bin/named/lwresd.c

/*
 * Copyright (C) 2000-2009, 2012-2016  Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/* $Id: lwresd.c,v 1.60 2009/09/02 23:48:01 tbox Exp $ */

/*! \file
 * \brief
 * Main program for the Lightweight Resolver Daemon.
 *
 * To paraphrase the old saying about X11, "It's not a lightweight deamon
 * for resolvers, it's a deamon for lightweight resolvers".
 */

#include <config.h>

#include <stdlib.h>
#include <string.h>

#include <isc/list.h>
#include <isc/magic.h>
#include <isc/mem.h>
#include <isc/once.h>
#include <isc/print.h>
#include <isc/socket.h>
#include <isc/task.h>
#include <isc/util.h>

#include <isccfg/namedconf.h>

#include <dns/log.h>
#include <dns/result.h>
#include <dns/view.h>

#include <named/config.h>
#include <named/globals.h>
#include <named/log.h>
#include <named/lwaddr.h>
#include <named/lwresd.h>
#include <named/lwdclient.h>
#include <named/lwsearch.h>
#include <named/server.h>

#define LWRESD_MAGIC        ISC_MAGIC('L', 'W', 'R', 'D')
#define VALID_LWRESD(l)     ISC_MAGIC_VALID(l, LWRESD_MAGIC)

#define LWRESLISTENER_MAGIC ISC_MAGIC('L', 'W', 'R', 'L')
#define VALID_LWRESLISTENER(l)  ISC_MAGIC_VALID(l, LWRESLISTENER_MAGIC)

#define LWRESD_NCLIENTS_MAX     32768   /*%< max clients per task */

typedef ISC_LIST(ns_lwreslistener_t) ns_lwreslistenerlist_t;

static ns_lwreslistenerlist_t listeners;
static isc_mutex_t listeners_lock;
static isc_once_t once = ISC_ONCE_INIT;


static void
initialize_mutex(void) {
    RUNTIME_CHECK(isc_mutex_init(&listeners_lock) == ISC_R_SUCCESS);
}


/*%
 * Wrappers around our memory management stuff, for the lwres functions.
 */
void *
ns__lwresd_memalloc(void *arg, size_t size) {
    return (isc_mem_get(arg, size));
}

void
ns__lwresd_memfree(void *arg, void *mem, size_t size) {
    isc_mem_put(arg, mem, size);
}


#define CHECK(op)                       \
    do { result = (op);                 \
        if (result != ISC_R_SUCCESS) goto cleanup;  \
    } while (0)

static isc_result_t
buffer_putstr(isc_buffer_t *b, const char *s) {
    unsigned int len = strlen(s);
    if (isc_buffer_availablelength(b) <= len)
        return (ISC_R_NOSPACE);
    isc_buffer_putmem(b, (const unsigned char *)s, len);
    return (ISC_R_SUCCESS);
}

/*
 * Convert a resolv.conf file into a config structure.
 */
isc_result_t
ns_lwresd_parseeresolvconf(isc_mem_t *mctx, cfg_parser_t *pctx,
               cfg_obj_t **configp)
{
    char text[4096];
    char str[16];
    isc_buffer_t b;
    lwres_context_t *lwctx = NULL;
    lwres_conf_t *lwc = NULL;
    isc_sockaddr_t sa;
    isc_netaddr_t na;
    int i;
    isc_result_t result;
    lwres_result_t lwresult;

    lwctx = NULL;
    lwresult = lwres_context_create(&lwctx, mctx, ns__lwresd_memalloc,
                    ns__lwresd_memfree,
                    LWRES_CONTEXT_SERVERMODE);
    if (lwresult != LWRES_R_SUCCESS) {
        result = ISC_R_NOMEMORY;
        goto cleanup;
    }

    lwresult = lwres_conf_parse(lwctx, lwresd_g_resolvconffile);
    if (lwresult != LWRES_R_SUCCESS) {
        result = DNS_R_SYNTAX;
        goto cleanup;
    }

    lwc = lwres_conf_get(lwctx);
    INSIST(lwc != NULL);

    isc_buffer_init(&b, text, sizeof(text));

    CHECK(buffer_putstr(&b, "options {\n"));

