mr_numsrc = 0;
        mr.mr_addr = inm->in6m_addr;
        in6_clearscope(&mr.mr_addr);
        if (!m_append(m, sizeof(struct mldv2_record), (void *)&mr)) {
                if (m != m0) {
                        m_freem(m);
                }
                MLD_PRINTF(("%s: m_append() failed.\n", __func__));
                return -ENOMEM;
        }
        nbytes += sizeof(struct mldv2_record);

        /*
         * Append as many sources as will fit in the first packet.
         * If we are appending to a new packet, the chain allocation
         * may potentially use clusters; use m_getptr() in this case.
         * If we are appending to an existing packet, we need to obtain
         * a pointer to the group record after m_append(), in case a new
         * mbuf was allocated.
         *
         * Only append sources which are in-mode at t1. If we are
         * transitioning to MCAST_UNDEFINED state on the group, and
         * use_block_allow is zero, do not include source entries.
         * Otherwise, we need to include this source in the report.
         *
         * Only report recorded sources in our filter set when responding
         * to a group-source query.
         */
        if (record_has_sources) {
                if (m == m0) {
                        md = m_last(m);
                        pmr = (struct mldv2_record *)(mtod(md, uint8_t *) +
                            md->m_len - nbytes);
                } else {
                        md = m_getptr(m, 0, &off);
                        pmr = (struct mldv2_record *)(mtod(md, uint8_t *) +
                            off);
                }
                msrcs = 0;
                RB_FOREACH_SAFE(ims, ip6_msource_tree, &inm->in6m_srcs,
                    nims) {
                        MLD_PRINTF(("%s: visit node %s\n", __func__,
                            ip6_sprintf(&ims->im6s_addr)));
                        now = im6s_get_mode(inm, ims, 1);
                        MLD_PRINTF(("%s: node is %d\n", __func__, now));
                        if ((now != mode) ||
                            (now == mode &&
                            (!use_block_allow && mode == MCAST_UNDEFINED))) {
                                MLD_PRINTF(("%s: skip node\n", __func__));
                                continue;
                        }
                        if (is_source_query && ims->im6s_stp == 0) {
                                MLD_PRINTF(("%s: skip unrecorded node\n",
                                    __func__));
                                continue;
                        }
                        MLD_PRINTF(("%s: append node\n", __func__));
                        if (!m_append(m, sizeof(struct in6_addr),
                            (void *)&ims->im6s_addr)) {
                                if (m != m0) {
                                        m_freem(m);
                                }
                                MLD_PRINTF(("%s: m_append() failed.\n",
                                    __func__));
                                return -ENOMEM;
                        }
                        nbytes += sizeof(struct in6_addr);
                        ++msrcs;
                        if (msrcs == m0srcs) {
                                break;
                        }
                }
                MLD_PRINTF(("%s: msrcs is %d this packet\n", __func__,
                    msrcs));
                pmr->mr_numsrc = htons(msrcs);
                nbytes += (msrcs * sizeof(struct in6_addr));
        }

        if (is_source_query && msrcs == 0) {
                MLD_PRINTF(("%s: no recorded sources to report\n", __func__));
                if (m != m0) {
                        m_freem(m);
                }
                return 0;
        }

        /*
         * We are good to go with first packet.
         */
        if (m != m0) {
                MLD_PRINTF(("%s: enqueueing first packet\n", __func__));
                m->m_pkthdr.vt_nrecs = 1;
                IF_ENQUEUE(ifq, m);
        } else {
                m->m_pkthdr.vt_nrecs++;
        }
        /*
         * No further work needed if no source list in packet(s).
         */
        if (!record_has_sources) {
                return nbytes;
        }

