dispatch.c

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/*
 * Copyright (C) 2004-2009, 2011-2015  Internet Systems Consortium, Inc. ("ISC")
 * Copyright (C) 1999-2003  Internet Software Consortium.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

/*! \file */

#include <config.h>

#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

#include <isc/entropy.h>
#include <isc/mem.h>
#include <isc/mutex.h>
#include <isc/portset.h>
#include <isc/print.h>
#include <isc/random.h>
#include <isc/socket.h>
#include <isc/stats.h>
#include <isc/string.h>
#include <isc/task.h>
#include <isc/time.h>
#include <isc/util.h>

#include <dns/acl.h>
#include <dns/dispatch.h>
#include <dns/events.h>
#include <dns/log.h>
#include <dns/message.h>
#include <dns/portlist.h>
#include <dns/stats.h>
#include <dns/tcpmsg.h>
#include <dns/types.h>

typedef ISC_LIST(dns_dispentry_t)       dns_displist_t;

typedef struct dispsocket               dispsocket_t;
typedef ISC_LIST(dispsocket_t)          dispsocketlist_t;

typedef struct dispportentry            dispportentry_t;
typedef ISC_LIST(dispportentry_t)       dispportlist_t;

typedef struct dns_qid {
        unsigned int    magic;
        unsigned int    qid_nbuckets;   /*%< hash table size */
        unsigned int    qid_increment;  /*%< id increment on collision */
        isc_mutex_t     lock;
        dns_displist_t  *qid_table;     /*%< the table itself */
        dispsocketlist_t *sock_table;   /*%< socket table */
} dns_qid_t;

struct dns_dispatchmgr {
        /* Unlocked. */
        unsigned int                    magic;
        isc_mem_t                      *mctx;
        dns_acl_t                      *blackhole;
        dns_portlist_t                 *portlist;
        isc_stats_t                    *stats;
        isc_entropy_t                  *entropy; /*%< entropy source */

        /* Locked by "lock". */
        isc_mutex_t                     lock;
        unsigned int                    state;
        ISC_LIST(dns_dispatch_t)        list;

        /* Locked by rng_lock. */
        isc_mutex_t                     rng_lock;
        isc_rng_t                      *rngctx; /*%< RNG context for QID */

        /* locked by buffer_lock */
        dns_qid_t                       *qid;
        isc_mutex_t                     buffer_lock;
        unsigned int                    buffers;    /*%< allocated buffers */
        unsigned int                    buffersize; /*%< size of each buffer */
        unsigned int                    maxbuffers; /*%< max buffers */

        /* Locked internally. */
        isc_mutex_t                     depool_lock;
        isc_mempool_t                  *depool; /*%< pool for dispatch events */
        isc_mutex_t                     rpool_lock;
        isc_mempool_t                  *rpool;  /*%< pool for replies */
        isc_mutex_t                     dpool_lock;
        isc_mempool_t                  *dpool;  /*%< dispatch allocations */
        isc_mutex_t                     bpool_lock;
        isc_mempool_t                  *bpool;  /*%< pool for buffers */
        isc_mutex_t                     spool_lock;
        isc_mempool_t                  *spool;  /*%< pool for dispsocks */

        /*%
         * Locked by qid->lock if qid exists; otherwise, can be used without
         * being locked.
         * Memory footprint considerations: this is a simple implementation of
         * available ports, i.e., an ordered array of the actual port numbers.
         * This will require about 256KB of memory in the worst case (128KB for
         * each of IPv4 and IPv6).  We could reduce it by representing it as a
         * more sophisticated way such as a list (or array) of ranges that are
         * searched to identify a specific port.  Our decision here is the saved
         * memory isn't worth the implementation complexity, considering the
         * fact that the whole BIND9 process (which is mainly named) already
         * requires a pretty large memory footprint.  We may, however, have to
         * revisit the decision when we want to use it as a separate module for
         * an environment where memory requirement is severer.
         */
        in_port_t       *v4ports;       /*%< available ports for IPv4 */
        unsigned int    nv4ports;       /*%< # of available ports for IPv4 */
        in_port_t       *v6ports;       /*%< available ports for IPv4 */
        unsigned int    nv6ports;       /*%< # of available ports for IPv4 */
};

#define MGR_SHUTTINGDOWN                0x00000001U
#define MGR_IS_SHUTTINGDOWN(l)  (((l)->state & MGR_SHUTTINGDOWN) != 0)

#define IS_PRIVATE(d)   (((d)->attributes & DNS_DISPATCHATTR_PRIVATE) != 0)

struct dns_dispentry {
        unsigned int                    magic;
        dns_dispatch_t                 *disp;
        dns_messageid_t                 id;
        in_port_t                       port;
        unsigned int                    bucket;
        isc_sockaddr_t                  host;
        isc_task_t                     *task;
        isc_taskaction_t                action;
        void                           *arg;
        isc_boolean_t                   item_out;
        dispsocket_t                    *dispsocket;
        ISC_LIST(dns_dispatchevent_t)   items;
        ISC_LINK(dns_dispentry_t)       link;
};

/*%
 * Maximum number of dispatch sockets that can be pooled for reuse.  The
 * appropriate value may vary, but experiments have shown a busy caching server
 * may need more than 1000 sockets concurrently opened.  The maximum allowable
 * number of dispatch sockets (per manager) will be set to the double of this
 * value.
 */
#ifndef DNS_DISPATCH_POOLSOCKS
#define DNS_DISPATCH_POOLSOCKS                  2048
#endif

/*%
 * Quota to control the number of dispatch sockets.  If a dispatch has more
 * than the quota of sockets, new queries will purge oldest ones, so that
 * a massive number of outstanding queries won't prevent subsequent queries
 * (especially if the older ones take longer time and result in timeout).
 */
#ifndef DNS_DISPATCH_SOCKSQUOTA
#define DNS_DISPATCH_SOCKSQUOTA                 3072
#endif

struct dispsocket {
        unsigned int                    magic;
        isc_socket_t                    *socket;
        dns_dispatch_t                  *disp;
        isc_sockaddr_t                  host;
        in_port_t                       localport; /* XXX: should be removed later */
        dispportentry_t                 *portentry;
        dns_dispentry_t                 *resp;
        isc_task_t                      *task;
        ISC_LINK(dispsocket_t)          link;
        unsigned int                    bucket;
        ISC_LINK(dispsocket_t)          blink;
};

/*%
 * A port table entry.  We remember every port we first open in a table with a
 * reference counter so that we can 'reuse' the same port (with different
 * destination addresses) using the SO_REUSEADDR socket option.
 */
struct dispportentry {
        in_port_t                       port;
        unsigned int                    refs;
        ISC_LINK(struct dispportentry)  link;
};

#ifndef DNS_DISPATCH_PORTTABLESIZE
#define DNS_DISPATCH_PORTTABLESIZE      1024
#endif

#define INVALID_BUCKET          (0xffffdead)

/*%
 * Number of tasks for each dispatch that use separate sockets for different
 * transactions.  This must be a power of 2 as it will divide 32 bit numbers
 * to get an uniformly random tasks selection.  See get_dispsocket().
 */
#define MAX_INTERNAL_TASKS      64

struct dns_dispatch {
        /* Unlocked. */
        unsigned int            magic;          /*%< magic */
        dns_dispatchmgr_t      *mgr;            /*%< dispatch manager */
        int                     ntasks;
        /*%
         * internal task buckets.  We use multiple tasks to distribute various
         * socket events well when using separate dispatch sockets.  We use the
         * 1st task (task[0]) for internal control events.
         */
        isc_task_t             *task[MAX_INTERNAL_TASKS];
        isc_socket_t           *socket;         /*%< isc socket attached to */
        isc_sockaddr_t          local;          /*%< local address */
        in_port_t               localport;      /*%< local UDP port */
        isc_sockaddr_t          peer;           /*%< peer address (TCP) */
        isc_dscp_t              dscp;           /*%< "listen-on" DSCP value */
        unsigned int            maxrequests;    /*%< max requests */
        isc_event_t            *ctlevent;

        isc_mutex_t             sepool_lock;
        isc_mempool_t          *sepool;         /*%< pool for socket events */

        /*% Locked by mgr->lock. */
        ISC_LINK(dns_dispatch_t) link;

        /* Locked by "lock". */
        isc_mutex_t             lock;           /*%< locks all below */
        isc_sockettype_t        socktype;
        unsigned int            attributes;
        unsigned int            refcount;       /*%< number of users */
        dns_dispatchevent_t    *failsafe_ev;    /*%< failsafe cancel event */
        unsigned int            shutting_down : 1,
                                shutdown_out : 1,
                                connected : 1,
                                tcpmsg_valid : 1,
                                recv_pending : 1; /*%< is a recv() pending? */
        isc_result_t            shutdown_why;
        ISC_LIST(dispsocket_t)  activesockets;
        ISC_LIST(dispsocket_t)  inactivesockets;
        unsigned int            nsockets;
        unsigned int            requests;       /*%< how many requests we have */
        unsigned int            tcpbuffers;     /*%< allocated buffers */
        dns_tcpmsg_t            tcpmsg;         /*%< for tcp streams */
        dns_qid_t               *qid;
        isc_rng_t               *rngctx;        /*%< for QID/UDP port num */
        dispportlist_t          *port_table;    /*%< hold ports 'owned' by us */
        isc_mempool_t           *portpool;      /*%< port table entries  */
};

#define QID_MAGIC               ISC_MAGIC('Q', 'i', 'd', ' ')
#define VALID_QID(e)            ISC_MAGIC_VALID((e), QID_MAGIC)

#define RESPONSE_MAGIC          ISC_MAGIC('D', 'r', 's', 'p')
#define VALID_RESPONSE(e)       ISC_MAGIC_VALID((e), RESPONSE_MAGIC)

#define DISPSOCK_MAGIC          ISC_MAGIC('D', 's', 'o', 'c')
#define VALID_DISPSOCK(e)       ISC_MAGIC_VALID((e), DISPSOCK_MAGIC)

#define DISPATCH_MAGIC          ISC_MAGIC('D', 'i', 's', 'p')
#define VALID_DISPATCH(e)       ISC_MAGIC_VALID((e), DISPATCH_MAGIC)

#define DNS_DISPATCHMGR_MAGIC   ISC_MAGIC('D', 'M', 'g', 'r')
#define VALID_DISPATCHMGR(e)    ISC_MAGIC_VALID((e), DNS_DISPATCHMGR_MAGIC)

#define DNS_QID(disp) ((disp)->socktype == isc_sockettype_tcp) ? \
                       (disp)->qid : (disp)->mgr->qid
#define DISP_RNGCTX(disp) ((disp)->socktype == isc_sockettype_udp) ? \
                        ((disp)->rngctx) : ((disp)->mgr->rngctx)

/*%
 * Locking a query port buffer is a bit tricky.  We access the buffer without
 * locking until qid is created.  Technically, there is a possibility of race
 * between the creation of qid and access to the port buffer; in practice,
 * however, this should be safe because qid isn't created until the first
 * dispatch is created and there should be no contending situation until then.
 */
#define PORTBUFLOCK(mgr) if ((mgr)->qid != NULL) LOCK(&((mgr)->qid->lock))
#define PORTBUFUNLOCK(mgr) if ((mgr)->qid != NULL) UNLOCK((&(mgr)->qid->lock))

/*
 * Statics.
 */
static dns_dispentry_t *entry_search(dns_qid_t *, isc_sockaddr_t *,
                                     dns_messageid_t, in_port_t, unsigned int);
static isc_boolean_t destroy_disp_ok(dns_dispatch_t *);
static void destroy_disp(isc_task_t *task, isc_event_t *event);
static void destroy_dispsocket(dns_dispatch_t *, dispsocket_t **);
static void deactivate_dispsocket(dns_dispatch_t *, dispsocket_t *);
static void udp_exrecv(isc_task_t *, isc_event_t *);
static void udp_shrecv(isc_task_t *, isc_event_t *);
static void udp_recv(isc_event_t *, dns_dispatch_t *, dispsocket_t *);
static void tcp_recv(isc_task_t *, isc_event_t *);
static isc_result_t startrecv(dns_dispatch_t *, dispsocket_t *);
static isc_uint32_t dns_hash(dns_qid_t *, isc_sockaddr_t *, dns_messageid_t,
                             in_port_t);
static void free_buffer(dns_dispatch_t *disp, void *buf, unsigned int len);
static void *allocate_udp_buffer(dns_dispatch_t *disp);
static inline void free_devent(dns_dispatch_t *disp, dns_dispatchevent_t *ev);
static inline dns_dispatchevent_t *allocate_devent(dns_dispatch_t *disp);
static void do_cancel(dns_dispatch_t *disp);
static dns_dispentry_t *linear_first(dns_qid_t *disp);
static dns_dispentry_t *linear_next(dns_qid_t *disp,
                                    dns_dispentry_t *resp);
static void dispatch_free(dns_dispatch_t **dispp);
static isc_result_t get_udpsocket(dns_dispatchmgr_t *mgr,
                                  dns_dispatch_t *disp,
                                  isc_socketmgr_t *sockmgr,
                                  isc_sockaddr_t *localaddr,
                                  isc_socket_t **sockp,
                                  isc_socket_t *dup_socket);
static isc_result_t dispatch_createudp(dns_dispatchmgr_t *mgr,
                                       isc_socketmgr_t *sockmgr,
                                       isc_taskmgr_t *taskmgr,
                                       isc_sockaddr_t *localaddr,
                                       unsigned int maxrequests,
                                       unsigned int attributes,
                                       dns_dispatch_t **dispp,
                                       isc_socket_t *dup_socket);
static isc_boolean_t destroy_mgr_ok(dns_dispatchmgr_t *mgr);
static void destroy_mgr(dns_dispatchmgr_t **mgrp);
static isc_result_t qid_allocate(dns_dispatchmgr_t *mgr, unsigned int buckets,
                                 unsigned int increment, dns_qid_t **qidp,
                                 isc_boolean_t needaddrtable);
static void qid_destroy(isc_mem_t *mctx, dns_qid_t **qidp);
static isc_result_t open_socket(isc_socketmgr_t *mgr, isc_sockaddr_t *local,
                                unsigned int options, isc_socket_t **sockp,
                                isc_socket_t *dup_socket);
static isc_boolean_t portavailable(dns_dispatchmgr_t *mgr, isc_socket_t *sock,
                                   isc_sockaddr_t *sockaddrp);