    /*
     * Build the list of forwarders.
     */
    if (lwc->nsnext > 0) {
        CHECK(buffer_putstr(&b, "\tforwarders {\n"));

        for (i = 0; i < lwc->nsnext; i++) {
            CHECK(lwaddr_sockaddr_fromlwresaddr(
                            &sa,
                            &lwc->nameservers[i],
                            ns_g_port));
            isc_netaddr_fromsockaddr(&na, &sa);
            CHECK(buffer_putstr(&b, "\t\t"));
            CHECK(isc_netaddr_totext(&na, &b));
            CHECK(buffer_putstr(&b, ";\n"));
        }
        CHECK(buffer_putstr(&b, "\t};\n"));
    }

    /*
     * Build the sortlist
     */
    if (lwc->sortlistnxt > 0) {
        CHECK(buffer_putstr(&b, "\tsortlist {\n"));
        CHECK(buffer_putstr(&b, "\t\t{\n"));
        CHECK(buffer_putstr(&b, "\t\t\tany;\n"));
        CHECK(buffer_putstr(&b, "\t\t\t{\n"));
        for (i = 0; i < lwc->sortlistnxt; i++) {
            lwres_addr_t *lwaddr = &lwc->sortlist[i].addr;
            lwres_addr_t *lwmask = &lwc->sortlist[i].mask;
            unsigned int mask;

            CHECK(lwaddr_sockaddr_fromlwresaddr(&sa, lwmask, 0));
            isc_netaddr_fromsockaddr(&na, &sa);
            result = isc_netaddr_masktoprefixlen(&na, &mask);
            if (result != ISC_R_SUCCESS) {
                char addrtext[ISC_NETADDR_FORMATSIZE];
                isc_netaddr_format(&na, addrtext,
                           sizeof(addrtext));
                isc_log_write(ns_g_lctx,
                          NS_LOGCATEGORY_GENERAL,
                          NS_LOGMODULE_LWRESD,
                          ISC_LOG_ERROR,
                          "processing sortlist: '%s' is "
                          "not a valid netmask",
                          addrtext);
                goto cleanup;
            }

            CHECK(lwaddr_sockaddr_fromlwresaddr(&sa, lwaddr, 0));
            isc_netaddr_fromsockaddr(&na, &sa);

            CHECK(buffer_putstr(&b, "\t\t\t\t"));
            CHECK(isc_netaddr_totext(&na, &b));
            snprintf(str, sizeof(str), "%u", mask);
            CHECK(buffer_putstr(&b, "/"));
            CHECK(buffer_putstr(&b, str));
            CHECK(buffer_putstr(&b, ";\n"));
        }
        CHECK(buffer_putstr(&b, "\t\t\t};\n"));
        CHECK(buffer_putstr(&b, "\t\t};\n"));
        CHECK(buffer_putstr(&b, "\t};\n"));
    }

    CHECK(buffer_putstr(&b, "};\n\n"));

    CHECK(buffer_putstr(&b, "lwres {\n"));

    /*
     * Build the search path
     */
    if (lwc->searchnxt > 0) {
        if (lwc->searchnxt > 0) {
            CHECK(buffer_putstr(&b, "\tsearch {\n"));
            for (i = 0; i < lwc->searchnxt; i++) {
                CHECK(buffer_putstr(&b, "\t\t\""));
                CHECK(buffer_putstr(&b, lwc->search[i]));
                CHECK(buffer_putstr(&b, "\";\n"));
            }
            CHECK(buffer_putstr(&b, "\t};\n"));
        }
    }

    /*
     * Build the ndots line
     */
    if (lwc->ndots != 1) {
        CHECK(buffer_putstr(&b, "\tndots "));
        snprintf(str, sizeof(str), "%u", lwc->ndots);
        CHECK(buffer_putstr(&b, str));
        CHECK(buffer_putstr(&b, ";\n"));
    }

    /*
     * Build the listen-on line
     */
    if (lwc->lwnext > 0) {
        CHECK(buffer_putstr(&b, "\tlisten-on {\n"));

        for (i = 0; i < lwc->lwnext; i++) {
            CHECK(lwaddr_sockaddr_fromlwresaddr(&sa,
                                &lwc->lwservers[i],
                                0));
            isc_netaddr_fromsockaddr(&na, &sa);
            CHECK(buffer_putstr(&b, "\t\t"));
            CHECK(isc_netaddr_totext(&na, &b));
            CHECK(buffer_putstr(&b, ";\n"));
        }
        CHECK(buffer_putstr(&b, "\t};\n"));
    }

    CHECK(buffer_putstr(&b, "};\n"));

