/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2003 IPNET Internet Communication Company
 * Copyright (c) 2011 - 2012 Rozhuk Ivan <rozhuk.im@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * Author: Ruslan Ermilov <ru@FreeBSD.org>
 */

#include <sys/param.h>
#include <sys/errno.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/queue.h>
#include <sys/socket.h>
#include <sys/systm.h>

#include <net/ethernet.h>
#include <net/if.h>
#include <net/if_vlan_var.h>

#include <netgraph/ng_message.h>
#include <netgraph/ng_parse.h>
#include <netgraph/ng_vlan.h>
#include <netgraph/netgraph.h>

struct ng_vlan_private {
        hook_p          downstream_hook;
        hook_p          nomatch_hook;
        uint32_t        decap_enable;
        uint32_t        encap_enable;
        uint16_t        encap_proto;
        hook_p          vlan_hook[(EVL_VLID_MASK + 1)];
};
typedef struct ng_vlan_private *priv_p;

#define ETHER_VLAN_HDR_LEN (ETHER_HDR_LEN + ETHER_VLAN_ENCAP_LEN)
#define VLAN_TAG_MASK   0xFFFF
#define HOOK_VLAN_TAG_SET_MASK ((uintptr_t)((~0) & ~(VLAN_TAG_MASK)))
#define IS_HOOK_VLAN_SET(hdata) \
            ((((uintptr_t)hdata) & HOOK_VLAN_TAG_SET_MASK) == HOOK_VLAN_TAG_SET_MASK)

static ng_constructor_t ng_vlan_constructor;
static ng_rcvmsg_t      ng_vlan_rcvmsg;
static ng_shutdown_t    ng_vlan_shutdown;
static ng_newhook_t     ng_vlan_newhook;
static ng_rcvdata_t     ng_vlan_rcvdata;
static ng_disconnect_t  ng_vlan_disconnect;

/* Parse type for struct ng_vlan_filter. */
static const struct ng_parse_struct_field ng_vlan_filter_fields[] =
        NG_VLAN_FILTER_FIELDS;
static const struct ng_parse_type ng_vlan_filter_type = {
        &ng_parse_struct_type,
        &ng_vlan_filter_fields
};

static int
ng_vlan_getTableLength(const struct ng_parse_type *type,
    const u_char *start, const u_char *buf)
{
        const struct ng_vlan_table *const table =
            (const struct ng_vlan_table *)(buf - sizeof(u_int32_t));

        return table->n;
}

/* Parse type for struct ng_vlan_table. */
static const struct ng_parse_array_info ng_vlan_table_array_info = {
        &ng_vlan_filter_type,
        ng_vlan_getTableLength
};
static const struct ng_parse_type ng_vlan_table_array_type = {
        &ng_parse_array_type,
        &ng_vlan_table_array_info
};
static const struct ng_parse_struct_field ng_vlan_table_fields[] =
        NG_VLAN_TABLE_FIELDS;
static const struct ng_parse_type ng_vlan_table_type = {
        &ng_parse_struct_type,
        &ng_vlan_table_fields
};

/* List of commands and how to convert arguments to/from ASCII. */
static const struct ng_cmdlist ng_vlan_cmdlist[] = {
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_ADD_FILTER,
          "addfilter",
          &ng_vlan_filter_type,
          NULL
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_DEL_FILTER,
          "delfilter",
          &ng_parse_hookbuf_type,
          NULL
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_GET_TABLE,
          "gettable",
          NULL,
          &ng_vlan_table_type
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_DEL_VID_FLT,
          "delvidflt",
          &ng_parse_uint16_type,
          NULL
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_GET_DECAP,
          "getdecap",
          NULL,
          &ng_parse_hint32_type
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_SET_DECAP,
          "setdecap",
          &ng_parse_hint32_type,
          NULL
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_GET_ENCAP,
          "getencap",
          NULL,
          &ng_parse_hint32_type
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_SET_ENCAP,
          "setencap",
          &ng_parse_hint32_type,
          NULL
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_GET_ENCAP_PROTO,
          "getencapproto",
          NULL,
          &ng_parse_hint16_type
        },
        {
          NGM_VLAN_COOKIE,
          NGM_VLAN_SET_ENCAP_PROTO,
          "setencapproto",
          &ng_parse_hint16_type,
          NULL
        },
        { 0 }
};