#define LVL(x) ISC_LOG_DEBUG(x)

static void
mgr_log(dns_dispatchmgr_t *mgr, int level, const char *fmt, ...)
     ISC_FORMAT_PRINTF(3, 4);

static void
mgr_log(dns_dispatchmgr_t *mgr, int level, const char *fmt, ...) {
        char msgbuf[2048];
        va_list ap;

        if (! isc_log_wouldlog(dns_lctx, level))
                return;

        va_start(ap, fmt);
        vsnprintf(msgbuf, sizeof(msgbuf), fmt, ap);
        va_end(ap);

        isc_log_write(dns_lctx,
                      DNS_LOGCATEGORY_DISPATCH, DNS_LOGMODULE_DISPATCH,
                      level, "dispatchmgr %p: %s", mgr, msgbuf);
}

static inline void
inc_stats(dns_dispatchmgr_t *mgr, isc_statscounter_t counter) {
        if (mgr->stats != NULL)
                isc_stats_increment(mgr->stats, counter);
}

static inline void
dec_stats(dns_dispatchmgr_t *mgr, isc_statscounter_t counter) {
        if (mgr->stats != NULL)
                isc_stats_decrement(mgr->stats, counter);
}

static void
dispatch_log(dns_dispatch_t *disp, int level, const char *fmt, ...)
     ISC_FORMAT_PRINTF(3, 4);

static void
dispatch_log(dns_dispatch_t *disp, int level, const char *fmt, ...) {
        char msgbuf[2048];
        va_list ap;

        if (! isc_log_wouldlog(dns_lctx, level))
                return;

        va_start(ap, fmt);
        vsnprintf(msgbuf, sizeof(msgbuf), fmt, ap);
        va_end(ap);

        isc_log_write(dns_lctx,
                      DNS_LOGCATEGORY_DISPATCH, DNS_LOGMODULE_DISPATCH,
                      level, "dispatch %p: %s", disp, msgbuf);
}

static void
request_log(dns_dispatch_t *disp, dns_dispentry_t *resp,
            int level, const char *fmt, ...)
     ISC_FORMAT_PRINTF(4, 5);

static void
request_log(dns_dispatch_t *disp, dns_dispentry_t *resp,
            int level, const char *fmt, ...)
{
        char msgbuf[2048];
        char peerbuf[256];
        va_list ap;

        if (! isc_log_wouldlog(dns_lctx, level))
                return;

        va_start(ap, fmt);
        vsnprintf(msgbuf, sizeof(msgbuf), fmt, ap);
        va_end(ap);

        if (VALID_RESPONSE(resp)) {
                isc_sockaddr_format(&resp->host, peerbuf, sizeof(peerbuf));
                isc_log_write(dns_lctx, DNS_LOGCATEGORY_DISPATCH,
                              DNS_LOGMODULE_DISPATCH, level,
                              "dispatch %p response %p %s: %s", disp, resp,
                              peerbuf, msgbuf);
        } else {
                isc_log_write(dns_lctx, DNS_LOGCATEGORY_DISPATCH,
                              DNS_LOGMODULE_DISPATCH, level,
                              "dispatch %p req/resp %p: %s", disp, resp,
                              msgbuf);
        }
}

/*
 * Return a hash of the destination and message id.
 */
static isc_uint32_t
dns_hash(dns_qid_t *qid, isc_sockaddr_t *dest, dns_messageid_t id,
         in_port_t port)
{
        unsigned int ret;

        ret = isc_sockaddr_hash(dest, ISC_TRUE);
        ret ^= (id << 16) | port;
        ret %= qid->qid_nbuckets;

        INSIST(ret < qid->qid_nbuckets);

        return (ret);
}

/*
 * Find the first entry in 'qid'.  Returns NULL if there are no entries.
 */
static dns_dispentry_t *
linear_first(dns_qid_t *qid) {
        dns_dispentry_t *ret;
        unsigned int bucket;

        bucket = 0;

        while (bucket < qid->qid_nbuckets) {
                ret = ISC_LIST_HEAD(qid->qid_table[bucket]);
                if (ret != NULL)
                        return (ret);
                bucket++;
        }

        return (NULL);
}

/*
 * Find the next entry after 'resp' in 'qid'.  Return NULL if there are
 * no more entries.
 */
static dns_dispentry_t *
linear_next(dns_qid_t *qid, dns_dispentry_t *resp) {
        dns_dispentry_t *ret;
        unsigned int bucket;

        ret = ISC_LIST_NEXT(resp, link);
        if (ret != NULL)
                return (ret);

        bucket = resp->bucket;
        bucket++;
        while (bucket < qid->qid_nbuckets) {
                ret = ISC_LIST_HEAD(qid->qid_table[bucket]);
                if (ret != NULL)
                        return (ret);
                bucket++;
        }

        return (NULL);
}

/*
 * The dispatch must be locked.
 */
static isc_boolean_t
destroy_disp_ok(dns_dispatch_t *disp)
{
        if (disp->refcount != 0)
                return (ISC_FALSE);

        if (disp->recv_pending != 0)
                return (ISC_FALSE);

        if (!ISC_LIST_EMPTY(disp->activesockets))
                return (ISC_FALSE);

        if (disp->shutting_down == 0)
                return (ISC_FALSE);

        return (ISC_TRUE);
}

/*
 * Called when refcount reaches 0 (and safe to destroy).
 *
 * The dispatcher must be locked.
 * The manager must not be locked.
 */
static void
destroy_disp(isc_task_t *task, isc_event_t *event) {
        dns_dispatch_t *disp;
        dns_dispatchmgr_t *mgr;
        isc_boolean_t killmgr;
        dispsocket_t *dispsocket;
        int i;

        INSIST(event->ev_type == DNS_EVENT_DISPATCHCONTROL);

        UNUSED(task);

        disp = event->ev_arg;
        mgr = disp->mgr;

        LOCK(&mgr->lock);
        ISC_LIST_UNLINK(mgr->list, disp, link);

        dispatch_log(disp, LVL(90),
                     "shutting down; detaching from sock %p, task %p",
                     disp->socket, disp->task[0]); /* XXXX */

        if (disp->sepool != NULL) {
                isc_mempool_destroy(&disp->sepool);
                (void)isc_mutex_destroy(&disp->sepool_lock);
        }

        if (disp->socket != NULL)
                isc_socket_detach(&disp->socket);
        while ((dispsocket = ISC_LIST_HEAD(disp->inactivesockets)) != NULL) {
                ISC_LIST_UNLINK(disp->inactivesockets, dispsocket, link);
                destroy_dispsocket(disp, &dispsocket);
        }
        for (i = 0; i < disp->ntasks; i++)
                isc_task_detach(&disp->task[i]);
        isc_event_free(&event);

        dispatch_free(&disp);

        killmgr = destroy_mgr_ok(mgr);
        UNLOCK(&mgr->lock);
        if (killmgr)
                destroy_mgr(&mgr);
}

/*%
 * Manipulate port table per dispatch: find an entry for a given port number,
 * create a new entry, and decrement a given entry with possible clean-up.
 */
static dispportentry_t *
port_search(dns_dispatch_t *disp, in_port_t port) {
        dispportentry_t *portentry;

        REQUIRE(disp->port_table != NULL);

        portentry = ISC_LIST_HEAD(disp->port_table[port %
                                                   DNS_DISPATCH_PORTTABLESIZE]);
        while (portentry != NULL) {
                if (portentry->port == port)
                        return (portentry);
                portentry = ISC_LIST_NEXT(portentry, link);
        }

        return (NULL);
}

static dispportentry_t *
new_portentry(dns_dispatch_t *disp, in_port_t port) {
        dispportentry_t *portentry;
        dns_qid_t *qid;

        REQUIRE(disp->port_table != NULL);

        portentry = isc_mempool_get(disp->portpool);
        if (portentry == NULL)
                return (portentry);

        portentry->port = port;
        portentry->refs = 1;
        ISC_LINK_INIT(portentry, link);
        qid = DNS_QID(disp);
        LOCK(&qid->lock);
        ISC_LIST_APPEND(disp->port_table[port % DNS_DISPATCH_PORTTABLESIZE],
                        portentry, link);
        UNLOCK(&qid->lock);

        return (portentry);
}

/*%
 * The caller must not hold the qid->lock.
 */
static void
deref_portentry(dns_dispatch_t *disp, dispportentry_t **portentryp) {
        dispportentry_t *portentry = *portentryp;
        dns_qid_t *qid;

        REQUIRE(disp->port_table != NULL);
        REQUIRE(portentry != NULL && portentry->refs > 0);

        qid = DNS_QID(disp);
        LOCK(&qid->lock);
        portentry->refs--;

        if (portentry->refs == 0) {
                ISC_LIST_UNLINK(disp->port_table[portentry->port %
                                                 DNS_DISPATCH_PORTTABLESIZE],
                                portentry, link);
                isc_mempool_put(disp->portpool, portentry);
        }

        /*
         * Set '*portentryp' to NULL inside the lock so that
         * dispsock->portentry does not change in socket_search.
         */
        *portentryp = NULL;

        UNLOCK(&qid->lock);
}

/*%
 * Find a dispsocket for socket address 'dest', and port number 'port'.
 * Return NULL if no such entry exists.  Requires qid->lock to be held.
 */
static dispsocket_t *
socket_search(dns_qid_t *qid, isc_sockaddr_t *dest, in_port_t port,
              unsigned int bucket)
{
        dispsocket_t *dispsock;

        REQUIRE(VALID_QID(qid));
        REQUIRE(bucket < qid->qid_nbuckets);

        dispsock = ISC_LIST_HEAD(qid->sock_table[bucket]);

        while (dispsock != NULL) {
                if (dispsock->portentry != NULL &&
                    dispsock->portentry->port == port &&
                    isc_sockaddr_equal(dest, &dispsock->host))
                        return (dispsock);
                dispsock = ISC_LIST_NEXT(dispsock, blink);
        }

        return (NULL);
}

/*%
 * Make a new socket for a single dispatch with a random port number.
 * The caller must hold the disp->lock
 */
static isc_result_t
get_dispsocket(dns_dispatch_t *disp, isc_sockaddr_t *dest,
               isc_socketmgr_t *sockmgr, dispsocket_t **dispsockp,
               in_port_t *portp)
{
        int i;
        isc_uint32_t r;
        dns_dispatchmgr_t *mgr = disp->mgr;
        isc_socket_t *sock = NULL;
        isc_result_t result = ISC_R_FAILURE;
        in_port_t port;
        isc_sockaddr_t localaddr;
        unsigned int bucket = 0;
        dispsocket_t *dispsock;
        unsigned int nports;
        in_port_t *ports;
        unsigned int bindoptions;
        dispportentry_t *portentry = NULL;
        dns_qid_t *qid;

        if (isc_sockaddr_pf(&disp->local) == AF_INET) {
                nports = disp->mgr->nv4ports;
                ports = disp->mgr->v4ports;
        } else {
                nports = disp->mgr->nv6ports;
                ports = disp->mgr->v6ports;
        }
        if (nports == 0)
                return (ISC_R_ADDRNOTAVAIL);

        dispsock = ISC_LIST_HEAD(disp->inactivesockets);
        if (dispsock != NULL) {
                ISC_LIST_UNLINK(disp->inactivesockets, dispsock, link);
                sock = dispsock->socket;
                dispsock->socket = NULL;
        } else {
                dispsock = isc_mempool_get(mgr->spool);
                if (dispsock == NULL)
                        return (ISC_R_NOMEMORY);

                disp->nsockets++;
                dispsock->socket = NULL;
                dispsock->disp = disp;
                dispsock->resp = NULL;
                dispsock->portentry = NULL;
                isc_random_get(&r);
                dispsock->task = NULL;
                isc_task_attach(disp->task[r % disp->ntasks], &dispsock->task);
                ISC_LINK_INIT(dispsock, link);
                ISC_LINK_INIT(dispsock, blink);
                dispsock->magic = DISPSOCK_MAGIC;
        }