#if 0
    printf("%.*s\n",
           (int)isc_buffer_usedlength(&b),
           (char *)isc_buffer_base(&b));
#endif

    lwres_conf_clear(lwctx);
    lwres_context_destroy(&lwctx);

    return (cfg_parse_buffer(pctx, &b, &cfg_type_namedconf, configp));

 cleanup:

    if (lwctx != NULL) {
        lwres_conf_clear(lwctx);
        lwres_context_destroy(&lwctx);
    }

    return (result);
}


/*
 * Handle lwresd manager objects
 */
isc_result_t
ns_lwdmanager_create(isc_mem_t *mctx, const cfg_obj_t *lwres,
             ns_lwresd_t **lwresdp)
{
    ns_lwresd_t *lwresd;
    const char *vname;
    dns_rdataclass_t vclass;
    const cfg_obj_t *obj, *viewobj, *searchobj;
    const cfg_listelt_t *element;
    isc_result_t result;

    INSIST(lwresdp != NULL && *lwresdp == NULL);

    lwresd = isc_mem_get(mctx, sizeof(ns_lwresd_t));
    if (lwresd == NULL)
        return (ISC_R_NOMEMORY);

    lwresd->mctx = NULL;
    isc_mem_attach(mctx, &lwresd->mctx);
    lwresd->view = NULL;
    lwresd->search = NULL;
    lwresd->refs = 1;

    obj = NULL;
    (void)cfg_map_get(lwres, "ndots", &obj);
    if (obj != NULL)
        lwresd->ndots = cfg_obj_asuint32(obj);
    else
        lwresd->ndots = 1;

    RUNTIME_CHECK(isc_mutex_init(&lwresd->lock) == ISC_R_SUCCESS);

    lwresd->shutting_down = ISC_FALSE;

    viewobj = NULL;
    (void)cfg_map_get(lwres, "view", &viewobj);
    if (viewobj != NULL) {
        vname = cfg_obj_asstring(cfg_tuple_get(viewobj, "name"));
        obj = cfg_tuple_get(viewobj, "class");
        result = ns_config_getclass(obj, dns_rdataclass_in, &vclass);
        if (result != ISC_R_SUCCESS)
            goto fail;
    } else {
        vname = "_default";
        vclass = dns_rdataclass_in;
    }

    result = dns_viewlist_find(&ns_g_server->viewlist, vname, vclass,
                   &lwresd->view);
    if (result != ISC_R_SUCCESS) {
        isc_log_write(ns_g_lctx, NS_LOGCATEGORY_GENERAL,
                  NS_LOGMODULE_LWRESD, ISC_LOG_WARNING,
                  "couldn't find view %s", vname);
        goto fail;
    }

    searchobj = NULL;
    (void)cfg_map_get(lwres, "search", &searchobj);
    if (searchobj != NULL) {
        lwresd->search = NULL;
        result = ns_lwsearchlist_create(lwresd->mctx,
                        &lwresd->search);
        if (result != ISC_R_SUCCESS) {
            isc_log_write(ns_g_lctx, NS_LOGCATEGORY_GENERAL,
                      NS_LOGMODULE_LWRESD, ISC_LOG_WARNING,
                      "couldn't create searchlist");
            goto fail;
        }
        for (element = cfg_list_first(searchobj);
             element != NULL;
             element = cfg_list_next(element))
        {
            const cfg_obj_t *search;
            const char *searchstr;
            isc_buffer_t namebuf;
            dns_fixedname_t fname;
            dns_name_t *name;

            search = cfg_listelt_value(element);
            searchstr = cfg_obj_asstring(search);

            dns_fixedname_init(&fname);
            name = dns_fixedname_name(&fname);
            isc_buffer_constinit(&namebuf, searchstr,
                    strlen(searchstr));
            isc_buffer_add(&namebuf, strlen(searchstr));
            result = dns_name_fromtext(name, &namebuf,
                           dns_rootname, 0, NULL);
            if (result != ISC_R_SUCCESS) {
                isc_log_write(ns_g_lctx,
                          NS_LOGCATEGORY_GENERAL,
                          NS_LOGMODULE_LWRESD,
                          ISC_LOG_WARNING,
                          "invalid name %s in searchlist",
                          searchstr);
                continue;
            }