        /*
         * Whilst sources remain to be announced, we need to allocate
         * a new packet and fill out as many sources as will fit.
         * Always try for a cluster first.
         */
        while (nims != NULL) {
                if (IF_QFULL(ifq)) {
                        MLD_PRINTF(("%s: outbound queue full\n", __func__));
                        return -ENOMEM;
                }
                m = m_getcl(M_DONTWAIT, MT_DATA, M_PKTHDR);
                if (m == NULL) {
                        m = m_gethdr(M_DONTWAIT, MT_DATA);
                }
                if (m == NULL) {
                        return -ENOMEM;
                }
                mld_save_context(m, ifp);
                md = m_getptr(m, 0, &off);
                pmr = (struct mldv2_record *)(mtod(md, uint8_t *) + off);
                MLD_PRINTF(("%s: allocated next packet\n", __func__));

                if (!m_append(m, sizeof(struct mldv2_record), (void *)&mr)) {
                        if (m != m0) {
                                m_freem(m);
                        }
                        MLD_PRINTF(("%s: m_append() failed.\n", __func__));
                        return -ENOMEM;
                }
                m->m_pkthdr.vt_nrecs = 1;
                nbytes += sizeof(struct mldv2_record);

                m0srcs = (ifp->if_mtu - MLD_MTUSPACE -
                    sizeof(struct mldv2_record)) / sizeof(struct in6_addr);

                msrcs = 0;
                RB_FOREACH_FROM(ims, ip6_msource_tree, nims) {
                        MLD_PRINTF(("%s: visit node %s\n",
                            __func__, ip6_sprintf(&ims->im6s_addr)));
                        now = im6s_get_mode(inm, ims, 1);
                        if ((now != mode) ||
                            (now == mode &&
                            (!use_block_allow && mode == MCAST_UNDEFINED))) {
                                MLD_PRINTF(("%s: skip node\n", __func__));
                                continue;
                        }
                        if (is_source_query && ims->im6s_stp == 0) {
                                MLD_PRINTF(("%s: skip unrecorded node\n",
                                    __func__));
                                continue;
                        }
                        MLD_PRINTF(("%s: append node\n", __func__));
                        if (!m_append(m, sizeof(struct in6_addr),
                            (void *)&ims->im6s_addr)) {
                                if (m != m0) {
                                        m_freem(m);
                                }
                                MLD_PRINTF(("%s: m_append() failed.\n",
                                    __func__));
                                return -ENOMEM;
                        }
                        ++msrcs;
                        if (msrcs == m0srcs) {
                                break;
                        }
                }
                pmr->mr_numsrc = htons(msrcs);
                nbytes += (msrcs * sizeof(struct in6_addr));

                MLD_PRINTF(("%s: enqueueing next packet\n", __func__));
                IF_ENQUEUE(ifq, m);
        }

        return nbytes;
}

/*
 * Type used to mark record pass completion.
 * We exploit the fact we can cast to this easily from the
 * current filter modes on each ip_msource node.
 */
typedef enum {
        REC_NONE = 0x00,        /* MCAST_UNDEFINED */
        REC_ALLOW = 0x01,       /* MCAST_INCLUDE */
        REC_BLOCK = 0x02,       /* MCAST_EXCLUDE */
        REC_FULL = REC_ALLOW | REC_BLOCK
} rectype_t;

/*
 * Enqueue an MLDv2 filter list change to the given output queue.
 *
 * Source list filter state is held in an RB-tree. When the filter list
 * for a group is changed without changing its mode, we need to compute
 * the deltas between T0 and T1 for each source in the filter set,
 * and enqueue the appropriate ALLOW_NEW/BLOCK_OLD records.
 *
 * As we may potentially queue two record types, and the entire R-B tree
 * needs to be walked at once, we break this out into its own function
 * so we can generate a tightly packed queue of packets.
 *
 * XXX This could be written to only use one tree walk, although that makes
 * serializing into the mbuf chains a bit harder. For now we do two walks
 * which makes things easier on us, and it may or may not be harder on
 * the L2 cache.
 *
 * If successful the size of all data appended to the queue is returned,
 * otherwise an error code less than zero is returned, or zero if
 * no record(s) were appended.
 */
static int
mld_v2_enqueue_filter_change(struct ifqueue *ifq, struct in6_multi *inm)
{
        static const int MINRECLEN =
            sizeof(struct mldv2_record) + sizeof(struct in6_addr);
        struct ifnet            *ifp;
        struct mldv2_record      mr;
        struct mldv2_record     *pmr;
        struct ip6_msource      *ims, *nims;
        struct mbuf             *m, *m0, *md;
        int                      m0srcs, nbytes, npbytes, off, rsrcs, schanged;
        int                      nallow, nblock;
        uint8_t                  mode, now, then;
        rectype_t                crt, drt, nrt;