        /*
         * Pick up a random UDP port and open a new socket with it.  Avoid
         * choosing ports that share the same destination because it will be
         * very likely to fail in bind(2) or connect(2).
         */
        localaddr = disp->local;
        qid = DNS_QID(disp);

        for (i = 0; i < 64; i++) {
                port = ports[isc_rng_uniformrandom(DISP_RNGCTX(disp), nports)];
                isc_sockaddr_setport(&localaddr, port);

                LOCK(&qid->lock);
                bucket = dns_hash(qid, dest, 0, port);
                if (socket_search(qid, dest, port, bucket) != NULL) {
                        UNLOCK(&qid->lock);
                        continue;
                }
                UNLOCK(&qid->lock);
                bindoptions = 0;
                portentry = port_search(disp, port);

                if (portentry != NULL)
                        bindoptions |= ISC_SOCKET_REUSEADDRESS;
                result = open_socket(sockmgr, &localaddr, bindoptions, &sock,
                                     NULL);
                if (result == ISC_R_SUCCESS) {
                        if (portentry == NULL) {
                                portentry = new_portentry(disp, port);
                                if (portentry == NULL) {
                                        result = ISC_R_NOMEMORY;
                                        break;
                                }
                        } else {
                                LOCK(&qid->lock);
                                portentry->refs++;
                                UNLOCK(&qid->lock);
                        }
                        break;
                } else if (result == ISC_R_NOPERM) {
                        char buf[ISC_SOCKADDR_FORMATSIZE];
                        isc_sockaddr_format(&localaddr, buf, sizeof(buf));
                        dispatch_log(disp, ISC_LOG_WARNING,
                                     "open_socket(%s) -> %s: continuing",
                                     buf, isc_result_totext(result));
                } else if (result != ISC_R_ADDRINUSE)
                        break;
        }

        if (result == ISC_R_SUCCESS) {
                dispsock->socket = sock;
                dispsock->host = *dest;
                dispsock->portentry = portentry;
                dispsock->bucket = bucket;
                LOCK(&qid->lock);
                ISC_LIST_APPEND(qid->sock_table[bucket], dispsock, blink);
                UNLOCK(&qid->lock);
                *dispsockp = dispsock;
                *portp = port;
        } else {
                /*
                 * We could keep it in the inactive list, but since this should
                 * be an exceptional case and might be resource shortage, we'd
                 * rather destroy it.
                 */
                if (sock != NULL)
                        isc_socket_detach(&sock);
                destroy_dispsocket(disp, &dispsock);
        }

        return (result);
}

/*%
 * Destroy a dedicated dispatch socket.
 */
static void
destroy_dispsocket(dns_dispatch_t *disp, dispsocket_t **dispsockp) {
        dispsocket_t *dispsock;
        dns_qid_t *qid;

        /*
         * The dispatch must be locked.
         */

        REQUIRE(dispsockp != NULL && *dispsockp != NULL);
        dispsock = *dispsockp;
        REQUIRE(!ISC_LINK_LINKED(dispsock, link));

        disp->nsockets--;
        dispsock->magic = 0;
        if (dispsock->portentry != NULL)
                deref_portentry(disp, &dispsock->portentry);
        if (dispsock->socket != NULL)
                isc_socket_detach(&dispsock->socket);
        if (ISC_LINK_LINKED(dispsock, blink)) {
                qid = DNS_QID(disp);
                LOCK(&qid->lock);
                ISC_LIST_UNLINK(qid->sock_table[dispsock->bucket], dispsock,
                                blink);
                UNLOCK(&qid->lock);
        }
        if (dispsock->task != NULL)
                isc_task_detach(&dispsock->task);
        isc_mempool_put(disp->mgr->spool, dispsock);

        *dispsockp = NULL;
}

/*%
 * Deactivate a dedicated dispatch socket.  Move it to the inactive list for
 * future reuse unless the total number of sockets are exceeding the maximum.
 */
static void
deactivate_dispsocket(dns_dispatch_t *disp, dispsocket_t *dispsock) {
        isc_result_t result;
        dns_qid_t *qid;

        /*
         * The dispatch must be locked.
         */
        ISC_LIST_UNLINK(disp->activesockets, dispsock, link);
        if (dispsock->resp != NULL) {
                INSIST(dispsock->resp->dispsocket == dispsock);
                dispsock->resp->dispsocket = NULL;
        }

        INSIST(dispsock->portentry != NULL);
        deref_portentry(disp, &dispsock->portentry);

        if (disp->nsockets > DNS_DISPATCH_POOLSOCKS)
                destroy_dispsocket(disp, &dispsock);
        else {
                result = isc_socket_close(dispsock->socket);

                qid = DNS_QID(disp);
                LOCK(&qid->lock);
                ISC_LIST_UNLINK(qid->sock_table[dispsock->bucket], dispsock,
                                blink);
                UNLOCK(&qid->lock);

                if (result == ISC_R_SUCCESS)
                        ISC_LIST_APPEND(disp->inactivesockets, dispsock, link);
                else {
                        /*
                         * If the underlying system does not allow this
                         * optimization, destroy this temporary structure (and
                         * create a new one for a new transaction).
                         */
                        INSIST(result == ISC_R_NOTIMPLEMENTED);
                        destroy_dispsocket(disp, &dispsock);
                }
        }
}

/*
 * Find an entry for query ID 'id', socket address 'dest', and port number
 * 'port'.
 * Return NULL if no such entry exists.
 */
static dns_dispentry_t *
entry_search(dns_qid_t *qid, isc_sockaddr_t *dest, dns_messageid_t id,
             in_port_t port, unsigned int bucket)
{
        dns_dispentry_t *res;

        REQUIRE(VALID_QID(qid));
        REQUIRE(bucket < qid->qid_nbuckets);

        res = ISC_LIST_HEAD(qid->qid_table[bucket]);

        while (res != NULL) {
                if (res->id == id && isc_sockaddr_equal(dest, &res->host) &&
                    res->port == port) {
                        return (res);
                }
                res = ISC_LIST_NEXT(res, link);
        }

        return (NULL);
}

static void
free_buffer(dns_dispatch_t *disp, void *buf, unsigned int len) {
        isc_mempool_t *bpool;
        INSIST(buf != NULL && len != 0);


        switch (disp->socktype) {
        case isc_sockettype_tcp:
                INSIST(disp->tcpbuffers > 0);
                disp->tcpbuffers--;
                isc_mem_put(disp->mgr->mctx, buf, len);
                break;
        case isc_sockettype_udp:
                LOCK(&disp->mgr->buffer_lock);
                INSIST(disp->mgr->buffers > 0);
                INSIST(len == disp->mgr->buffersize);
                disp->mgr->buffers--;
                bpool = disp->mgr->bpool;
                UNLOCK(&disp->mgr->buffer_lock);
                isc_mempool_put(bpool, buf);
                break;
        default:
                INSIST(0);
                break;
        }
}

static void *
allocate_udp_buffer(dns_dispatch_t *disp) {
        isc_mempool_t *bpool;
        void *temp;

        LOCK(&disp->mgr->buffer_lock);
        bpool = disp->mgr->bpool;
        disp->mgr->buffers++;
        UNLOCK(&disp->mgr->buffer_lock);

        temp = isc_mempool_get(bpool);

        if (temp == NULL) {
                LOCK(&disp->mgr->buffer_lock);
                disp->mgr->buffers--;
                UNLOCK(&disp->mgr->buffer_lock);
        }

        return (temp);
}

static inline void
free_sevent(isc_event_t *ev) {
        isc_mempool_t *pool = ev->ev_destroy_arg;
        isc_socketevent_t *sev = (isc_socketevent_t *) ev;
        isc_mempool_put(pool, sev);
}

static inline isc_socketevent_t *
allocate_sevent(dns_dispatch_t *disp, isc_socket_t *sock,
                isc_eventtype_t type, isc_taskaction_t action, const void *arg)
{
        isc_socketevent_t *ev;
        void *deconst_arg;

        ev = isc_mempool_get(disp->sepool);
        if (ev == NULL)
                return (NULL);
        DE_CONST(arg, deconst_arg);
        ISC_EVENT_INIT(ev, sizeof(*ev), 0, NULL, type,
                       action, deconst_arg, sock,
                       free_sevent, disp->sepool);
        ev->result = ISC_R_UNSET;
        ISC_LINK_INIT(ev, ev_link);
        ISC_LIST_INIT(ev->bufferlist);
        ev->region.base = NULL;
        ev->n = 0;
        ev->offset = 0;
        ev->attributes = 0;

        return (ev);
}


static inline void
free_devent(dns_dispatch_t *disp, dns_dispatchevent_t *ev) {
        if (disp->failsafe_ev == ev) {
                INSIST(disp->shutdown_out == 1);
                disp->shutdown_out = 0;

                return;
        }

        isc_mempool_put(disp->mgr->depool, ev);
}

static inline dns_dispatchevent_t *
allocate_devent(dns_dispatch_t *disp) {
        dns_dispatchevent_t *ev;

        ev = isc_mempool_get(disp->mgr->depool);
        if (ev == NULL)
                return (NULL);
        ISC_EVENT_INIT(ev, sizeof(*ev), 0, NULL, 0,
                       NULL, NULL, NULL, NULL, NULL);

        return (ev);
}

static void
udp_exrecv(isc_task_t *task, isc_event_t *ev) {
        dispsocket_t *dispsock = ev->ev_arg;

        UNUSED(task);

        REQUIRE(VALID_DISPSOCK(dispsock));
        udp_recv(ev, dispsock->disp, dispsock);
}

static void
udp_shrecv(isc_task_t *task, isc_event_t *ev) {
        dns_dispatch_t *disp = ev->ev_arg;

        UNUSED(task);

        REQUIRE(VALID_DISPATCH(disp));
        udp_recv(ev, disp, NULL);
}

/*
 * General flow:
 *
 * If I/O result == CANCELED or error, free the buffer.
 *
 * If query, free the buffer, restart.
 *
 * If response:
 *      Allocate event, fill in details.
 *              If cannot allocate, free buffer, restart.
 *      find target.  If not found, free buffer, restart.
 *      if event queue is not empty, queue.  else, send.
 *      restart.
 */
static void
udp_recv(isc_event_t *ev_in, dns_dispatch_t *disp, dispsocket_t *dispsock) {
        isc_socketevent_t *ev = (isc_socketevent_t *)ev_in;
        dns_messageid_t id;
        isc_result_t dres;
        isc_buffer_t source;
        unsigned int flags;
        dns_dispentry_t *resp = NULL;
        dns_dispatchevent_t *rev;
        unsigned int bucket;
        isc_boolean_t killit;
        isc_boolean_t queue_response;
        dns_dispatchmgr_t *mgr;
        dns_qid_t *qid;
        isc_netaddr_t netaddr;
        int match;
        int result;
        isc_boolean_t qidlocked = ISC_FALSE;

        LOCK(&disp->lock);

        mgr = disp->mgr;
        qid = mgr->qid;

        dispatch_log(disp, LVL(90),
                     "got packet: requests %d, buffers %d, recvs %d",
                     disp->requests, disp->mgr->buffers, disp->recv_pending);

        if (dispsock == NULL && ev->ev_type == ISC_SOCKEVENT_RECVDONE) {
                /*
                 * Unless the receive event was imported from a listening
                 * interface, in which case the event type is
                 * DNS_EVENT_IMPORTRECVDONE, receive operation must be pending.
                 */
                INSIST(disp->recv_pending != 0);
                disp->recv_pending = 0;
        }

        if (dispsock != NULL &&
            (ev->result == ISC_R_CANCELED || dispsock->resp == NULL)) {
                /*
                 * dispsock->resp can be NULL if this transaction was canceled
                 * just after receiving a response.  Since this socket is
                 * exclusively used and there should be at most one receive
                 * event the canceled event should have been no effect.  So
                 * we can (and should) deactivate the socket right now.
                 */
                deactivate_dispsocket(disp, dispsock);
                dispsock = NULL;
        }

        if (disp->shutting_down) {
                /*
                 * This dispatcher is shutting down.
                 */
                free_buffer(disp, ev->region.base, ev->region.length);

                isc_event_free(&ev_in);
                ev = NULL;

                killit = destroy_disp_ok(disp);
                UNLOCK(&disp->lock);
                if (killit)
                        isc_task_send(disp->task[0], &disp->ctlevent);

                return;
        }

        if ((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0) {
                if (dispsock != NULL) {
                        resp = dispsock->resp;
                        id = resp->id;
                        if (ev->result != ISC_R_SUCCESS) {
                                /*
                                 * This is most likely a network error on a
                                 * connected socket.  It makes no sense to
                                 * check the address or parse the packet, but it
                                 * will help to return the error to the caller.
                                 */
                                goto sendresponse;
                        }
                } else {
                        free_buffer(disp, ev->region.base, ev->region.length);

                        isc_event_free(&ev_in);
                        UNLOCK(&disp->lock);
                        return;
                }
        } else if (ev->result != ISC_R_SUCCESS) {
                free_buffer(disp, ev->region.base, ev->region.length);

                if (ev->result != ISC_R_CANCELED)
                        dispatch_log(disp, ISC_LOG_ERROR,
                                     "odd socket result in udp_recv(): %s",
                                     isc_result_totext(ev->result));

                isc_event_free(&ev_in);
                UNLOCK(&disp->lock);
                return;
        }