            result = ns_lwsearchlist_append(lwresd->search, name);
            if (result != ISC_R_SUCCESS) {
                isc_log_write(ns_g_lctx,
                          NS_LOGCATEGORY_GENERAL,
                          NS_LOGMODULE_LWRESD,
                          ISC_LOG_WARNING,
                          "couldn't update searchlist");
                goto fail;
            }
        }
    }

    obj = NULL;
    (void)cfg_map_get(lwres, "lwres-tasks", &obj);
    if (obj != NULL)
        lwresd->ntasks = cfg_obj_asuint32(obj);
    else
        lwresd->ntasks = ns_g_cpus;

    if (lwresd->ntasks == 0)
        lwresd->ntasks = 1;

    obj = NULL;
    (void)cfg_map_get(lwres, "lwres-clients", &obj);
    if (obj != NULL) {
        lwresd->nclients = cfg_obj_asuint32(obj);
        if (lwresd->nclients > LWRESD_NCLIENTS_MAX)
            lwresd->nclients = LWRESD_NCLIENTS_MAX;
    } else if (ns_g_lwresdonly)
        lwresd->nclients = 1024;
    else
        lwresd->nclients = 256;

    lwresd->magic = LWRESD_MAGIC;

    *lwresdp = lwresd;
    return (ISC_R_SUCCESS);

 fail:
    if (lwresd->view != NULL)
        dns_view_detach(&lwresd->view);
    if (lwresd->search != NULL)
        ns_lwsearchlist_detach(&lwresd->search);
    if (lwresd->mctx != NULL)
        isc_mem_detach(&lwresd->mctx);
    isc_mem_put(mctx, lwresd, sizeof(ns_lwresd_t));
    return (result);
}

void
ns_lwdmanager_attach(ns_lwresd_t *source, ns_lwresd_t **targetp) {
    INSIST(VALID_LWRESD(source));
    INSIST(targetp != NULL && *targetp == NULL);

    LOCK(&source->lock);
    source->refs++;
    UNLOCK(&source->lock);

    *targetp = source;
}

void
ns_lwdmanager_detach(ns_lwresd_t **lwresdp) {
    ns_lwresd_t *lwresd;
    isc_mem_t *mctx;
    isc_boolean_t done = ISC_FALSE;

    INSIST(lwresdp != NULL && *lwresdp != NULL);
    INSIST(VALID_LWRESD(*lwresdp));

    lwresd = *lwresdp;
    *lwresdp = NULL;

    LOCK(&lwresd->lock);
    INSIST(lwresd->refs > 0);
    lwresd->refs--;
    if (lwresd->refs == 0)
        done = ISC_TRUE;
    UNLOCK(&lwresd->lock);

    if (!done)
        return;

    dns_view_detach(&lwresd->view);
    if (lwresd->search != NULL)
        ns_lwsearchlist_detach(&lwresd->search);
    mctx = lwresd->mctx;
    lwresd->magic = 0;
    isc_mem_put(mctx, lwresd, sizeof(*lwresd));
    isc_mem_detach(&mctx);
}


/*
 * Handle listener objects
 */
void
ns_lwreslistener_attach(ns_lwreslistener_t *source,
            ns_lwreslistener_t **targetp)
{
    INSIST(VALID_LWRESLISTENER(source));
    INSIST(targetp != NULL && *targetp == NULL);

    LOCK(&source->lock);
    source->refs++;
    UNLOCK(&source->lock);

    *targetp = source;
}

void
ns_lwreslistener_detach(ns_lwreslistener_t **listenerp) {
    ns_lwreslistener_t *listener;
    isc_mem_t *mctx;
    isc_boolean_t done = ISC_FALSE;

    INSIST(listenerp != NULL && *listenerp != NULL);
    INSIST(VALID_LWRESLISTENER(*listenerp));

    listener = *listenerp;

    LOCK(&listener->lock);
    INSIST(listener->refs > 0);
    listener->refs--;
    if (listener->refs == 0)
        done = ISC_TRUE;
    UNLOCK(&listener->lock);

    if (!done)
        return;

    if (listener->manager != NULL)
        ns_lwdmanager_detach(&listener->manager);

    if (listener->sock != NULL)
        isc_socket_detach(&listener->sock);

    listener->magic = 0;
    mctx = listener->mctx;
    isc_mem_put(mctx, listener, sizeof(*listener));
    isc_mem_detach(&mctx);
    listenerp = NULL;
}

static isc_result_t
listener_create(isc_mem_t *mctx, ns_lwresd_t *lwresd,
        ns_lwreslistener_t **listenerp)
{
    ns_lwreslistener_t *listener;
    isc_result_t result;