        IN6M_LOCK_ASSERT_HELD(inm);

        if (inm->in6m_nsrc == 0 ||
            (inm->in6m_st[0].iss_asm > 0 && inm->in6m_st[1].iss_asm > 0)) {
                return 0;
        }

        ifp = inm->in6m_ifp;                    /* interface */
        mode = inm->in6m_st[1].iss_fmode;       /* filter mode at t1 */
        crt = REC_NONE; /* current group record type */
        drt = REC_NONE; /* mask of completed group record types */
        nrt = REC_NONE; /* record type for current node */
        m0srcs = 0;     /* # source which will fit in current mbuf chain */
        npbytes = 0;    /* # of bytes appended this packet */
        nbytes = 0;     /* # of bytes appended to group's state-change queue */
        rsrcs = 0;      /* # sources encoded in current record */
        schanged = 0;   /* # nodes encoded in overall filter change */
        nallow = 0;     /* # of source entries in ALLOW_NEW */
        nblock = 0;     /* # of source entries in BLOCK_OLD */
        nims = NULL;    /* next tree node pointer */

        /*
         * For each possible filter record mode.
         * The first kind of source we encounter tells us which
         * is the first kind of record we start appending.
         * If a node transitioned to UNDEFINED at t1, its mode is treated
         * as the inverse of the group's filter mode.
         */
        while (drt != REC_FULL) {
                do {
                        m0 = ifq->ifq_tail;
                        if (m0 != NULL &&
                            (m0->m_pkthdr.vt_nrecs + 1 <=
                            MLD_V2_REPORT_MAXRECS) &&
                            (m0->m_pkthdr.len + MINRECLEN) <
                            (ifp->if_mtu - MLD_MTUSPACE)) {
                                m = m0;
                                m0srcs = (ifp->if_mtu - m0->m_pkthdr.len -
                                    sizeof(struct mldv2_record)) /
                                    sizeof(struct in6_addr);
                                MLD_PRINTF(("%s: use previous packet\n",
                                    __func__));
                        } else {
                                m = m_getcl(M_DONTWAIT, MT_DATA, M_PKTHDR);
                                if (m == NULL) {
                                        m = m_gethdr(M_DONTWAIT, MT_DATA);
                                }
                                if (m == NULL) {
                                        MLD_PRINTF(("%s: m_get*() failed\n",
                                            __func__));
                                        return -ENOMEM;
                                }
                                m->m_pkthdr.vt_nrecs = 0;
                                mld_save_context(m, ifp);
                                m0srcs = (ifp->if_mtu - MLD_MTUSPACE -
                                    sizeof(struct mldv2_record)) /
                                    sizeof(struct in6_addr);
                                npbytes = 0;
                                MLD_PRINTF(("%s: allocated new packet\n",
                                    __func__));
                        }
                        /*
                         * Append the MLD group record header to the
                         * current packet's data area.
                         * Recalculate pointer to free space for next
                         * group record, in case m_append() allocated
                         * a new mbuf or cluster.
                         */
                        memset(&mr, 0, sizeof(mr));
                        mr.mr_addr = inm->in6m_addr;
                        in6_clearscope(&mr.mr_addr);
                        if (!m_append(m, sizeof(mr), (void *)&mr)) {
                                if (m != m0) {
                                        m_freem(m);
                                }
                                MLD_PRINTF(("%s: m_append() failed\n",
                                    __func__));
                                return -ENOMEM;
                        }
                        npbytes += sizeof(struct mldv2_record);
                        if (m != m0) {
                                /* new packet; offset in chain */
                                md = m_getptr(m, npbytes -
                                    sizeof(struct mldv2_record), &off);
                                pmr = (struct mldv2_record *)(mtod(md,
                                    uint8_t *) + off);
                        } else {
                                /* current packet; offset from last append */
                                md = m_last(m);
                                pmr = (struct mldv2_record *)(mtod(md,
                                    uint8_t *) + md->m_len -
                                    sizeof(struct mldv2_record));
                        }
                        /*