static struct ng_type ng_vlan_typestruct = {
        .version =      NG_ABI_VERSION,
        .name =         NG_VLAN_NODE_TYPE,
        .constructor =  ng_vlan_constructor,
        .rcvmsg =       ng_vlan_rcvmsg,
        .shutdown =     ng_vlan_shutdown,
        .newhook =      ng_vlan_newhook,
        .rcvdata =      ng_vlan_rcvdata,
        .disconnect =   ng_vlan_disconnect,
        .cmdlist =      ng_vlan_cmdlist,
};
NETGRAPH_INIT(vlan, &ng_vlan_typestruct);

/*
 * Helper functions.
 */

static __inline int
m_chk(struct mbuf **mp, int len)
{

        if ((*mp)->m_pkthdr.len < len) {
                m_freem((*mp));
                (*mp) = NULL;
                return (EINVAL);
        }
        if ((*mp)->m_len < len && ((*mp) = m_pullup((*mp), len)) == NULL)
                return (ENOBUFS);

        return (0);
}

/*
 * Netgraph node functions.
 */

static int
ng_vlan_constructor(node_p node)
{
        priv_p priv;

        priv = malloc(sizeof(*priv), M_NETGRAPH, M_WAITOK | M_ZERO);
        priv->decap_enable = 0;
        priv->encap_enable = VLAN_ENCAP_FROM_FILTER;
        priv->encap_proto = htons(ETHERTYPE_VLAN);
        NG_NODE_SET_PRIVATE(node, priv);
        return (0);
}

static int
ng_vlan_newhook(node_p node, hook_p hook, const char *name)
{
        const priv_p priv = NG_NODE_PRIVATE(node);

        if (strcmp(name, NG_VLAN_HOOK_DOWNSTREAM) == 0)
                priv->downstream_hook = hook;
        else if (strcmp(name, NG_VLAN_HOOK_NOMATCH) == 0)
                priv->nomatch_hook = hook;
        else {
                /*
                 * Any other hook name is valid and can
                 * later be associated with a filter rule.
                 */
        }
        NG_HOOK_SET_PRIVATE(hook, NULL);
        return (0);
}

static int
ng_vlan_rcvmsg(node_p node, item_p item, hook_p lasthook)
{
        const priv_p priv = NG_NODE_PRIVATE(node);
        struct ng_mesg *msg, *resp = NULL;
        struct ng_vlan_filter *vf;
        hook_p hook;
        struct ng_vlan_table *t;
        uintptr_t hook_data;
        int i, vlan_count;
        uint16_t vid;
        int error = 0;