        /*
         * If this is from a blackholed address, drop it.
         */
        isc_netaddr_fromsockaddr(&netaddr, &ev->address);
        if (disp->mgr->blackhole != NULL &&
            dns_acl_match(&netaddr, NULL, disp->mgr->blackhole,
                          NULL, &match, NULL) == ISC_R_SUCCESS &&
            match > 0)
        {
                if (isc_log_wouldlog(dns_lctx, LVL(10))) {
                        char netaddrstr[ISC_NETADDR_FORMATSIZE];
                        isc_netaddr_format(&netaddr, netaddrstr,
                                           sizeof(netaddrstr));
                        dispatch_log(disp, LVL(10),
                                     "blackholed packet from %s",
                                     netaddrstr);
                }
                free_buffer(disp, ev->region.base, ev->region.length);
                goto restart;
        }

        /*
         * Peek into the buffer to see what we can see.
         */
        isc_buffer_init(&source, ev->region.base, ev->region.length);
        isc_buffer_add(&source, ev->n);
        dres = dns_message_peekheader(&source, &id, &flags);
        if (dres != ISC_R_SUCCESS) {
                free_buffer(disp, ev->region.base, ev->region.length);
                dispatch_log(disp, LVL(10), "got garbage packet");
                goto restart;
        }

        dispatch_log(disp, LVL(92),
                     "got valid DNS message header, /QR %c, id %u",
                     ((flags & DNS_MESSAGEFLAG_QR) ? '1' : '0'), id);

        /*
         * Look at flags.  If query, drop it. If response,
         * look to see where it goes.
         */
        if ((flags & DNS_MESSAGEFLAG_QR) == 0) {
                /* query */
                free_buffer(disp, ev->region.base, ev->region.length);
                goto restart;
        }

        /*
         * Search for the corresponding response.  If we are using an exclusive
         * socket, we've already identified it and we can skip the search; but
         * the ID and the address must match the expected ones.
         */
        if (resp == NULL) {
                bucket = dns_hash(qid, &ev->address, id, disp->localport);
                LOCK(&qid->lock);
                qidlocked = ISC_TRUE;
                resp = entry_search(qid, &ev->address, id, disp->localport,
                                    bucket);
                dispatch_log(disp, LVL(90),
                             "search for response in bucket %d: %s",
                             bucket, (resp == NULL ? "not found" : "found"));

                if (resp == NULL) {
                        inc_stats(mgr, dns_resstatscounter_mismatch);
                        free_buffer(disp, ev->region.base, ev->region.length);
                        goto unlock;
                }
        } else if (resp->id != id || !isc_sockaddr_equal(&ev->address,
                                                         &resp->host)) {
                dispatch_log(disp, LVL(90),
                             "response to an exclusive socket doesn't match");
                inc_stats(mgr, dns_resstatscounter_mismatch);
                free_buffer(disp, ev->region.base, ev->region.length);
                goto unlock;
        }

        /*
         * Now that we have the original dispatch the query was sent
         * from check that the address and port the response was
         * sent to make sense.
         */
        if (disp != resp->disp) {
                isc_sockaddr_t a1;
                isc_sockaddr_t a2;

                /*
                 * Check that the socket types and ports match.
                 */
                if (disp->socktype != resp->disp->socktype ||
                    isc_sockaddr_getport(&disp->local) !=
                    isc_sockaddr_getport(&resp->disp->local)) {
                        free_buffer(disp, ev->region.base, ev->region.length);
                        goto unlock;
                }

                /*
                 * If each dispatch is bound to a different address
                 * then fail.
                 *
                 * Note under Linux a packet can be sent out via IPv4 socket
                 * and the response be received via a IPv6 socket.
                 *
                 * Requests sent out via IPv6 should always come back in
                 * via IPv6.
                 */
                if (isc_sockaddr_pf(&resp->disp->local) == PF_INET6 &&
                    isc_sockaddr_pf(&disp->local) != PF_INET6) {
                        free_buffer(disp, ev->region.base, ev->region.length);
                        goto unlock;
                }
                isc_sockaddr_anyofpf(&a1, isc_sockaddr_pf(&resp->disp->local));
                isc_sockaddr_anyofpf(&a2, isc_sockaddr_pf(&disp->local));
                if (!isc_sockaddr_eqaddr(&disp->local, &resp->disp->local) &&
                    !isc_sockaddr_eqaddr(&a1, &resp->disp->local) &&
                    !isc_sockaddr_eqaddr(&a2, &disp->local)) {
                        free_buffer(disp, ev->region.base, ev->region.length);
                        goto unlock;
                }
        }

  sendresponse:
        queue_response = resp->item_out;
        rev = allocate_devent(resp->disp);
        if (rev == NULL) {
                free_buffer(disp, ev->region.base, ev->region.length);
                goto unlock;
        }

        /*
         * At this point, rev contains the event we want to fill in, and
         * resp contains the information on the place to send it to.
         * Send the event off.
         */
        isc_buffer_init(&rev->buffer, ev->region.base, ev->region.length);
        isc_buffer_add(&rev->buffer, ev->n);
        rev->result = ev->result;
        rev->id = id;
        rev->addr = ev->address;
        rev->pktinfo = ev->pktinfo;
        rev->attributes = ev->attributes;
        if (queue_response) {
                ISC_LIST_APPEND(resp->items, rev, ev_link);
        } else {
                ISC_EVENT_INIT(rev, sizeof(*rev), 0, NULL,
                               DNS_EVENT_DISPATCH,
                               resp->action, resp->arg, resp, NULL, NULL);
                request_log(disp, resp, LVL(90),
                            "[a] Sent event %p buffer %p len %d to task %p",
                            rev, rev->buffer.base, rev->buffer.length,
                            resp->task);
                resp->item_out = ISC_TRUE;
                isc_task_send(resp->task, ISC_EVENT_PTR(&rev));
        }
 unlock:
        if (qidlocked)
                UNLOCK(&qid->lock);

        /*
         * Restart recv() to get the next packet.
         */
 restart:
        result = startrecv(disp, dispsock);
        if (result != ISC_R_SUCCESS && dispsock != NULL) {
                /*
                 * XXX: wired. There seems to be no recovery process other than
                 * deactivate this socket anyway (since we cannot start
                 * receiving, we won't be able to receive a cancel event
                 * from the user).
                 */
                deactivate_dispsocket(disp, dispsock);
        }
        isc_event_free(&ev_in);
        UNLOCK(&disp->lock);
}

/*
 * General flow:
 *
 * If I/O result == CANCELED, EOF, or error, notify everyone as the
 * various queues drain.
 *
 * If query, restart.
 *
 * If response:
 *      Allocate event, fill in details.
 *              If cannot allocate, restart.
 *      find target.  If not found, restart.
 *      if event queue is not empty, queue.  else, send.
 *      restart.
 */
static void
tcp_recv(isc_task_t *task, isc_event_t *ev_in) {
        dns_dispatch_t *disp = ev_in->ev_arg;
        dns_tcpmsg_t *tcpmsg = &disp->tcpmsg;
        dns_messageid_t id;
        isc_result_t dres;
        unsigned int flags;
        dns_dispentry_t *resp;
        dns_dispatchevent_t *rev;
        unsigned int bucket;
        isc_boolean_t killit;
        isc_boolean_t queue_response;
        dns_qid_t *qid;
        int level;
        char buf[ISC_SOCKADDR_FORMATSIZE];

        UNUSED(task);

        REQUIRE(VALID_DISPATCH(disp));

        qid = disp->qid;

        dispatch_log(disp, LVL(90),
                     "got TCP packet: requests %d, buffers %d, recvs %d",
                     disp->requests, disp->tcpbuffers, disp->recv_pending);

        LOCK(&disp->lock);

        INSIST(disp->recv_pending != 0);
        disp->recv_pending = 0;

        if (disp->refcount == 0) {
                /*
                 * This dispatcher is shutting down.  Force cancelation.
                 */
                tcpmsg->result = ISC_R_CANCELED;
        }

        if (tcpmsg->result != ISC_R_SUCCESS) {
                switch (tcpmsg->result) {
                case ISC_R_CANCELED:
                        break;

                case ISC_R_EOF:
                        dispatch_log(disp, LVL(90), "shutting down on EOF");
                        do_cancel(disp);
                        break;

                case ISC_R_CONNECTIONRESET:
                        level = ISC_LOG_INFO;
                        goto logit;

                default:
                        level = ISC_LOG_ERROR;
                logit:
                        isc_sockaddr_format(&tcpmsg->address, buf, sizeof(buf));
                        dispatch_log(disp, level, "shutting down due to TCP "
                                     "receive error: %s: %s", buf,
                                     isc_result_totext(tcpmsg->result));
                        do_cancel(disp);
                        break;
                }

                /*
                 * The event is statically allocated in the tcpmsg
                 * structure, and destroy_disp() frees the tcpmsg, so we must
                 * free the event *before* calling destroy_disp().
                 */
                isc_event_free(&ev_in);

                disp->shutting_down = 1;
                disp->shutdown_why = tcpmsg->result;

                /*
                 * If the recv() was canceled pass the word on.
                 */
                killit = destroy_disp_ok(disp);
                UNLOCK(&disp->lock);
                if (killit)
                        isc_task_send(disp->task[0], &disp->ctlevent);
                return;
        }

        dispatch_log(disp, LVL(90), "result %d, length == %d, addr = %p",
                     tcpmsg->result,
                     tcpmsg->buffer.length, tcpmsg->buffer.base);

        /*
         * Peek into the buffer to see what we can see.
         */
        dres = dns_message_peekheader(&tcpmsg->buffer, &id, &flags);
        if (dres != ISC_R_SUCCESS) {
                dispatch_log(disp, LVL(10), "got garbage packet");
                goto restart;
        }

        dispatch_log(disp, LVL(92),
                     "got valid DNS message header, /QR %c, id %u",
                     ((flags & DNS_MESSAGEFLAG_QR) ? '1' : '0'), id);

        /*
         * Allocate an event to send to the query or response client, and
         * allocate a new buffer for our use.
         */

        /*
         * Look at flags.  If query, drop it. If response,
         * look to see where it goes.
         */
        if ((flags & DNS_MESSAGEFLAG_QR) == 0) {
                /*
                 * Query.
                 */
                goto restart;
        }

        /*
         * Response.
         */
        bucket = dns_hash(qid, &tcpmsg->address, id, disp->localport);
        LOCK(&qid->lock);
        resp = entry_search(qid, &tcpmsg->address, id, disp->localport, bucket);
        dispatch_log(disp, LVL(90),
                     "search for response in bucket %d: %s",
                     bucket, (resp == NULL ? "not found" : "found"));

        if (resp == NULL)
                goto unlock;
        queue_response = resp->item_out;
        rev = allocate_devent(disp);
        if (rev == NULL)
                goto unlock;

        /*
         * At this point, rev contains the event we want to fill in, and
         * resp contains the information on the place to send it to.
         * Send the event off.
         */
        dns_tcpmsg_keepbuffer(tcpmsg, &rev->buffer);
        disp->tcpbuffers++;
        rev->result = ISC_R_SUCCESS;
        rev->id = id;
        rev->addr = tcpmsg->address;
        if (queue_response) {
                ISC_LIST_APPEND(resp->items, rev, ev_link);
        } else {
                ISC_EVENT_INIT(rev, sizeof(*rev), 0, NULL, DNS_EVENT_DISPATCH,
                               resp->action, resp->arg, resp, NULL, NULL);
                request_log(disp, resp, LVL(90),
                            "[b] Sent event %p buffer %p len %d to task %p",
                            rev, rev->buffer.base, rev->buffer.length,
                            resp->task);
                resp->item_out = ISC_TRUE;
                isc_task_send(resp->task, ISC_EVENT_PTR(&rev));
        }
 unlock:
        UNLOCK(&qid->lock);

        /*
         * Restart recv() to get the next packet.
         */
 restart:
        (void)startrecv(disp, NULL);

        isc_event_free(&ev_in);
        UNLOCK(&disp->lock);
}

/*
 * disp must be locked.
 */
static isc_result_t
startrecv(dns_dispatch_t *disp, dispsocket_t *dispsock) {
        isc_result_t res;
        isc_region_t region;
        isc_socket_t *sock;

        if (disp->shutting_down == 1)
                return (ISC_R_SUCCESS);

        if ((disp->attributes & DNS_DISPATCHATTR_NOLISTEN) != 0)
                return (ISC_R_SUCCESS);

        if (disp->recv_pending != 0 && dispsock == NULL)
                return (ISC_R_SUCCESS);

        if (disp->mgr->buffers >= disp->mgr->maxbuffers)
                return (ISC_R_NOMEMORY);

        if ((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0 &&
            dispsock == NULL)
                return (ISC_R_SUCCESS);

        if (dispsock != NULL)
                sock = dispsock->socket;
        else
                sock = disp->socket;
        INSIST(sock != NULL);

        switch (disp->socktype) {
                /*
                 * UDP reads are always maximal.
                 */
        case isc_sockettype_udp:
                region.length = disp->mgr->buffersize;
                region.base = allocate_udp_buffer(disp);
                if (region.base == NULL)
                        return (ISC_R_NOMEMORY);
                if (dispsock != NULL) {
                        isc_task_t *dt = dispsock->task;
                        isc_socketevent_t *sev =
                                allocate_sevent(disp, sock,
                                                ISC_SOCKEVENT_RECVDONE,
                                                udp_exrecv, dispsock);
                        if (sev == NULL) {
                                free_buffer(disp, region.base, region.length);
                                return (ISC_R_NOMEMORY);
                        }