                         * Begin walking the tree for this record type
                         * pass, or continue from where we left off
                         * previously if we had to allocate a new packet.
                         * Only report deltas in-mode at t1.
                         * We need not report included sources as allowed
                         * if we are in inclusive mode on the group,
                         * however the converse is not true.
                         */
                        rsrcs = 0;
                        if (nims == NULL) {
                                nims = RB_MIN(ip6_msource_tree,
                                    &inm->in6m_srcs);
                        }
                        RB_FOREACH_FROM(ims, ip6_msource_tree, nims) {
                                MLD_PRINTF(("%s: visit node %s\n", __func__,
                                    ip6_sprintf(&ims->im6s_addr)));
                                now = im6s_get_mode(inm, ims, 1);
                                then = im6s_get_mode(inm, ims, 0);
                                MLD_PRINTF(("%s: mode: t0 %d, t1 %d\n",
                                    __func__, then, now));
                                if (now == then) {
                                        MLD_PRINTF(("%s: skip unchanged\n",
                                            __func__));
                                        continue;
                                }
                                if (mode == MCAST_EXCLUDE &&
                                    now == MCAST_INCLUDE) {
                                        MLD_PRINTF(("%s: skip IN src on EX "
                                            "group\n", __func__));
                                        continue;
                                }
                                nrt = (rectype_t)now;
                                if (nrt == REC_NONE) {
                                        nrt = (rectype_t)(~mode & REC_FULL);
                                }
                                if (schanged++ == 0) {
                                        crt = nrt;
                                } else if (crt != nrt) {
                                        continue;
                                }
                                if (!m_append(m, sizeof(struct in6_addr),
                                    (void *)&ims->im6s_addr)) {
                                        if (m != m0) {
                                                m_freem(m);
                                        }
                                        MLD_PRINTF(("%s: m_append() failed\n",
                                            __func__));
                                        return -ENOMEM;
                                }
                                nallow += !!(crt == REC_ALLOW);
                                nblock += !!(crt == REC_BLOCK);
                                if (++rsrcs == m0srcs) {
                                        break;
                                }
                        }
                        /*
                         * If we did not append any tree nodes on this
                         * pass, back out of allocations.
                         */
                        if (rsrcs == 0) {
                                npbytes -= sizeof(struct mldv2_record);
                                if (m != m0) {
                                        MLD_PRINTF(("%s: m_free(m)\n",
                                            __func__));
                                        m_freem(m);
                                } else {
                                        MLD_PRINTF(("%s: m_adj(m, -mr)\n",
                                            __func__));
                                        m_adj(m, -((int)sizeof(
                                                    struct mldv2_record)));
                                }
                                continue;
                        }
                        npbytes += (rsrcs * sizeof(struct in6_addr));
                        if (crt == REC_ALLOW) {
                                pmr->mr_type = MLD_ALLOW_NEW_SOURCES;
                        } else if (crt == REC_BLOCK) {
                                pmr->mr_type = MLD_BLOCK_OLD_SOURCES;
                        }
                        pmr->mr_numsrc = htons(rsrcs);
                        /*
                         * Count the new group record, and enqueue this
                         * packet if it wasn't already queued.
                         */
                        m->m_pkthdr.vt_nrecs++;
                        if (m != m0) {
                                IF_ENQUEUE(ifq, m);
                        }
                        nbytes += npbytes;
                } while (nims != NULL);
                drt |= crt;
                crt = (~crt & REC_FULL);
        }