        NGI_GET_MSG(item, msg);
        /* Deal with message according to cookie and command. */
        switch (msg->header.typecookie) {
        case NGM_VLAN_COOKIE:
                switch (msg->header.cmd) {
                case NGM_VLAN_ADD_FILTER:
                        /* Check that message is long enough. */
                        if (msg->header.arglen != sizeof(*vf)) {
                                error = EINVAL;
                                break;
                        }
                        vf = (struct ng_vlan_filter *)msg->data;
                        /* Sanity check the VLAN ID value. */
#ifdef  NG_VLAN_USE_OLD_VLAN_NAME
                        if (vf->vid == 0 && vf->vid != vf->vlan) {
                                vf->vid = vf->vlan;
                        } else if (vf->vid != 0 && vf->vlan != 0 &&
                            vf->vid != vf->vlan) {
                                error = EINVAL;
                                break;
                        }
#endif
                        if (vf->vid & ~EVL_VLID_MASK ||
                            vf->pcp & ~7 ||
                            vf->cfi & ~1) {
                                error = EINVAL;
                                break;
                        }
                        /* Check that a referenced hook exists. */
                        hook = ng_findhook(node, vf->hook_name);
                        if (hook == NULL) {
                                error = ENOENT;
                                break;
                        }
                        /* And is not one of the special hooks. */
                        if (hook == priv->downstream_hook ||
                            hook == priv->nomatch_hook) {
                                error = EINVAL;
                                break;
                        }
                        /* And is not already in service. */
                        if (IS_HOOK_VLAN_SET(NG_HOOK_PRIVATE(hook))) {
                                error = EEXIST;
                                break;
                        }
                        /* Check we don't already trap this VLAN. */
                        if (priv->vlan_hook[vf->vid] != NULL) {
                                error = EEXIST;
                                break;
                        }
                        /* Link vlan and hook together. */
                        NG_HOOK_SET_PRIVATE(hook,
                            (void *)(HOOK_VLAN_TAG_SET_MASK |
                            EVL_MAKETAG(vf->vid, vf->pcp, vf->cfi)));
                        priv->vlan_hook[vf->vid] = hook;
                        break;
                case NGM_VLAN_DEL_FILTER:
                        /* Check that message is long enough. */
                        if (msg->header.arglen != NG_HOOKSIZ) {
                                error = EINVAL;
                                break;
                        }
                        /* Check that hook exists and is active. */
                        hook = ng_findhook(node, (char *)msg->data);
                        if (hook == NULL) {
                                error = ENOENT;
                                break;
                        }
                        hook_data = (uintptr_t)NG_HOOK_PRIVATE(hook);
                        if (IS_HOOK_VLAN_SET(hook_data) == 0) {
                                error = ENOENT;
                                break;
                        }

                        KASSERT(priv->vlan_hook[EVL_VLANOFTAG(hook_data)] == hook,
                            ("%s: NGM_VLAN_DEL_FILTER: Invalid VID for Hook = %s\n",
                            __func__, (char *)msg->data));

                        /* Purge a rule that refers to this hook. */
                        priv->vlan_hook[EVL_VLANOFTAG(hook_data)] = NULL;
                        NG_HOOK_SET_PRIVATE(hook, NULL);
                        break;
                case NGM_VLAN_DEL_VID_FLT:
                        /* Check that message is long enough. */
                        if (msg->header.arglen != sizeof(uint16_t)) {
                                error = EINVAL;
                                break;
                        }
                        vid = (*((uint16_t *)msg->data));
                        /* Sanity check the VLAN ID value. */
                        if (vid & ~EVL_VLID_MASK) {
                                error = EINVAL;
                                break;
                        }
                        /* Check that hook exists and is active. */
                        hook = priv->vlan_hook[vid];
                        if (hook == NULL) {
                                error = ENOENT;
                                break;
                        }
                        hook_data = (uintptr_t)NG_HOOK_PRIVATE(hook);
                        if (IS_HOOK_VLAN_SET(hook_data) == 0) {
                                error = ENOENT;
                                break;
                        }

                        KASSERT(EVL_VLANOFTAG(hook_data) == vid,
                            ("%s: NGM_VLAN_DEL_VID_FLT:"
                            " Invalid VID Hook = %us, must be: %us\n",
                            __func__, (uint16_t )EVL_VLANOFTAG(hook_data),
                            vid));

                        /* Purge a rule that refers to this hook. */
                        priv->vlan_hook[vid] = NULL;
                        NG_HOOK_SET_PRIVATE(hook, NULL);
                        break;
                case NGM_VLAN_GET_TABLE:
                        /* Calculate vlans. */
                        vlan_count = 0;
                        for (i = 0; i < (EVL_VLID_MASK + 1); i ++) {
                                if (priv->vlan_hook[i] != NULL &&
                                    NG_HOOK_IS_VALID(priv->vlan_hook[i]))
                                        vlan_count ++;
                        }