                        res = isc_socket_recv2(sock, &region, 1, dt, sev, 0);
                        if (res != ISC_R_SUCCESS) {
                                free_buffer(disp, region.base, region.length);
                                return (res);
                        }
                } else {
                        isc_task_t *dt = disp->task[0];
                        isc_socketevent_t *sev =
                                allocate_sevent(disp, sock,
                                                ISC_SOCKEVENT_RECVDONE,
                                                udp_shrecv, disp);
                        if (sev == NULL) {
                                free_buffer(disp, region.base, region.length);
                                return (ISC_R_NOMEMORY);
                        }

                        res = isc_socket_recv2(sock, &region, 1, dt, sev, 0);
                        if (res != ISC_R_SUCCESS) {
                                free_buffer(disp, region.base, region.length);
                                disp->shutdown_why = res;
                                disp->shutting_down = 1;
                                do_cancel(disp);
                                return (ISC_R_SUCCESS); /* recover by cancel */
                        }
                        INSIST(disp->recv_pending == 0);
                        disp->recv_pending = 1;
                }
                break;

        case isc_sockettype_tcp:
                res = dns_tcpmsg_readmessage(&disp->tcpmsg, disp->task[0],
                                             tcp_recv, disp);
                if (res != ISC_R_SUCCESS) {
                        disp->shutdown_why = res;
                        disp->shutting_down = 1;
                        do_cancel(disp);
                        return (ISC_R_SUCCESS); /* recover by cancel */
                }
                INSIST(disp->recv_pending == 0);
                disp->recv_pending = 1;
                break;
        default:
                INSIST(0);
                break;
        }

        return (ISC_R_SUCCESS);
}

/*
 * Mgr must be locked when calling this function.
 */
static isc_boolean_t
destroy_mgr_ok(dns_dispatchmgr_t *mgr) {
        mgr_log(mgr, LVL(90),
                "destroy_mgr_ok: shuttingdown=%d, listnonempty=%d, "
                "depool=%d, rpool=%d, dpool=%d",
                MGR_IS_SHUTTINGDOWN(mgr), !ISC_LIST_EMPTY(mgr->list),
                isc_mempool_getallocated(mgr->depool),
                isc_mempool_getallocated(mgr->rpool),
                isc_mempool_getallocated(mgr->dpool));
        if (!MGR_IS_SHUTTINGDOWN(mgr))
                return (ISC_FALSE);
        if (!ISC_LIST_EMPTY(mgr->list))
                return (ISC_FALSE);
        if (isc_mempool_getallocated(mgr->depool) != 0)
                return (ISC_FALSE);
        if (isc_mempool_getallocated(mgr->rpool) != 0)
                return (ISC_FALSE);
        if (isc_mempool_getallocated(mgr->dpool) != 0)
                return (ISC_FALSE);

        return (ISC_TRUE);
}

/*
 * Mgr must be unlocked when calling this function.
 */
static void
destroy_mgr(dns_dispatchmgr_t **mgrp) {
        isc_mem_t *mctx;
        dns_dispatchmgr_t *mgr;

        mgr = *mgrp;
        *mgrp = NULL;

        mctx = mgr->mctx;

        mgr->magic = 0;
        mgr->mctx = NULL;
        DESTROYLOCK(&mgr->lock);
        mgr->state = 0;

        if (mgr->rngctx != NULL)
                isc_rng_detach(&mgr->rngctx);
        DESTROYLOCK(&mgr->rng_lock);

        isc_mempool_destroy(&mgr->depool);
        isc_mempool_destroy(&mgr->rpool);
        isc_mempool_destroy(&mgr->dpool);
        if (mgr->bpool != NULL)
                isc_mempool_destroy(&mgr->bpool);
        if (mgr->spool != NULL)
                isc_mempool_destroy(&mgr->spool);

        DESTROYLOCK(&mgr->spool_lock);
        DESTROYLOCK(&mgr->bpool_lock);
        DESTROYLOCK(&mgr->dpool_lock);
        DESTROYLOCK(&mgr->rpool_lock);
        DESTROYLOCK(&mgr->depool_lock);

        if (mgr->entropy != NULL)
                isc_entropy_detach(&mgr->entropy);
        if (mgr->qid != NULL)
                qid_destroy(mctx, &mgr->qid);

        DESTROYLOCK(&mgr->buffer_lock);

        if (mgr->blackhole != NULL)
                dns_acl_detach(&mgr->blackhole);

        if (mgr->stats != NULL)
                isc_stats_detach(&mgr->stats);

        if (mgr->v4ports != NULL) {
                isc_mem_put(mctx, mgr->v4ports,
                            mgr->nv4ports * sizeof(in_port_t));
        }
        if (mgr->v6ports != NULL) {
                isc_mem_put(mctx, mgr->v6ports,
                            mgr->nv6ports * sizeof(in_port_t));
        }
        isc_mem_put(mctx, mgr, sizeof(dns_dispatchmgr_t));
        isc_mem_detach(&mctx);
}

static isc_result_t
open_socket(isc_socketmgr_t *mgr, isc_sockaddr_t *local,
            unsigned int options, isc_socket_t **sockp,
            isc_socket_t *dup_socket)
{
        isc_socket_t *sock;
        isc_result_t result;

        sock = *sockp;
        if (sock != NULL) {
                result = isc_socket_open(sock);
                if (result != ISC_R_SUCCESS)
                        return (result);
        } else if (dup_socket != NULL) {
                result = isc_socket_dup(dup_socket, &sock);
                if (result != ISC_R_SUCCESS)
                        return (result);

                isc_socket_setname(sock, "dispatcher", NULL);
                *sockp = sock;
                return (ISC_R_SUCCESS);
        } else {
                result = isc_socket_create(mgr, isc_sockaddr_pf(local),
                                        isc_sockettype_udp, &sock);
                if (result != ISC_R_SUCCESS)
                        return (result);
        }

        isc_socket_setname(sock, "dispatcher", NULL);

#ifndef ISC_ALLOW_MAPPED
        isc_socket_ipv6only(sock, ISC_TRUE);
#endif
        result = isc_socket_bind(sock, local, options);
        if (result != ISC_R_SUCCESS) {
                if (*sockp == NULL)
                        isc_socket_detach(&sock);
                else {
                        isc_socket_close(sock);
                }
                return (result);
        }

        *sockp = sock;
        return (ISC_R_SUCCESS);
}

/*%
 * Create a temporary port list to set the initial default set of dispatch
 * ports: [1024, 65535].  This is almost meaningless as the application will
 * normally set the ports explicitly, but is provided to fill some minor corner
 * cases.
 */
static isc_result_t
create_default_portset(isc_mem_t *mctx, isc_portset_t **portsetp) {
        isc_result_t result;

        result = isc_portset_create(mctx, portsetp);
        if (result != ISC_R_SUCCESS)
                return (result);
        isc_portset_addrange(*portsetp, 1024, 65535);

        return (ISC_R_SUCCESS);
}

/*
 * Publics.
 */

isc_result_t
dns_dispatchmgr_create(isc_mem_t *mctx, isc_entropy_t *entropy,
                       dns_dispatchmgr_t **mgrp)
{
        dns_dispatchmgr_t *mgr;
        isc_result_t result;
        isc_portset_t *v4portset = NULL;
        isc_portset_t *v6portset = NULL;

        REQUIRE(mctx != NULL);
        REQUIRE(mgrp != NULL && *mgrp == NULL);

        mgr = isc_mem_get(mctx, sizeof(dns_dispatchmgr_t));
        if (mgr == NULL)
                return (ISC_R_NOMEMORY);

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

        mgr->blackhole = NULL;
        mgr->stats = NULL;
        mgr->rngctx = NULL;

        result = isc_mutex_init(&mgr->lock);
        if (result != ISC_R_SUCCESS)
                goto deallocate;

        result = isc_mutex_init(&mgr->rng_lock);
        if (result != ISC_R_SUCCESS)
                goto kill_lock;

        result = isc_mutex_init(&mgr->buffer_lock);
        if (result != ISC_R_SUCCESS)
                goto kill_rng_lock;

        result = isc_mutex_init(&mgr->depool_lock);
        if (result != ISC_R_SUCCESS)
                goto kill_buffer_lock;

        result = isc_mutex_init(&mgr->rpool_lock);
        if (result != ISC_R_SUCCESS)
                goto kill_depool_lock;

        result = isc_mutex_init(&mgr->dpool_lock);
        if (result != ISC_R_SUCCESS)
                goto kill_rpool_lock;

        result = isc_mutex_init(&mgr->bpool_lock);
        if (result != ISC_R_SUCCESS)
                goto kill_dpool_lock;

        result = isc_mutex_init(&mgr->spool_lock);
        if (result != ISC_R_SUCCESS)
                goto kill_bpool_lock;

        mgr->depool = NULL;
        if (isc_mempool_create(mgr->mctx, sizeof(dns_dispatchevent_t),
                               &mgr->depool) != ISC_R_SUCCESS) {
                result = ISC_R_NOMEMORY;
                goto kill_spool_lock;
        }

        mgr->rpool = NULL;
        if (isc_mempool_create(mgr->mctx, sizeof(dns_dispentry_t),
                               &mgr->rpool) != ISC_R_SUCCESS) {
                result = ISC_R_NOMEMORY;
                goto kill_depool;
        }

        mgr->dpool = NULL;
        if (isc_mempool_create(mgr->mctx, sizeof(dns_dispatch_t),
                               &mgr->dpool) != ISC_R_SUCCESS) {
                result = ISC_R_NOMEMORY;
                goto kill_rpool;
        }

        isc_mempool_setname(mgr->depool, "dispmgr_depool");
        isc_mempool_setmaxalloc(mgr->depool, 32768);
        isc_mempool_setfreemax(mgr->depool, 32768);
        isc_mempool_associatelock(mgr->depool, &mgr->depool_lock);
        isc_mempool_setfillcount(mgr->depool, 32);

        isc_mempool_setname(mgr->rpool, "dispmgr_rpool");
        isc_mempool_setmaxalloc(mgr->rpool, 32768);
        isc_mempool_setfreemax(mgr->rpool, 32768);
        isc_mempool_associatelock(mgr->rpool, &mgr->rpool_lock);
        isc_mempool_setfillcount(mgr->rpool, 32);

        isc_mempool_setname(mgr->dpool, "dispmgr_dpool");
        isc_mempool_setmaxalloc(mgr->dpool, 32768);
        isc_mempool_setfreemax(mgr->dpool, 32768);
        isc_mempool_associatelock(mgr->dpool, &mgr->dpool_lock);
        isc_mempool_setfillcount(mgr->dpool, 32);

        mgr->buffers = 0;
        mgr->buffersize = 0;
        mgr->maxbuffers = 0;
        mgr->bpool = NULL;
        mgr->spool = NULL;
        mgr->entropy = NULL;
        mgr->qid = NULL;
        mgr->state = 0;
        ISC_LIST_INIT(mgr->list);
        mgr->v4ports = NULL;
        mgr->v6ports = NULL;
        mgr->nv4ports = 0;
        mgr->nv6ports = 0;
        mgr->magic = DNS_DISPATCHMGR_MAGIC;

        result = create_default_portset(mctx, &v4portset);
        if (result == ISC_R_SUCCESS) {
                result = create_default_portset(mctx, &v6portset);
                if (result == ISC_R_SUCCESS) {
                        result = dns_dispatchmgr_setavailports(mgr,
                                                               v4portset,
                                                               v6portset);
                }
        }
        if (v4portset != NULL)
                isc_portset_destroy(mctx, &v4portset);
        if (v6portset != NULL)
                isc_portset_destroy(mctx, &v6portset);
        if (result != ISC_R_SUCCESS)
                goto kill_dpool;

        if (entropy != NULL)
                isc_entropy_attach(entropy, &mgr->entropy);

        result = isc_rng_create(mctx, mgr->entropy, &mgr->rngctx);
        if (result != ISC_R_SUCCESS)
                goto kill_dpool;