        MLD_PRINTF(("%s: queued %d ALLOW_NEW, %d BLOCK_OLD\n", __func__,
            nallow, nblock));

        return nbytes;
}

static int
mld_v2_merge_state_changes(struct in6_multi *inm, struct ifqueue *ifscq)
{
        struct ifqueue  *gq;
        struct mbuf     *m;             /* pending state-change */
        struct mbuf     *m0;            /* copy of pending state-change */
        struct mbuf     *mt;            /* last state-change in packet */
        struct mbuf     *n;
        int              docopy, domerge;
        u_int            recslen;

        IN6M_LOCK_ASSERT_HELD(inm);

        docopy = 0;
        domerge = 0;
        recslen = 0;

        /*
         * If there are further pending retransmissions, make a writable
         * copy of each queued state-change message before merging.
         */
        if (inm->in6m_scrv > 0) {
                docopy = 1;
        }

        gq = &inm->in6m_scq;
#ifdef MLD_DEBUG
        if (gq->ifq_head == NULL) {
                MLD_PRINTF(("%s: WARNING: queue for inm 0x%llx is empty\n",
                    __func__, (uint64_t)VM_KERNEL_ADDRPERM(inm)));
        }
#endif

        /*
         * Use IF_REMQUEUE() instead of IF_DEQUEUE() below, since the
         * packet might not always be at the head of the ifqueue.
         */
        m = gq->ifq_head;
        while (m != NULL) {
                /*
                 * Only merge the report into the current packet if
                 * there is sufficient space to do so; an MLDv2 report
                 * packet may only contain 65,535 group records.
                 * Always use a simple mbuf chain concatentation to do this,
                 * as large state changes for single groups may have
                 * allocated clusters.
                 */
                domerge = 0;
                mt = ifscq->ifq_tail;
                if (mt != NULL) {
                        recslen = m_length(m);

                        if ((mt->m_pkthdr.vt_nrecs +
                            m->m_pkthdr.vt_nrecs <=
                            MLD_V2_REPORT_MAXRECS) &&
                            (mt->m_pkthdr.len + recslen <=
                            (inm->in6m_ifp->if_mtu - MLD_MTUSPACE))) {
                                domerge = 1;
                        }
                }

                if (!domerge && IF_QFULL(gq)) {
                        MLD_PRINTF(("%s: outbound queue full, skipping whole "
                            "packet 0x%llx\n", __func__,
                            (uint64_t)VM_KERNEL_ADDRPERM(m)));
                        n = m->m_nextpkt;
                        if (!docopy) {
                                IF_REMQUEUE(gq, m);
                                m_freem(m);
                        }
                        m = n;
                        continue;
                }

                if (!docopy) {
                        MLD_PRINTF(("%s: dequeueing 0x%llx\n", __func__,
                            (uint64_t)VM_KERNEL_ADDRPERM(m)));
                        n = m->m_nextpkt;
                        IF_REMQUEUE(gq, m);
                        m0 = m;
                        m = n;
                } else {
                        MLD_PRINTF(("%s: copying 0x%llx\n", __func__,
                            (uint64_t)VM_KERNEL_ADDRPERM(m)));
                        m0 = m_dup(m, M_NOWAIT);
                        if (m0 == NULL) {
                                return ENOMEM;
                        }
                        m0->m_nextpkt = NULL;
                        m = m->m_nextpkt;
                }

                if (!domerge) {
                        MLD_PRINTF(("%s: queueing 0x%llx to ifscq 0x%llx)\n",
                            __func__, (uint64_t)VM_KERNEL_ADDRPERM(m0),
                            (uint64_t)VM_KERNEL_ADDRPERM(ifscq)));
                        IF_ENQUEUE(ifscq, m0);
                } else {
                        struct mbuf *mtl;       /* last mbuf of packet mt */