    REQUIRE(listenerp != NULL && *listenerp == NULL);

    listener = isc_mem_get(mctx, sizeof(ns_lwreslistener_t));
    if (listener == NULL)
        return (ISC_R_NOMEMORY);

    result = isc_mutex_init(&listener->lock);
    if (result != ISC_R_SUCCESS) {
        isc_mem_put(mctx, listener, sizeof(ns_lwreslistener_t));
        return (result);
    }

    listener->magic = LWRESLISTENER_MAGIC;
    listener->refs = 1;

    listener->sock = NULL;

    listener->manager = NULL;
    ns_lwdmanager_attach(lwresd, &listener->manager);

    listener->mctx = NULL;
    isc_mem_attach(mctx, &listener->mctx);

    ISC_LINK_INIT(listener, link);
    ISC_LIST_INIT(listener->cmgrs);

    *listenerp = listener;
    return (ISC_R_SUCCESS);
}

static isc_result_t
listener_bind(ns_lwreslistener_t *listener, isc_sockaddr_t *address) {
    isc_socket_t *sock = NULL;
    isc_result_t result = ISC_R_SUCCESS;
    int pf;

    pf = isc_sockaddr_pf(address);
    if ((pf == AF_INET && isc_net_probeipv4() != ISC_R_SUCCESS) ||
        (pf == AF_INET6 && isc_net_probeipv6() != ISC_R_SUCCESS))
        return (ISC_R_FAMILYNOSUPPORT);

    listener->address = *address;

    if (isc_sockaddr_getport(&listener->address) == 0) {
        in_port_t port;
        port = lwresd_g_listenport;
        if (port == 0)
            port = LWRES_UDP_PORT;
        isc_sockaddr_setport(&listener->address, port);
    }

    sock = NULL;
    result = isc_socket_create(ns_g_socketmgr, pf,
                   isc_sockettype_udp, &sock);
    if (result != ISC_R_SUCCESS) {
        isc_log_write(ns_g_lctx, NS_LOGCATEGORY_GENERAL,
                  NS_LOGMODULE_LWRESD, ISC_LOG_WARNING,
                  "failed to create lwres socket: %s",
                  isc_result_totext(result));
        return (result);
    }

    result = isc_socket_bind(sock, &listener->address,
                 ISC_SOCKET_REUSEADDRESS);
    if (result != ISC_R_SUCCESS) {
        char socktext[ISC_SOCKADDR_FORMATSIZE];
        isc_sockaddr_format(&listener->address, socktext,
                    sizeof(socktext));
        isc_socket_detach(&sock);
        isc_log_write(ns_g_lctx, NS_LOGCATEGORY_GENERAL,
                  NS_LOGMODULE_LWRESD, ISC_LOG_WARNING,
                  "failed to add lwres socket: %s: %s",
                  socktext, isc_result_totext(result));
        return (result);
    }
    listener->sock = sock;
    return (ISC_R_SUCCESS);
}

static void
listener_copysock(ns_lwreslistener_t *oldlistener,
          ns_lwreslistener_t *newlistener)
{
    newlistener->address = oldlistener->address;
    isc_socket_attach(oldlistener->sock, &newlistener->sock);
}

static isc_result_t
listener_startclients(ns_lwreslistener_t *listener) {
    ns_lwdclientmgr_t *cm, *next;
    unsigned int i;
    isc_result_t result = ISC_R_SUCCESS;

    isc_log_write(ns_g_lctx, NS_LOGCATEGORY_GENERAL,
              NS_LOGMODULE_LWRESD, ISC_LOG_DEBUG(6),
              "listener_startclients: creating %d "
              "managers with %d clients each",
              listener->manager->ntasks, listener->manager->nclients);

    /*
     * Create the client managers.
     */
    for (i = 0; i < listener->manager->ntasks; i++) {
        result = ns_lwdclientmgr_create(listener,
                        listener->manager->nclients,
                        ns_g_taskmgr);
        if (result != ISC_R_SUCCESS)
            break;
    }

    /*
     * If the list is empty return now with the previous
     * ns_lwdclientmgr_create() result.
     */
    if (ISC_LIST_EMPTY(listener->cmgrs))
        return (result);