        *mgrp = mgr;
        return (ISC_R_SUCCESS);

 kill_dpool:
        isc_mempool_destroy(&mgr->dpool);
 kill_rpool:
        isc_mempool_destroy(&mgr->rpool);
 kill_depool:
        isc_mempool_destroy(&mgr->depool);
 kill_spool_lock:
        DESTROYLOCK(&mgr->spool_lock);
 kill_bpool_lock:
        DESTROYLOCK(&mgr->bpool_lock);
 kill_dpool_lock:
        DESTROYLOCK(&mgr->dpool_lock);
 kill_rpool_lock:
        DESTROYLOCK(&mgr->rpool_lock);
 kill_depool_lock:
        DESTROYLOCK(&mgr->depool_lock);
 kill_buffer_lock:
        DESTROYLOCK(&mgr->buffer_lock);
 kill_rng_lock:
        DESTROYLOCK(&mgr->rng_lock);
 kill_lock:
        DESTROYLOCK(&mgr->lock);
 deallocate:
        isc_mem_put(mctx, mgr, sizeof(dns_dispatchmgr_t));
        isc_mem_detach(&mctx);

        return (result);
}

void
dns_dispatchmgr_setblackhole(dns_dispatchmgr_t *mgr, dns_acl_t *blackhole) {
        REQUIRE(VALID_DISPATCHMGR(mgr));
        if (mgr->blackhole != NULL)
                dns_acl_detach(&mgr->blackhole);
        dns_acl_attach(blackhole, &mgr->blackhole);
}

dns_acl_t *
dns_dispatchmgr_getblackhole(dns_dispatchmgr_t *mgr) {
        REQUIRE(VALID_DISPATCHMGR(mgr));
        return (mgr->blackhole);
}

void
dns_dispatchmgr_setblackportlist(dns_dispatchmgr_t *mgr,
                                 dns_portlist_t *portlist)
{
        REQUIRE(VALID_DISPATCHMGR(mgr));
        UNUSED(portlist);

        /* This function is deprecated: use dns_dispatchmgr_setavailports(). */
        return;
}

dns_portlist_t *
dns_dispatchmgr_getblackportlist(dns_dispatchmgr_t *mgr) {
        REQUIRE(VALID_DISPATCHMGR(mgr));
        return (NULL);          /* this function is deprecated */
}

isc_result_t
dns_dispatchmgr_setavailports(dns_dispatchmgr_t *mgr, isc_portset_t *v4portset,
                              isc_portset_t *v6portset)
{
        in_port_t *v4ports, *v6ports, p;
        unsigned int nv4ports, nv6ports, i4, i6;

        REQUIRE(VALID_DISPATCHMGR(mgr));

        nv4ports = isc_portset_nports(v4portset);
        nv6ports = isc_portset_nports(v6portset);

        v4ports = NULL;
        if (nv4ports != 0) {
                v4ports = isc_mem_get(mgr->mctx, sizeof(in_port_t) * nv4ports);
                if (v4ports == NULL)
                        return (ISC_R_NOMEMORY);
        }
        v6ports = NULL;
        if (nv6ports != 0) {
                v6ports = isc_mem_get(mgr->mctx, sizeof(in_port_t) * nv6ports);
                if (v6ports == NULL) {
                        if (v4ports != NULL) {
                                isc_mem_put(mgr->mctx, v4ports,
                                            sizeof(in_port_t) *
                                            isc_portset_nports(v4portset));
                        }
                        return (ISC_R_NOMEMORY);
                }
        }

        p = 0;
        i4 = 0;
        i6 = 0;
        do {
                if (isc_portset_isset(v4portset, p)) {
                        INSIST(i4 < nv4ports);
                        v4ports[i4++] = p;
                }
                if (isc_portset_isset(v6portset, p)) {
                        INSIST(i6 < nv6ports);
                        v6ports[i6++] = p;
                }
        } while (p++ < 65535);
        INSIST(i4 == nv4ports && i6 == nv6ports);

        PORTBUFLOCK(mgr);
        if (mgr->v4ports != NULL) {
                isc_mem_put(mgr->mctx, mgr->v4ports,
                            mgr->nv4ports * sizeof(in_port_t));
        }
        mgr->v4ports = v4ports;
        mgr->nv4ports = nv4ports;

        if (mgr->v6ports != NULL) {
                isc_mem_put(mgr->mctx, mgr->v6ports,
                            mgr->nv6ports * sizeof(in_port_t));
        }
        mgr->v6ports = v6ports;
        mgr->nv6ports = nv6ports;
        PORTBUFUNLOCK(mgr);

        return (ISC_R_SUCCESS);
}

static isc_result_t
dns_dispatchmgr_setudp(dns_dispatchmgr_t *mgr,
                       unsigned int buffersize, unsigned int maxbuffers,
                       unsigned int maxrequests, unsigned int buckets,
                       unsigned int increment)
{
        isc_result_t result;

        REQUIRE(VALID_DISPATCHMGR(mgr));
        REQUIRE(buffersize >= 512 && buffersize < (64 * 1024));
        REQUIRE(maxbuffers > 0);
        REQUIRE(buckets < 2097169);  /* next prime > 65536 * 32 */
        REQUIRE(increment > buckets);

        /*
         * Keep some number of items around.  This should be a config
         * option.  For now, keep 8, but later keep at least two even
         * if the caller wants less.  This allows us to ensure certain
         * things, like an event can be "freed" and the next allocation
         * will always succeed.
         *
         * Note that if limits are placed on anything here, we use one
         * event internally, so the actual limit should be "wanted + 1."
         *
         * XXXMLG
         */

        if (maxbuffers < 8)
                maxbuffers = 8;

        LOCK(&mgr->buffer_lock);

        /* Create or adjust buffer pool */
        if (mgr->bpool != NULL) {
                /*
                 * We only increase the maxbuffers to avoid accidental buffer
                 * shortage.  Ideally we'd separate the manager-wide maximum
                 * from per-dispatch limits and respect the latter within the
                 * global limit.  But at this moment that's deemed to be
                 * overkilling and isn't worth additional implementation
                 * complexity.
                 */
                if (maxbuffers > mgr->maxbuffers) {
                        isc_mempool_setmaxalloc(mgr->bpool, maxbuffers);
                        isc_mempool_setfreemax(mgr->bpool, maxbuffers);
                        mgr->maxbuffers = maxbuffers;
                }
        } else {
                result = isc_mempool_create(mgr->mctx, buffersize, &mgr->bpool);
                if (result != ISC_R_SUCCESS) {
                        UNLOCK(&mgr->buffer_lock);
                        return (result);
                }
                isc_mempool_setname(mgr->bpool, "dispmgr_bpool");
                isc_mempool_setmaxalloc(mgr->bpool, maxbuffers);
                isc_mempool_setfreemax(mgr->bpool, maxbuffers);
                isc_mempool_associatelock(mgr->bpool, &mgr->bpool_lock);
                isc_mempool_setfillcount(mgr->bpool, 32);
        }

        /* Create or adjust socket pool */
        if (mgr->spool != NULL) {
                if (maxrequests < DNS_DISPATCH_POOLSOCKS * 2) {
                        isc_mempool_setmaxalloc(mgr->spool,
                                                DNS_DISPATCH_POOLSOCKS * 2);
                        isc_mempool_setfreemax(mgr->spool,
                                               DNS_DISPATCH_POOLSOCKS * 2);
                }
                UNLOCK(&mgr->buffer_lock);
                return (ISC_R_SUCCESS);
        }
        result = isc_mempool_create(mgr->mctx, sizeof(dispsocket_t),
                                    &mgr->spool);
        if (result != ISC_R_SUCCESS) {
                UNLOCK(&mgr->buffer_lock);
                goto cleanup;
        }
        isc_mempool_setname(mgr->spool, "dispmgr_spool");
        isc_mempool_setmaxalloc(mgr->spool, maxrequests);
        isc_mempool_setfreemax(mgr->spool, maxrequests);
        isc_mempool_associatelock(mgr->spool, &mgr->spool_lock);
        isc_mempool_setfillcount(mgr->spool, 32);

        result = qid_allocate(mgr, buckets, increment, &mgr->qid, ISC_TRUE);
        if (result != ISC_R_SUCCESS)
                goto cleanup;

        mgr->buffersize = buffersize;
        mgr->maxbuffers = maxbuffers;
        UNLOCK(&mgr->buffer_lock);
        return (ISC_R_SUCCESS);

 cleanup:
        isc_mempool_destroy(&mgr->bpool);
        if (mgr->spool != NULL)
                isc_mempool_destroy(&mgr->spool);
        UNLOCK(&mgr->buffer_lock);
        return (result);
}

void
dns_dispatchmgr_destroy(dns_dispatchmgr_t **mgrp) {
        dns_dispatchmgr_t *mgr;
        isc_boolean_t killit;

        REQUIRE(mgrp != NULL);
        REQUIRE(VALID_DISPATCHMGR(*mgrp));

        mgr = *mgrp;
        *mgrp = NULL;

        LOCK(&mgr->lock);
        mgr->state |= MGR_SHUTTINGDOWN;
        killit = destroy_mgr_ok(mgr);
        UNLOCK(&mgr->lock);

        mgr_log(mgr, LVL(90), "destroy: killit=%d", killit);

        if (killit)
                destroy_mgr(&mgr);
}

void
dns_dispatchmgr_setstats(dns_dispatchmgr_t *mgr, isc_stats_t *stats) {
        REQUIRE(VALID_DISPATCHMGR(mgr));
        REQUIRE(ISC_LIST_EMPTY(mgr->list));
        REQUIRE(mgr->stats == NULL);

        isc_stats_attach(stats, &mgr->stats);
}

static int
port_cmp(const void *key, const void *ent) {
        in_port_t p1 = *(const in_port_t *)key;
        in_port_t p2 = *(const in_port_t *)ent;

        if (p1 < p2)
                return (-1);
        else if (p1 == p2)
                return (0);
        else
                return (1);
}

static isc_boolean_t
portavailable(dns_dispatchmgr_t *mgr, isc_socket_t *sock,
              isc_sockaddr_t *sockaddrp)
{
        isc_sockaddr_t sockaddr;
        isc_result_t result;
        in_port_t *ports, port;
        unsigned int nports;
        isc_boolean_t available = ISC_FALSE;

        REQUIRE(sock != NULL || sockaddrp != NULL);

        PORTBUFLOCK(mgr);
        if (sock != NULL) {
                sockaddrp = &sockaddr;
                result = isc_socket_getsockname(sock, sockaddrp);
                if (result != ISC_R_SUCCESS)
                        goto unlock;
        }

        if (isc_sockaddr_pf(sockaddrp) == AF_INET) {
                ports = mgr->v4ports;
                nports = mgr->nv4ports;
        } else {
                ports = mgr->v6ports;
                nports = mgr->nv6ports;
        }
        if (ports == NULL)
                goto unlock;

        port = isc_sockaddr_getport(sockaddrp);
        if (bsearch(&port, ports, nports, sizeof(in_port_t), port_cmp) != NULL)
                available = ISC_TRUE;

unlock:
        PORTBUFUNLOCK(mgr);
        return (available);
}

#define ATTRMATCH(_a1, _a2, _mask) (((_a1) & (_mask)) == ((_a2) & (_mask)))

static isc_boolean_t
local_addr_match(dns_dispatch_t *disp, isc_sockaddr_t *addr) {
        isc_sockaddr_t sockaddr;
        isc_result_t result;

        REQUIRE(disp->socket != NULL);

        if (addr == NULL)
                return (ISC_TRUE);

        /*
         * Don't match wildcard ports unless the port is available in the
         * current configuration.
         */
        if (isc_sockaddr_getport(addr) == 0 &&
            isc_sockaddr_getport(&disp->local) == 0 &&
            !portavailable(disp->mgr, disp->socket, NULL)) {
                return (ISC_FALSE);
        }

        /*
         * Check if we match the binding <address,port>.
         * Wildcard ports match/fail here.
         */
        if (isc_sockaddr_equal(&disp->local, addr))
                return (ISC_TRUE);
        if (isc_sockaddr_getport(addr) == 0)
                return (ISC_FALSE);

        /*
         * Check if we match a bound wildcard port <address,port>.
         */
        if (!isc_sockaddr_eqaddr(&disp->local, addr))
                return (ISC_FALSE);
        result = isc_socket_getsockname(disp->socket, &sockaddr);
        if (result != ISC_R_SUCCESS)
                return (ISC_FALSE);

        return (isc_sockaddr_equal(&sockaddr, addr));
}

/*
 * Requires mgr be locked.
 *
 * No dispatcher can be locked by this thread when calling this function.
 *
 *
 * NOTE:
 *      If a matching dispatcher is found, it is locked after this function
 *      returns, and must be unlocked by the caller.
 */
static isc_result_t
dispatch_find(dns_dispatchmgr_t *mgr, isc_sockaddr_t *local,
              unsigned int attributes, unsigned int mask,
              dns_dispatch_t **dispp)
{
        dns_dispatch_t *disp;
        isc_result_t result;

        /*
         * Make certain that we will not match a private or exclusive dispatch.
         */
        attributes &= ~(DNS_DISPATCHATTR_PRIVATE|DNS_DISPATCHATTR_EXCLUSIVE);
        mask |= (DNS_DISPATCHATTR_PRIVATE|DNS_DISPATCHATTR_EXCLUSIVE);

        disp = ISC_LIST_HEAD(mgr->list);
        while (disp != NULL) {
                LOCK(&disp->lock);
                if ((disp->shutting_down == 0)
                    && ATTRMATCH(disp->attributes, attributes, mask)
                    && local_addr_match(disp, local))
                        break;
                UNLOCK(&disp->lock);
                disp = ISC_LIST_NEXT(disp, link);
        }

        if (disp == NULL) {
                result = ISC_R_NOTFOUND;
                goto out;
        }

        *dispp = disp;
        result = ISC_R_SUCCESS;
 out:

        return (result);
}

static isc_result_t
qid_allocate(dns_dispatchmgr_t *mgr, unsigned int buckets,
             unsigned int increment, dns_qid_t **qidp,
             isc_boolean_t needsocktable)
{
        dns_qid_t *qid;
        unsigned int i;
        isc_result_t result;