                        /* Allocate memory for response. */
                        NG_MKRESPONSE(resp, msg, sizeof(*t) +
                            vlan_count * sizeof(*t->filter), M_NOWAIT);
                        if (resp == NULL) {
                                error = ENOMEM;
                                break;
                        }

                        /* Pack data to response. */
                        t = (struct ng_vlan_table *)resp->data;
                        t->n = 0;
                        vf = &t->filter[0];
                        for (i = 0; i < (EVL_VLID_MASK + 1); i ++) {
                                hook = priv->vlan_hook[i];
                                if (hook == NULL || NG_HOOK_NOT_VALID(hook))
                                        continue;
                                hook_data = (uintptr_t)NG_HOOK_PRIVATE(hook);
                                if (IS_HOOK_VLAN_SET(hook_data) == 0)
                                        continue;

                                KASSERT(EVL_VLANOFTAG(hook_data) == i,
                                    ("%s: NGM_VLAN_GET_TABLE:"
                                    " hook %s VID = %us, must be: %i\n",
                                    __func__, NG_HOOK_NAME(hook),
                                    (uint16_t)EVL_VLANOFTAG(hook_data), i));

#ifdef  NG_VLAN_USE_OLD_VLAN_NAME
                                vf->vlan = i;
#endif
                                vf->vid = i;
                                vf->pcp = EVL_PRIOFTAG(hook_data);
                                vf->cfi = EVL_CFIOFTAG(hook_data);
                                strncpy(vf->hook_name,
                                    NG_HOOK_NAME(hook), NG_HOOKSIZ);
                                vf ++;
                                t->n ++;
                        }
                        break;
                case NGM_VLAN_GET_DECAP:
                        NG_MKRESPONSE(resp, msg, sizeof(uint32_t), M_NOWAIT);
                        if (resp == NULL) {
                                error = ENOMEM;
                                break;
                        }
                        (*((uint32_t *)resp->data)) = priv->decap_enable;
                        break;
                case NGM_VLAN_SET_DECAP:
                        if (msg->header.arglen != sizeof(uint32_t)) {
                                error = EINVAL;
                                break;
                        }
                        priv->decap_enable = (*((uint32_t *)msg->data));
                        break;
                case NGM_VLAN_GET_ENCAP:
                        NG_MKRESPONSE(resp, msg, sizeof(uint32_t), M_NOWAIT);
                        if (resp == NULL) {
                                error = ENOMEM;
                                break;
                        }
                        (*((uint32_t *)resp->data)) = priv->encap_enable;
                        break;
                case NGM_VLAN_SET_ENCAP:
                        if (msg->header.arglen != sizeof(uint32_t)) {
                                error = EINVAL;
                                break;
                        }
                        priv->encap_enable = (*((uint32_t *)msg->data));
                        break;
                case NGM_VLAN_GET_ENCAP_PROTO:
                        NG_MKRESPONSE(resp, msg, sizeof(uint16_t), M_NOWAIT);
                        if (resp == NULL) {
                                error = ENOMEM;
                                break;
                        }
                        (*((uint16_t *)resp->data)) = ntohs(priv->encap_proto);
                        break;
                case NGM_VLAN_SET_ENCAP_PROTO:
                        if (msg->header.arglen != sizeof(uint16_t)) {
                                error = EINVAL;
                                break;
                        }
                        priv->encap_proto = htons((*((uint16_t *)msg->data)));
                        break;
                default: /* Unknown command. */
                        error = EINVAL;
                        break;
                }
                break;
        case NGM_FLOW_COOKIE:
            {
                struct ng_mesg *copy;

                /*
                 * Flow control messages should come only
                 * from downstream.
                 */

                if (lasthook == NULL)
                        break;
                if (lasthook != priv->downstream_hook)
                        break;
                /* Broadcast the event to all uplinks. */
                for (i = 0; i < (EVL_VLID_MASK + 1); i ++) {
                        if (priv->vlan_hook[i] == NULL)
                                continue;