    /*
     * Walk the list of clients and start each one up.
     */
    LOCK(&listener->lock);
    cm = ISC_LIST_HEAD(listener->cmgrs);
    while (cm != NULL) {
        next = ISC_LIST_NEXT(cm, link);
        result = ns_lwdclient_startrecv(cm);
        if (result != ISC_R_SUCCESS)
            isc_log_write(ns_g_lctx, NS_LOGCATEGORY_GENERAL,
                      NS_LOGMODULE_LWRESD, ISC_LOG_ERROR,
                      "could not start lwres "
                      "client handler: %s",
                      isc_result_totext(result));
        cm = next;
    }
    UNLOCK(&listener->lock);

    return (ISC_R_SUCCESS);
}

static void
listener_shutdown(ns_lwreslistener_t *listener) {
    ns_lwdclientmgr_t *cm;

    cm = ISC_LIST_HEAD(listener->cmgrs);
    while (cm != NULL) {
        isc_task_shutdown(cm->task);
        cm = ISC_LIST_NEXT(cm, link);
    }
}

static isc_result_t
find_listener(isc_sockaddr_t *address, ns_lwreslistener_t **listenerp) {
    ns_lwreslistener_t *listener;

    INSIST(listenerp != NULL && *listenerp == NULL);

    for (listener = ISC_LIST_HEAD(listeners);
         listener != NULL;
         listener = ISC_LIST_NEXT(listener, link))
    {
        if (!isc_sockaddr_equal(address, &listener->address))
            continue;
        *listenerp = listener;
        return (ISC_R_SUCCESS);
    }
    return (ISC_R_NOTFOUND);
}

void
ns_lwreslistener_unlinkcm(ns_lwreslistener_t *listener, ns_lwdclientmgr_t *cm)
{
    REQUIRE(VALID_LWRESLISTENER(listener));

    LOCK(&listener->lock);
    ISC_LIST_UNLINK(listener->cmgrs, cm, link);
    UNLOCK(&listener->lock);
}

void
ns_lwreslistener_linkcm(ns_lwreslistener_t *listener, ns_lwdclientmgr_t *cm) {
    REQUIRE(VALID_LWRESLISTENER(listener));

    /*
     * This does no locking, since it's called early enough that locking
     * isn't needed.
     */
    ISC_LIST_APPEND(listener->cmgrs, cm, link);
}

static isc_result_t
configure_listener(isc_sockaddr_t *address, ns_lwresd_t *lwresd,
           isc_mem_t *mctx, ns_lwreslistenerlist_t *newlisteners)
{
    ns_lwreslistener_t *listener, *oldlistener = NULL;
    char socktext[ISC_SOCKADDR_FORMATSIZE];
    isc_result_t result;

    (void)find_listener(address, &oldlistener);
    listener = NULL;
    result = listener_create(mctx, lwresd, &listener);
    if (result != ISC_R_SUCCESS) {
        isc_sockaddr_format(address, socktext, sizeof(socktext));
        isc_log_write(ns_g_lctx, ISC_LOGCATEGORY_GENERAL,
                  NS_LOGMODULE_LWRESD, ISC_LOG_WARNING,
                  "lwres failed to configure %s: %s",
                  socktext, isc_result_totext(result));
        return (result);
    }

    /*
     * If there's already a listener, don't rebind the socket.
     */
    if (oldlistener == NULL) {
        result = listener_bind(listener, address);
        if (result != ISC_R_SUCCESS) {
            ns_lwreslistener_detach(&listener);
            return (ISC_R_SUCCESS);
        }
    } else
        listener_copysock(oldlistener, listener);

    result = listener_startclients(listener);
    if (result != ISC_R_SUCCESS) {
        isc_sockaddr_format(address, socktext, sizeof(socktext));
        isc_log_write(ns_g_lctx, ISC_LOGCATEGORY_GENERAL,
                  NS_LOGMODULE_LWRESD, ISC_LOG_WARNING,
                  "lwres: failed to start %s: %s", socktext,
                  isc_result_totext(result));
        ns_lwreslistener_detach(&listener);
        return (ISC_R_SUCCESS);
    }

    if (oldlistener != NULL) {
        /*
         * Remove the old listener from the old list and shut it down.
         */
        ISC_LIST_UNLINK(listeners, oldlistener, link);
        listener_shutdown(oldlistener);
        ns_lwreslistener_detach(&oldlistener);
    } else {
        isc_sockaddr_format(address, socktext, sizeof(socktext));
        isc_log_write(ns_g_lctx, ISC_LOGCATEGORY_GENERAL,
                  NS_LOGMODULE_LWRESD, ISC_LOG_NOTICE,
                  "lwres listening on %s", socktext);
    }