                        MLD_PRINTF(("%s: merging 0x%llx with ifscq tail "
                            "0x%llx)\n", __func__,
                            (uint64_t)VM_KERNEL_ADDRPERM(m0),
                            (uint64_t)VM_KERNEL_ADDRPERM(mt)));

                        mtl = m_last(mt);
                        m0->m_flags &= ~M_PKTHDR;
                        mt->m_pkthdr.len += recslen;
                        mt->m_pkthdr.vt_nrecs +=
                            m0->m_pkthdr.vt_nrecs;

                        mtl->m_next = m0;
                }
        }

        return 0;
}

/*
 * Respond to a pending MLDv2 General Query.
 */
static uint32_t
mld_v2_dispatch_general_query(struct mld_ifinfo *mli)
{
        struct ifnet            *ifp;
        struct in6_multi        *inm;
        struct in6_multistep    step;
        int                      retval;

        MLI_LOCK_ASSERT_HELD(mli);

        VERIFY(mli->mli_version == MLD_VERSION_2);

        ifp = mli->mli_ifp;
        MLI_UNLOCK(mli);

        in6_multihead_lock_shared();
        IN6_FIRST_MULTI(step, inm);
        while (inm != NULL) {
                IN6M_LOCK(inm);
                if (inm->in6m_ifp != ifp) {
                        goto next;
                }

                switch (inm->in6m_state) {
                case MLD_NOT_MEMBER:
                case MLD_SILENT_MEMBER:
                        break;
                case MLD_REPORTING_MEMBER:
                case MLD_IDLE_MEMBER:
                case MLD_LAZY_MEMBER:
                case MLD_SLEEPING_MEMBER:
                case MLD_AWAKENING_MEMBER:
                        inm->in6m_state = MLD_REPORTING_MEMBER;
                        MLI_LOCK(mli);
                        retval = mld_v2_enqueue_group_record(&mli->mli_gq,
                            inm, 0, 0, 0, 0);
                        MLI_UNLOCK(mli);
                        MLD_PRINTF(("%s: enqueue record = %d\n",
                            __func__, retval));
                        break;
                case MLD_G_QUERY_PENDING_MEMBER:
                case MLD_SG_QUERY_PENDING_MEMBER:
                case MLD_LEAVING_MEMBER:
                        break;
                }
next:
                IN6M_UNLOCK(inm);
                IN6_NEXT_MULTI(step, inm);
        }
        in6_multihead_lock_done();

        MLI_LOCK(mli);
        mld_dispatch_queue_locked(mli, &mli->mli_gq, MLD_MAX_RESPONSE_BURST);
        MLI_LOCK_ASSERT_HELD(mli);

        /*
         * Slew transmission of bursts over 1 second intervals.
         */
        if (mli->mli_gq.ifq_head != NULL) {
                mli->mli_v2_timer = 1 + MLD_RANDOM_DELAY(
                        MLD_RESPONSE_BURST_INTERVAL);
        }

        return mli->mli_v2_timer;
}

/*
 * Transmit the next pending message in the output queue.
 *
 * Must not be called with in6m_lockm or mli_lock held.
 */
static void
mld_dispatch_packet(struct mbuf *m)
{
        struct ip6_moptions     *im6o;
        struct ifnet            *ifp;
        struct ifnet            *oifp = NULL;
        struct mbuf             *m0;
        struct mbuf             *md;
        struct ip6_hdr          *ip6;
        struct mld_hdr          *mld;
        int                      error;
        int                      off;
        int                      type;

        MLD_PRINTF(("%s: transmit 0x%llx\n", __func__,
            (uint64_t)VM_KERNEL_ADDRPERM(m)));