        REQUIRE(VALID_DISPATCHMGR(mgr));
        REQUIRE(buckets < 2097169);  /* next prime > 65536 * 32 */
        REQUIRE(increment > buckets);
        REQUIRE(qidp != NULL && *qidp == NULL);

        qid = isc_mem_get(mgr->mctx, sizeof(*qid));
        if (qid == NULL)
                return (ISC_R_NOMEMORY);

        qid->qid_table = isc_mem_get(mgr->mctx,
                                     buckets * sizeof(dns_displist_t));
        if (qid->qid_table == NULL) {
                isc_mem_put(mgr->mctx, qid, sizeof(*qid));
                return (ISC_R_NOMEMORY);
        }

        qid->sock_table = NULL;
        if (needsocktable) {
                qid->sock_table = isc_mem_get(mgr->mctx, buckets *
                                              sizeof(dispsocketlist_t));
                if (qid->sock_table == NULL) {
                        isc_mem_put(mgr->mctx, qid->qid_table,
                                    buckets * sizeof(dns_displist_t));
                        isc_mem_put(mgr->mctx, qid, sizeof(*qid));
                        return (ISC_R_NOMEMORY);
                }
        }

        result = isc_mutex_init(&qid->lock);
        if (result != ISC_R_SUCCESS) {
                if (qid->sock_table != NULL) {
                        isc_mem_put(mgr->mctx, qid->sock_table,
                                    buckets * sizeof(dispsocketlist_t));
                }
                isc_mem_put(mgr->mctx, qid->qid_table,
                            buckets * sizeof(dns_displist_t));
                isc_mem_put(mgr->mctx, qid, sizeof(*qid));
                return (result);
        }

        for (i = 0; i < buckets; i++) {
                ISC_LIST_INIT(qid->qid_table[i]);
                if (qid->sock_table != NULL)
                        ISC_LIST_INIT(qid->sock_table[i]);
        }

        qid->qid_nbuckets = buckets;
        qid->qid_increment = increment;
        qid->magic = QID_MAGIC;
        *qidp = qid;
        return (ISC_R_SUCCESS);
}

static void
qid_destroy(isc_mem_t *mctx, dns_qid_t **qidp) {
        dns_qid_t *qid;

        REQUIRE(qidp != NULL);
        qid = *qidp;

        REQUIRE(VALID_QID(qid));

        *qidp = NULL;
        qid->magic = 0;
        isc_mem_put(mctx, qid->qid_table,
                    qid->qid_nbuckets * sizeof(dns_displist_t));
        if (qid->sock_table != NULL) {
                isc_mem_put(mctx, qid->sock_table,
                            qid->qid_nbuckets * sizeof(dispsocketlist_t));
        }
        DESTROYLOCK(&qid->lock);
        isc_mem_put(mctx, qid, sizeof(*qid));
}

/*
 * Allocate and set important limits.
 */
static isc_result_t
dispatch_allocate(dns_dispatchmgr_t *mgr, unsigned int maxrequests,
                  dns_dispatch_t **dispp)
{
        dns_dispatch_t *disp;
        isc_result_t result;

        REQUIRE(VALID_DISPATCHMGR(mgr));
        REQUIRE(dispp != NULL && *dispp == NULL);

        /*
         * Set up the dispatcher, mostly.  Don't bother setting some of
         * the options that are controlled by tcp vs. udp, etc.
         */

        disp = isc_mempool_get(mgr->dpool);
        if (disp == NULL)
                return (ISC_R_NOMEMORY);

        disp->magic = 0;
        disp->mgr = mgr;
        disp->maxrequests = maxrequests;
        disp->attributes = 0;
        ISC_LINK_INIT(disp, link);
        disp->refcount = 1;
        disp->recv_pending = 0;
        memset(&disp->local, 0, sizeof(disp->local));
        memset(&disp->peer, 0, sizeof(disp->peer));
        disp->localport = 0;
        disp->shutting_down = 0;
        disp->shutdown_out = 0;
        disp->connected = 0;
        disp->tcpmsg_valid = 0;
        disp->shutdown_why = ISC_R_UNEXPECTED;
        disp->requests = 0;
        disp->tcpbuffers = 0;
        disp->qid = NULL;
        ISC_LIST_INIT(disp->activesockets);
        ISC_LIST_INIT(disp->inactivesockets);
        disp->nsockets = 0;
        disp->rngctx = NULL;
        isc_rng_attach(mgr->rngctx, &disp->rngctx);
        disp->port_table = NULL;
        disp->portpool = NULL;
        disp->dscp = -1;

        result = isc_mutex_init(&disp->lock);
        if (result != ISC_R_SUCCESS)
                goto deallocate;

        disp->failsafe_ev = allocate_devent(disp);
        if (disp->failsafe_ev == NULL) {
                result = ISC_R_NOMEMORY;
                goto kill_lock;
        }

        disp->magic = DISPATCH_MAGIC;

        *dispp = disp;
        return (ISC_R_SUCCESS);

        /*
         * error returns
         */
 kill_lock:
        DESTROYLOCK(&disp->lock);
 deallocate:
        if (disp->rngctx != NULL)
                isc_rng_detach(&disp->rngctx);
        isc_mempool_put(mgr->dpool, disp);

        return (result);
}


/*
 * MUST be unlocked, and not used by anything.
 */
static void
dispatch_free(dns_dispatch_t **dispp) {
        dns_dispatch_t *disp;
        dns_dispatchmgr_t *mgr;
        int i;

        REQUIRE(VALID_DISPATCH(*dispp));
        disp = *dispp;
        *dispp = NULL;

        mgr = disp->mgr;
        REQUIRE(VALID_DISPATCHMGR(mgr));

        if (disp->tcpmsg_valid) {
                dns_tcpmsg_invalidate(&disp->tcpmsg);
                disp->tcpmsg_valid = 0;
        }

        INSIST(disp->tcpbuffers == 0);
        INSIST(disp->requests == 0);
        INSIST(disp->recv_pending == 0);
        INSIST(ISC_LIST_EMPTY(disp->activesockets));
        INSIST(ISC_LIST_EMPTY(disp->inactivesockets));

        isc_mempool_put(mgr->depool, disp->failsafe_ev);
        disp->failsafe_ev = NULL;

        if (disp->qid != NULL)
                qid_destroy(mgr->mctx, &disp->qid);

        if (disp->port_table != NULL) {
                for (i = 0; i < DNS_DISPATCH_PORTTABLESIZE; i++)
                        INSIST(ISC_LIST_EMPTY(disp->port_table[i]));
                isc_mem_put(mgr->mctx, disp->port_table,
                            sizeof(disp->port_table[0]) *
                            DNS_DISPATCH_PORTTABLESIZE);
        }

        if (disp->portpool != NULL)
                isc_mempool_destroy(&disp->portpool);

        if (disp->rngctx != NULL)
                isc_rng_detach(&disp->rngctx);

        disp->mgr = NULL;
        DESTROYLOCK(&disp->lock);
        disp->magic = 0;
        isc_mempool_put(mgr->dpool, disp);
}

isc_result_t
dns_dispatch_createtcp(dns_dispatchmgr_t *mgr, isc_socket_t *sock,
                       isc_taskmgr_t *taskmgr, unsigned int buffersize,
                       unsigned int maxbuffers, unsigned int maxrequests,
                       unsigned int buckets, unsigned int increment,
                       unsigned int attributes, dns_dispatch_t **dispp)
{

        attributes |= DNS_DISPATCHATTR_PRIVATE;  /* XXXMLG */

        return (dns_dispatch_createtcp2(mgr, sock, taskmgr, NULL, NULL,
                                        buffersize, maxbuffers, maxrequests,
                                        buckets, increment, attributes,
                                        dispp));
}

isc_result_t
dns_dispatch_createtcp2(dns_dispatchmgr_t *mgr, isc_socket_t *sock,
                        isc_taskmgr_t *taskmgr, isc_sockaddr_t *localaddr,
                        isc_sockaddr_t *destaddr, unsigned int buffersize,
                        unsigned int maxbuffers, unsigned int maxrequests,
                        unsigned int buckets, unsigned int increment,
                        unsigned int attributes, dns_dispatch_t **dispp)
{
        isc_result_t result;
        dns_dispatch_t *disp;

        UNUSED(maxbuffers);
        UNUSED(buffersize);

        REQUIRE(VALID_DISPATCHMGR(mgr));
        REQUIRE(isc_socket_gettype(sock) == isc_sockettype_tcp);
        REQUIRE((attributes & DNS_DISPATCHATTR_TCP) != 0);
        REQUIRE((attributes & DNS_DISPATCHATTR_UDP) == 0);

        if (destaddr == NULL)
                attributes |= DNS_DISPATCHATTR_PRIVATE;  /* XXXMLG */

        LOCK(&mgr->lock);

        /*
         * dispatch_allocate() checks mgr for us.
         * qid_allocate() checks buckets and increment for us.
         */
        disp = NULL;
        result = dispatch_allocate(mgr, maxrequests, &disp);
        if (result != ISC_R_SUCCESS) {
                UNLOCK(&mgr->lock);
                return (result);
        }

        result = qid_allocate(mgr, buckets, increment, &disp->qid, ISC_FALSE);
        if (result != ISC_R_SUCCESS)
                goto deallocate_dispatch;

        disp->socktype = isc_sockettype_tcp;
        disp->socket = NULL;
        isc_socket_attach(sock, &disp->socket);

        disp->sepool = NULL;

        disp->ntasks = 1;
        disp->task[0] = NULL;
        result = isc_task_create(taskmgr, 0, &disp->task[0]);
        if (result != ISC_R_SUCCESS)
                goto kill_socket;

        disp->ctlevent = isc_event_allocate(mgr->mctx, disp,
                                            DNS_EVENT_DISPATCHCONTROL,
                                            destroy_disp, disp,
                                            sizeof(isc_event_t));
        if (disp->ctlevent == NULL) {
                result = ISC_R_NOMEMORY;
                goto kill_task;
        }

        isc_task_setname(disp->task[0], "tcpdispatch", disp);

        dns_tcpmsg_init(mgr->mctx, disp->socket, &disp->tcpmsg);
        disp->tcpmsg_valid = 1;

        disp->attributes = attributes;

        if (localaddr == NULL) {
                if (destaddr != NULL) {
                        switch (isc_sockaddr_pf(destaddr)) {
                        case AF_INET:
                                isc_sockaddr_any(&disp->local);
                                break;
                        case AF_INET6:
                                isc_sockaddr_any6(&disp->local);
                                break;
                        }
                }
        } else
                disp->local = *localaddr;

        if (destaddr != NULL)
                disp->peer = *destaddr;

        /*
         * Append it to the dispatcher list.
         */
        ISC_LIST_APPEND(mgr->list, disp, link);
        UNLOCK(&mgr->lock);

        mgr_log(mgr, LVL(90), "created TCP dispatcher %p", disp);
        dispatch_log(disp, LVL(90), "created task %p", disp->task[0]);
        *dispp = disp;

        return (ISC_R_SUCCESS);

        /*
         * Error returns.
         */
 kill_task:
        isc_task_detach(&disp->task[0]);
 kill_socket:
        isc_socket_detach(&disp->socket);
 deallocate_dispatch:
        dispatch_free(&disp);

        UNLOCK(&mgr->lock);

        return (result);
}

isc_result_t
dns_dispatch_gettcp(dns_dispatchmgr_t *mgr, isc_sockaddr_t *destaddr,
                    isc_sockaddr_t *localaddr, dns_dispatch_t **dispp)
{
        dns_dispatch_t *disp;
        isc_result_t result;
        isc_sockaddr_t peeraddr;
        isc_sockaddr_t sockname;
        unsigned int attributes, mask;
        isc_boolean_t match = ISC_FALSE;

        REQUIRE(VALID_DISPATCHMGR(mgr));
        REQUIRE(destaddr != NULL);
        REQUIRE(dispp != NULL && *dispp == NULL);

        attributes = DNS_DISPATCHATTR_TCP | DNS_DISPATCHATTR_CONNECTED;
        mask = DNS_DISPATCHATTR_TCP | DNS_DISPATCHATTR_PRIVATE |
               DNS_DISPATCHATTR_EXCLUSIVE | DNS_DISPATCHATTR_CONNECTED;

        LOCK(&mgr->lock);
        disp = ISC_LIST_HEAD(mgr->list);
        while (disp != NULL && !match) {
                LOCK(&disp->lock);
                if ((disp->shutting_down == 0) &&
                    ATTRMATCH(disp->attributes, attributes, mask) &&
                    (localaddr == NULL ||
                     isc_sockaddr_eqaddr(localaddr, &disp->local))) {
                        result = isc_socket_getsockname(disp->socket,
                                                        &sockname);
                        if (result == ISC_R_SUCCESS)
                                result = isc_socket_getpeername(disp->socket,
                                                                &peeraddr);
                        if (result == ISC_R_SUCCESS &&
                            isc_sockaddr_equal(destaddr, &peeraddr) &&
                            (localaddr == NULL ||
                             isc_sockaddr_eqaddr(localaddr, &sockname))) {
                                /* attach */
                                disp->refcount++;
                                *dispp = disp;
                                match = ISC_TRUE;
                        }
                }
                UNLOCK(&disp->lock);
                disp = ISC_LIST_NEXT(disp, link);
        }
        UNLOCK(&mgr->lock);
        return (match ? ISC_R_SUCCESS : ISC_R_NOTFOUND);
}

isc_result_t
dns_dispatch_gettcp2(dns_dispatchmgr_t *mgr, isc_sockaddr_t *destaddr,
                     isc_sockaddr_t *localaddr, isc_boolean_t *connected,
                     dns_dispatch_t **dispp)
{
        dns_dispatch_t *disp;
        isc_result_t result;
        isc_sockaddr_t peeraddr;
        isc_sockaddr_t sockname;
        unsigned int attributes, mask;
        isc_boolean_t match = ISC_FALSE;