                        NG_COPYMESSAGE(copy, msg, M_NOWAIT);
                        if (copy == NULL)
                                continue;
                        NG_SEND_MSG_HOOK(error, node, copy,
                            priv->vlan_hook[i], 0);
                }
                break;
            }
        default: /* Unknown type cookie. */
                error = EINVAL;
                break;
        }
        NG_RESPOND_MSG(error, node, item, resp);
        NG_FREE_MSG(msg);
        return (error);
}

static int
ng_vlan_rcvdata(hook_p hook, item_p item)
{
        const priv_p priv = NG_NODE_PRIVATE(NG_HOOK_NODE(hook));
        struct ether_header *eh;
        struct ether_vlan_header *evl;
        int error;
        uintptr_t hook_data;
        uint16_t vid, eth_vtag;
        struct mbuf *m;
        hook_p dst_hook;

        NGI_GET_M(item, m);

        /* Make sure we have an entire header. */
        error = m_chk(&m, ETHER_HDR_LEN);
        if (error != 0)
                goto mchk_err;

        eh = mtod(m, struct ether_header *);
        if (hook == priv->downstream_hook) {
                /*
                 * If from downstream, select between a match hook
                 * or the nomatch hook.
                 */

                dst_hook = priv->nomatch_hook;

                /* Skip packets without tag. */
                if ((m->m_flags & M_VLANTAG) == 0 &&
                    eh->ether_type != priv->encap_proto) {
                        if (dst_hook == NULL)
                                goto net_down;
                        goto send_packet;
                }

                /* Process packets with tag. */
                if (m->m_flags & M_VLANTAG) {
                        /*
                         * Packet is tagged, m contains a normal
                         * Ethernet frame; tag is stored out-of-band.
                         */
                        evl = NULL;
                        vid = EVL_VLANOFTAG(m->m_pkthdr.ether_vtag);
                } else { /* eh->ether_type == priv->encap_proto */
                        error = m_chk(&m, ETHER_VLAN_HDR_LEN);
                        if (error != 0)
                                goto mchk_err;
                        evl = mtod(m, struct ether_vlan_header *);
                        vid = EVL_VLANOFTAG(ntohs(evl->evl_tag));
                }

                if (priv->vlan_hook[vid] != NULL) {
                        /*
                         * VLAN filter: always remove vlan tags and
                         * decapsulate packet.
                         */
                        dst_hook = priv->vlan_hook[vid];
                        if (evl == NULL) { /* m->m_flags & M_VLANTAG */
                                m->m_pkthdr.ether_vtag = 0;
                                m->m_flags &= ~M_VLANTAG;
                                goto send_packet;
                        }
                } else { /* nomatch_hook */
                        if (dst_hook == NULL)
                                goto net_down;
                        if (evl == NULL || priv->decap_enable == 0)
                                goto send_packet;
                        /* Save tag out-of-band. */
                        m->m_pkthdr.ether_vtag = ntohs(evl->evl_tag);
                        m->m_flags |= M_VLANTAG;
                }