        /*
         * Check if the ifnet is still attached.
         */
        ifp = mld_restore_context(m);
        if (ifp == NULL || !ifnet_is_attached(ifp, 0)) {
                MLD_PRINTF(("%s: dropped 0x%llx as ifindex %u went away.\n",
                    __func__, (uint64_t)VM_KERNEL_ADDRPERM(m),
                    (u_int)if_index));
                m_freem(m);
                ip6stat.ip6s_noroute++;
                return;
        }

        im6o = ip6_allocmoptions(M_WAITOK);
        if (im6o == NULL) {
                m_freem(m);
                return;
        }

        im6o->im6o_multicast_hlim  = 1;
        im6o->im6o_multicast_loop = 0;
        im6o->im6o_multicast_ifp = ifp;

        if (m->m_flags & M_MLDV1) {
                m0 = m;
        } else {
                m0 = mld_v2_encap_report(ifp, m);
                if (m0 == NULL) {
                        MLD_PRINTF(("%s: dropped 0x%llx\n", __func__,
                            (uint64_t)VM_KERNEL_ADDRPERM(m)));
                        /*
                         * mld_v2_encap_report() has already freed our mbuf.
                         */
                        IM6O_REMREF(im6o);
                        ip6stat.ip6s_odropped++;
                        return;
                }
        }

        mld_scrub_context(m0);
        m->m_flags &= ~(M_PROTOFLAGS);
        m0->m_pkthdr.rcvif = lo_ifp;

        ip6 = mtod(m0, struct ip6_hdr *);
        (void)in6_setscope(&ip6->ip6_dst, ifp, NULL);

        /*
         * Retrieve the ICMPv6 type before handoff to ip6_output(),
         * so we can bump the stats.
         */
        md = m_getptr(m0, sizeof(struct ip6_hdr), &off);
        mld = (struct mld_hdr *)(mtod(md, uint8_t *) + off);
        type = mld->mld_type;

        if (ifp->if_eflags & IFEF_TXSTART) {
                /*
                 * Use control service class if the outgoing
                 * interface supports transmit-start model.
                 */
                (void) m_set_service_class(m0, MBUF_SC_CTL);
        }

        error = ip6_output(m0, &mld_po, NULL, IPV6_UNSPECSRC, im6o,
            &oifp, NULL);

        IM6O_REMREF(im6o);

        if (error) {
                MLD_PRINTF(("%s: ip6_output(0x%llx) = %d\n", __func__,
                    (uint64_t)VM_KERNEL_ADDRPERM(m0), error));
                if (oifp != NULL) {
                        ifnet_release(oifp);
                }
                return;
        }

        icmp6stat.icp6s_outhist[type]++;
        if (oifp != NULL) {
                icmp6_ifstat_inc(oifp, ifs6_out_msg);
                switch (type) {
                case MLD_LISTENER_REPORT:
                case MLDV2_LISTENER_REPORT:
                        icmp6_ifstat_inc(oifp, ifs6_out_mldreport);
                        break;
                case MLD_LISTENER_DONE:
                        icmp6_ifstat_inc(oifp, ifs6_out_mlddone);
                        break;
                }
                ifnet_release(oifp);
        }
}

/*
 * Encapsulate an MLDv2 report.
 *
 * KAME IPv6 requires that hop-by-hop options be passed separately,
 * and that the IPv6 header be prepended in a separate mbuf.
 *
 * Returns a pointer to the new mbuf chain head, or NULL if the
 * allocation failed.
 */
static struct mbuf *
mld_v2_encap_report(struct ifnet *ifp, struct mbuf *m)
{
        struct mbuf             *mh;
        struct mldv2_report     *mld;
        struct ip6_hdr          *ip6;
        struct in6_ifaddr       *ia;
        int                      mldreclen;

        VERIFY(m->m_flags & M_PKTHDR);

        /*
         * RFC3590: OK to send as :: or tentative during DAD.
         */
        ia = in6ifa_ifpforlinklocal(ifp, IN6_IFF_NOTREADY | IN6_IFF_ANYCAST);
        if (ia == NULL) {
                MLD_PRINTF(("%s: warning: ia is NULL\n", __func__));
        }