    ISC_LIST_APPEND(*newlisteners, listener, link);
    return (result);
}

isc_result_t
ns_lwresd_configure(isc_mem_t *mctx, const cfg_obj_t *config) {
    const cfg_obj_t *lwreslist = NULL;
    const cfg_obj_t *lwres = NULL;
    const cfg_obj_t *listenerslist = NULL;
    const cfg_listelt_t *element = NULL;
    ns_lwreslistener_t *listener;
    ns_lwreslistenerlist_t newlisteners;
    isc_result_t result;
    char socktext[ISC_SOCKADDR_FORMATSIZE];
    isc_sockaddr_t *addrs = NULL;
    ns_lwresd_t *lwresd = NULL;
    isc_uint32_t count = 0;

    REQUIRE(mctx != NULL);
    REQUIRE(config != NULL);

    RUNTIME_CHECK(isc_once_do(&once, initialize_mutex) == ISC_R_SUCCESS);

    ISC_LIST_INIT(newlisteners);

    result = cfg_map_get(config, "lwres", &lwreslist);
    if (result != ISC_R_SUCCESS)
        return (ISC_R_SUCCESS);

    LOCK(&listeners_lock);
    /*
     * Run through the new lwres address list, noting sockets that
     * are already being listened on and moving them to the new list.
     *
     * Identifying duplicates addr/port combinations is left to either
     * the underlying config code, or to the bind attempt getting an
     * address-in-use error.
     */
    for (element = cfg_list_first(lwreslist);
         element != NULL;
         element = cfg_list_next(element))
    {
        in_port_t port;

        lwres = cfg_listelt_value(element);
        CHECK(ns_lwdmanager_create(mctx, lwres, &lwresd));

        port = lwresd_g_listenport;
        if (port == 0)
            port = LWRES_UDP_PORT;

        listenerslist = NULL;
        (void)cfg_map_get(lwres, "listen-on", &listenerslist);
        if (listenerslist == NULL) {
            struct in_addr localhost;
            isc_sockaddr_t address;

            localhost.s_addr = htonl(INADDR_LOOPBACK);
            isc_sockaddr_fromin(&address, &localhost, port);
            CHECK(configure_listener(&address, lwresd, mctx,
                         &newlisteners));
        } else {
            isc_uint32_t i;

            CHECK(ns_config_getiplist(config, listenerslist,
                          port, mctx, &addrs, NULL,
                          &count));
            for (i = 0; i < count; i++)
                CHECK(configure_listener(&addrs[i], lwresd,
                             mctx, &newlisteners));
            ns_config_putiplist(mctx, &addrs, NULL, count);
        }
        ns_lwdmanager_detach(&lwresd);
    }

    /*
     * Shutdown everything on the listeners list, and remove them from
     * the list.  Then put all of the new listeners on it.
     */

    while (!ISC_LIST_EMPTY(listeners)) {
        listener = ISC_LIST_HEAD(listeners);
        ISC_LIST_UNLINK(listeners, listener, link);

        isc_sockaddr_format(&listener->address,
                    socktext, sizeof(socktext));

        listener_shutdown(listener);
        ns_lwreslistener_detach(&listener);

        isc_log_write(ns_g_lctx, ISC_LOGCATEGORY_GENERAL,
                  NS_LOGMODULE_LWRESD, ISC_LOG_NOTICE,
                  "lwres no longer listening on %s", socktext);
    }

 cleanup:
    ISC_LIST_APPENDLIST(listeners, newlisteners, link);

    if (addrs != NULL)
        ns_config_putiplist(mctx, &addrs, NULL, count);

    if (lwresd != NULL)
        ns_lwdmanager_detach(&lwresd);

    UNLOCK(&listeners_lock);

    return (result);
}

void
ns_lwresd_shutdown(void) {
    ns_lwreslistener_t *listener;

    RUNTIME_CHECK(isc_once_do(&once, initialize_mutex) == ISC_R_SUCCESS);

    while (!ISC_LIST_EMPTY(listeners)) {
        listener = ISC_LIST_HEAD(listeners);
        ISC_LIST_UNLINK(listeners, listener, link);
        ns_lwreslistener_detach(&listener);
    }
}