                /*
                 * Decapsulate:
                 * TPID = ether type encap
                 * Move DstMAC and SrcMAC to ETHER_TYPE.
                 * Before:
                 *  [dmac] [smac] [TPID] [PCP/CFI/VID] [ether_type] [payload]
                 *  |-----------| >>>>>>>>>>>>>>>>>>>> |--------------------|
                 * After:
                 *  [free space ] [dmac] [smac] [ether_type] [payload]
                 *                |-----------| |--------------------|
                 */
                bcopy((char *)evl, ((char *)evl + ETHER_VLAN_ENCAP_LEN),
                    (ETHER_ADDR_LEN * 2));
                m_adj(m, ETHER_VLAN_ENCAP_LEN);
        } else {
                /*
                 * It is heading towards the downstream.
                 * If from nomatch, pass it unmodified.
                 * Otherwise, do the VLAN encapsulation.
                 */
                dst_hook = priv->downstream_hook;
                if (dst_hook == NULL)
                        goto net_down;
                if (hook != priv->nomatch_hook) {/* Filter hook. */
                        hook_data = (uintptr_t)NG_HOOK_PRIVATE(hook);
                        if (IS_HOOK_VLAN_SET(hook_data) == 0) {
                                /*
                                 * Packet from hook not in filter
                                 * call addfilter for this hook to fix.
                                 */
                                error = EOPNOTSUPP;
                                goto drop;
                        }
                        eth_vtag = (hook_data & VLAN_TAG_MASK);
                        if ((priv->encap_enable & VLAN_ENCAP_FROM_FILTER) == 0) {
                                /* Just set packet header tag and send. */
                                m->m_flags |= M_VLANTAG;
                                m->m_pkthdr.ether_vtag = eth_vtag;
                                goto send_packet;
                        }
                } else { /* nomatch_hook */
                        if ((priv->encap_enable & VLAN_ENCAP_FROM_NOMATCH) == 0 ||
                            (m->m_flags & M_VLANTAG) == 0)
                                goto send_packet;
                        /* Encapsulate tagged packet. */
                        eth_vtag = m->m_pkthdr.ether_vtag;
                        m->m_pkthdr.ether_vtag = 0;
                        m->m_flags &= ~M_VLANTAG;
                }

                /*
                 * Transform the Ethernet header into an Ethernet header
                 * with 802.1Q encapsulation.
                 * Mod of: ether_vlanencap.
                 *
                 * TPID = ether type encap
                 * Move DstMAC and SrcMAC from ETHER_TYPE.
                 * Before:
                 *  [free space ] [dmac] [smac] [ether_type] [payload]
                 *  <<<<<<<<<<<<< |-----------| |--------------------|
                 * After:
                 *  [dmac] [smac] [TPID] [PCP/CFI/VID] [ether_type] [payload]
                 *  |-----------| |-- inserted tag --| |--------------------|
                 */
                M_PREPEND(m, ETHER_VLAN_ENCAP_LEN, M_NOWAIT);
                if (m == NULL)
                        error = ENOMEM;
                else
                        error = m_chk(&m, ETHER_VLAN_HDR_LEN);
                if (error != 0)
                        goto mchk_err;

                evl = mtod(m, struct ether_vlan_header *);
                bcopy(((char *)evl + ETHER_VLAN_ENCAP_LEN),
                    (char *)evl, (ETHER_ADDR_LEN * 2));
                evl->evl_encap_proto = priv->encap_proto;
                evl->evl_tag = htons(eth_vtag);
        }

send_packet:
        NG_FWD_NEW_DATA(error, item, dst_hook, m);
        return (error);
net_down:
        error = ENETDOWN;
drop:
        m_freem(m);
mchk_err:
        NG_FREE_ITEM(item);
        return (error);
}

static int
ng_vlan_shutdown(node_p node)
{
        const priv_p priv = NG_NODE_PRIVATE(node);

        NG_NODE_SET_PRIVATE(node, NULL);
        NG_NODE_UNREF(node);
        free(priv, M_NETGRAPH);
        return (0);
}

static int
ng_vlan_disconnect(hook_p hook)
{
        const priv_p priv = NG_NODE_PRIVATE(NG_HOOK_NODE(hook));
        uintptr_t hook_data;

        if (hook == priv->downstream_hook)
                priv->downstream_hook = NULL;
        else if (hook == priv->nomatch_hook)
                priv->nomatch_hook = NULL;
        else {
                /* Purge a rule that refers to this hook. */
                hook_data = (uintptr_t)NG_HOOK_PRIVATE(hook);
                if (IS_HOOK_VLAN_SET(hook_data))
                        priv->vlan_hook[EVL_VLANOFTAG(hook_data)] = NULL;
        }
        NG_HOOK_SET_PRIVATE(hook, NULL);
        if ((NG_NODE_NUMHOOKS(NG_HOOK_NODE(hook)) == 0) &&
            (NG_NODE_IS_VALID(NG_HOOK_NODE(hook))))
                ng_rmnode_self(NG_HOOK_NODE(hook));
        return (0);
}