        MGETHDR(mh, M_DONTWAIT, MT_HEADER);
        if (mh == NULL) {
                if (ia != NULL) {
                        IFA_REMREF(&ia->ia_ifa);
                }
                m_freem(m);
                return NULL;
        }
        MH_ALIGN(mh, sizeof(struct ip6_hdr) + sizeof(struct mldv2_report));

        mldreclen = m_length(m);
        MLD_PRINTF(("%s: mldreclen is %d\n", __func__, mldreclen));

        mh->m_len = sizeof(struct ip6_hdr) + sizeof(struct mldv2_report);
        mh->m_pkthdr.len = sizeof(struct ip6_hdr) +
            sizeof(struct mldv2_report) + mldreclen;

        ip6 = mtod(mh, struct ip6_hdr *);
        ip6->ip6_flow = 0;
        ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
        ip6->ip6_vfc |= IPV6_VERSION;
        ip6->ip6_nxt = IPPROTO_ICMPV6;
        if (ia != NULL) {
                IFA_LOCK(&ia->ia_ifa);
        }
        ip6->ip6_src = ia ? ia->ia_addr.sin6_addr : in6addr_any;
        if (ia != NULL) {
                IFA_UNLOCK(&ia->ia_ifa);
                IFA_REMREF(&ia->ia_ifa);
                ia = NULL;
        }
        ip6->ip6_dst = in6addr_linklocal_allv2routers;
        /* scope ID will be set in netisr */

        mld = (struct mldv2_report *)(ip6 + 1);
        mld->mld_type = MLDV2_LISTENER_REPORT;
        mld->mld_code = 0;
        mld->mld_cksum = 0;
        mld->mld_v2_reserved = 0;
        mld->mld_v2_numrecs = htons(m->m_pkthdr.vt_nrecs);
        m->m_pkthdr.vt_nrecs = 0;
        m->m_flags &= ~M_PKTHDR;

        mh->m_next = m;
        mld->mld_cksum = in6_cksum(mh, IPPROTO_ICMPV6,
            sizeof(struct ip6_hdr), sizeof(struct mldv2_report) + mldreclen);
        return mh;
}

#ifdef MLD_DEBUG
static const char *
mld_rec_type_to_str(const int type)
{
        switch (type) {
        case MLD_CHANGE_TO_EXCLUDE_MODE:
                return "TO_EX";
        case MLD_CHANGE_TO_INCLUDE_MODE:
                return "TO_IN";
        case MLD_MODE_IS_EXCLUDE:
                return "MODE_EX";
        case MLD_MODE_IS_INCLUDE:
                return "MODE_IN";
        case MLD_ALLOW_NEW_SOURCES:
                return "ALLOW_NEW";
        case MLD_BLOCK_OLD_SOURCES:
                return "BLOCK_OLD";
        default:
                break;
        }
        return "unknown";
}
#endif

void
mld_init(void)
{
        MLD_PRINTF(("%s: initializing\n", __func__));

        /* Setup lock group and attribute for mld_mtx */
        mld_mtx_grp_attr = lck_grp_attr_alloc_init();
        mld_mtx_grp = lck_grp_alloc_init("mld_mtx\n", mld_mtx_grp_attr);
        mld_mtx_attr = lck_attr_alloc_init();
        lck_mtx_init(&mld_mtx, mld_mtx_grp, mld_mtx_attr);

        ip6_initpktopts(&mld_po);
        mld_po.ip6po_hlim = 1;
        mld_po.ip6po_hbh = &mld_ra.hbh;
        mld_po.ip6po_prefer_tempaddr = IP6PO_TEMPADDR_NOTPREFER;
        mld_po.ip6po_flags = IP6PO_DONTFRAG;
        LIST_INIT(&mli_head);

        mli_size = sizeof(struct mld_ifinfo);
        mli_zone = zinit(mli_size, MLI_ZONE_MAX * mli_size,
            0, MLI_ZONE_NAME);
        if (mli_zone == NULL) {
                panic("%s: failed allocating %s", __func__, MLI_ZONE_NAME);
                /* NOTREACHED */
        }
        zone_change(mli_zone, Z_EXPAND, TRUE);
        zone_change(mli_zone, Z_CALLERACCT, FALSE);
}