        REQUIRE(VALID_DISPATCHMGR(mgr));
        REQUIRE(destaddr != NULL);
        REQUIRE(dispp != NULL && *dispp == NULL);
        REQUIRE(connected != NULL);

        /* First pass (same as dns_dispatch_gettcp()) */
        attributes = DNS_DISPATCHATTR_TCP | DNS_DISPATCHATTR_CONNECTED;
        mask = DNS_DISPATCHATTR_TCP | DNS_DISPATCHATTR_PRIVATE |
               DNS_DISPATCHATTR_EXCLUSIVE | DNS_DISPATCHATTR_CONNECTED;

        LOCK(&mgr->lock);
        disp = ISC_LIST_HEAD(mgr->list);
        while (disp != NULL && !match) {
                LOCK(&disp->lock);
                if ((disp->shutting_down == 0) &&
                    ATTRMATCH(disp->attributes, attributes, mask) &&
                    (localaddr == NULL ||
                     isc_sockaddr_eqaddr(localaddr, &disp->local))) {
                        result = isc_socket_getsockname(disp->socket,
                                                        &sockname);
                        if (result == ISC_R_SUCCESS)
                                result = isc_socket_getpeername(disp->socket,
                                                                &peeraddr);
                        if (result == ISC_R_SUCCESS &&
                            isc_sockaddr_equal(destaddr, &peeraddr) &&
                            (localaddr == NULL ||
                             isc_sockaddr_eqaddr(localaddr, &sockname))) {
                                /* attach */
                                disp->refcount++;
                                *dispp = disp;
                                match = ISC_TRUE;
                                *connected = ISC_TRUE;
                        }
                }
                UNLOCK(&disp->lock);
                disp = ISC_LIST_NEXT(disp, link);
        }
        if (match) {
                UNLOCK(&mgr->lock);
                return (ISC_R_SUCCESS);
        }

        /* Second pass */
        attributes = DNS_DISPATCHATTR_TCP;

        disp = ISC_LIST_HEAD(mgr->list);
        while (disp != NULL && !match) {
                LOCK(&disp->lock);
                if ((disp->shutting_down == 0) &&
                    ATTRMATCH(disp->attributes, attributes, mask) &&
                    (localaddr == NULL ||
                     isc_sockaddr_eqaddr(localaddr, &disp->local)) &&
                    isc_sockaddr_equal(destaddr, &disp->peer)) {
                        /* attach */
                        disp->refcount++;
                        *dispp = disp;
                        match = ISC_TRUE;
                }
                UNLOCK(&disp->lock);
                disp = ISC_LIST_NEXT(disp, link);
        }
        UNLOCK(&mgr->lock);
        return (match ? ISC_R_SUCCESS : ISC_R_NOTFOUND);
}

isc_result_t
dns_dispatch_getudp_dup(dns_dispatchmgr_t *mgr, isc_socketmgr_t *sockmgr,
                    isc_taskmgr_t *taskmgr, isc_sockaddr_t *localaddr,
                    unsigned int buffersize,
                    unsigned int maxbuffers, unsigned int maxrequests,
                    unsigned int buckets, unsigned int increment,
                    unsigned int attributes, unsigned int mask,
                    dns_dispatch_t **dispp, dns_dispatch_t *dup_dispatch)
{
        isc_result_t result;
        dns_dispatch_t *disp = NULL;

        REQUIRE(VALID_DISPATCHMGR(mgr));
        REQUIRE(sockmgr != NULL);
        REQUIRE(localaddr != NULL);
        REQUIRE(taskmgr != NULL);
        REQUIRE(buffersize >= 512 && buffersize < (64 * 1024));
        REQUIRE(maxbuffers > 0);
        REQUIRE(buckets < 2097169);  /* next prime > 65536 * 32 */
        REQUIRE(increment > buckets);
        REQUIRE(dispp != NULL && *dispp == NULL);
        REQUIRE((attributes & DNS_DISPATCHATTR_TCP) == 0);

        result = dns_dispatchmgr_setudp(mgr, buffersize, maxbuffers,
                                        maxrequests, buckets, increment);
        if (result != ISC_R_SUCCESS)
                return (result);

        LOCK(&mgr->lock);

        if ((attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0) {
                REQUIRE(isc_sockaddr_getport(localaddr) == 0);
                goto createudp;
        }

        /*
         * See if we have a dispatcher that matches.
         */
        if (dup_dispatch == NULL) {
                result = dispatch_find(mgr, localaddr, attributes, mask, &disp);
                if (result == ISC_R_SUCCESS) {
                        disp->refcount++;

                        if (disp->maxrequests < maxrequests)
                                disp->maxrequests = maxrequests;

                        if ((disp->attributes & DNS_DISPATCHATTR_NOLISTEN) == 0
                            && (attributes & DNS_DISPATCHATTR_NOLISTEN) != 0)
                        {
                                disp->attributes |= DNS_DISPATCHATTR_NOLISTEN;
                                if (disp->recv_pending != 0)
                                        isc_socket_cancel(disp->socket,
                                                          disp->task[0],
                                                          ISC_SOCKCANCEL_RECV);
                        }

                        UNLOCK(&disp->lock);
                        UNLOCK(&mgr->lock);

                        *dispp = disp;

                        return (ISC_R_SUCCESS);
                }
        }

 createudp:
        /*
         * Nope, create one.
         */
        result = dispatch_createudp(mgr, sockmgr, taskmgr, localaddr,
                                    maxrequests, attributes, &disp,
                                    dup_dispatch == NULL
                                            ? NULL
                                            : dup_dispatch->socket);

        if (result != ISC_R_SUCCESS) {
                UNLOCK(&mgr->lock);
                return (result);
        }

        UNLOCK(&mgr->lock);
        *dispp = disp;

        return (ISC_R_SUCCESS);
}

isc_result_t
dns_dispatch_getudp(dns_dispatchmgr_t *mgr, isc_socketmgr_t *sockmgr,
                    isc_taskmgr_t *taskmgr, isc_sockaddr_t *localaddr,
                    unsigned int buffersize,
                    unsigned int maxbuffers, unsigned int maxrequests,
                    unsigned int buckets, unsigned int increment,
                    unsigned int attributes, unsigned int mask,
                    dns_dispatch_t **dispp)
{
        return (dns_dispatch_getudp_dup(mgr, sockmgr, taskmgr, localaddr,
                                        buffersize, maxbuffers, maxrequests,
                                        buckets, increment, attributes,
                                        mask, dispp, NULL));
}

/*
 * mgr should be locked.
 */

#ifndef DNS_DISPATCH_HELD
#define DNS_DISPATCH_HELD 20U
#endif

static isc_result_t
get_udpsocket(dns_dispatchmgr_t *mgr, dns_dispatch_t *disp,
              isc_socketmgr_t *sockmgr, isc_sockaddr_t *localaddr,
              isc_socket_t **sockp, isc_socket_t *dup_socket)
{
        unsigned int i, j;
        isc_socket_t *held[DNS_DISPATCH_HELD];
        isc_sockaddr_t localaddr_bound;
        isc_socket_t *sock = NULL;
        isc_result_t result = ISC_R_SUCCESS;
        isc_boolean_t anyport;

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

        localaddr_bound = *localaddr;
        anyport = ISC_TF(isc_sockaddr_getport(localaddr) == 0);

        if (anyport) {
                unsigned int nports;
                in_port_t *ports;

                /*
                 * If no port is specified, we first try to pick up a random
                 * port by ourselves.
                 */
                if (isc_sockaddr_pf(localaddr) == AF_INET) {
                        nports = disp->mgr->nv4ports;
                        ports = disp->mgr->v4ports;
                } else {
                        nports = disp->mgr->nv6ports;
                        ports = disp->mgr->v6ports;
                }
                if (nports == 0)
                        return (ISC_R_ADDRNOTAVAIL);

                for (i = 0; i < 1024; i++) {
                        in_port_t prt;

                        prt = ports[isc_rng_uniformrandom(DISP_RNGCTX(disp),
                                                          nports)];
                        isc_sockaddr_setport(&localaddr_bound, prt);
                        result = open_socket(sockmgr, &localaddr_bound,
                                             0, &sock, NULL);
                        /*
                         * Continue if the port choosen is already in use
                         * or the OS has reserved it.
                         */
                        if (result == ISC_R_NOPERM ||
                            result == ISC_R_ADDRINUSE)
                                continue;
                        disp->localport = prt;
                        *sockp = sock;
                        return (result);
                }

                /*
                 * If this fails 1024 times, we then ask the kernel for
                 * choosing one.
                 */
        } else {
                /* Allow to reuse address for non-random ports. */
                result = open_socket(sockmgr, localaddr,
                                     ISC_SOCKET_REUSEADDRESS, &sock,
                                     dup_socket);

                if (result == ISC_R_SUCCESS)
                        *sockp = sock;

                return (result);
        }

        memset(held, 0, sizeof(held));
        i = 0;

        for (j = 0; j < 0xffffU; j++) {
                result = open_socket(sockmgr, localaddr, 0, &sock, NULL);
                if (result != ISC_R_SUCCESS)
                        goto end;
                else if (portavailable(mgr, sock, NULL))
                        break;
                if (held[i] != NULL)
                        isc_socket_detach(&held[i]);
                held[i++] = sock;
                sock = NULL;
                if (i == DNS_DISPATCH_HELD)
                        i = 0;
        }
        if (j == 0xffffU) {
                mgr_log(mgr, ISC_LOG_ERROR,
                        "avoid-v%s-udp-ports: unable to allocate "
                        "an available port",
                        isc_sockaddr_pf(localaddr) == AF_INET ? "4" : "6");
                result = ISC_R_FAILURE;
                goto end;
        }
        *sockp = sock;

end:
        for (i = 0; i < DNS_DISPATCH_HELD; i++) {
                if (held[i] != NULL)
                        isc_socket_detach(&held[i]);
        }

        return (result);
}

static isc_result_t
dispatch_createudp(dns_dispatchmgr_t *mgr, isc_socketmgr_t *sockmgr,
                   isc_taskmgr_t *taskmgr,
                   isc_sockaddr_t *localaddr,
                   unsigned int maxrequests,
                   unsigned int attributes,
                   dns_dispatch_t **dispp,
                   isc_socket_t *dup_socket)
{
        isc_result_t result;
        dns_dispatch_t *disp;
        isc_socket_t *sock = NULL;
        int i = 0;

        /*
         * dispatch_allocate() checks mgr for us.
         */
        disp = NULL;
        result = dispatch_allocate(mgr, maxrequests, &disp);
        if (result != ISC_R_SUCCESS)
                return (result);

        disp->socktype = isc_sockettype_udp;

        if ((attributes & DNS_DISPATCHATTR_EXCLUSIVE) == 0) {
                result = get_udpsocket(mgr, disp, sockmgr, localaddr, &sock,
                                       dup_socket);
                if (result != ISC_R_SUCCESS)
                        goto deallocate_dispatch;

                if (isc_log_wouldlog(dns_lctx, 90)) {
                        char addrbuf[ISC_SOCKADDR_FORMATSIZE];

                        isc_sockaddr_format(localaddr, addrbuf,
                                            ISC_SOCKADDR_FORMATSIZE);
                        mgr_log(mgr, LVL(90), "dns_dispatch_createudp: Created"
                                " UDP dispatch for %s with socket fd %d\n",
                                addrbuf, isc_socket_getfd(sock));
                }

        } else {
                isc_sockaddr_t sa_any;

                /*
                 * For dispatches using exclusive sockets with a specific
                 * source address, we only check if the specified address is
                 * available on the system.  Query sockets will be created later
                 * on demand.
                 */
                isc_sockaddr_anyofpf(&sa_any, isc_sockaddr_pf(localaddr));
                if (!isc_sockaddr_eqaddr(&sa_any, localaddr)) {
                        result = open_socket(sockmgr, localaddr, 0, &sock, NULL);
                        if (sock != NULL)
                                isc_socket_detach(&sock);
                        if (result != ISC_R_SUCCESS)
                                goto deallocate_dispatch;
                }

                disp->port_table = isc_mem_get(mgr->mctx,
                                               sizeof(disp->port_table[0]) *
                                               DNS_DISPATCH_PORTTABLESIZE);
                if (disp->port_table == NULL)
                        goto deallocate_dispatch;
                for (i = 0; i < DNS_DISPATCH_PORTTABLESIZE; i++)
                        ISC_LIST_INIT(disp->port_table[i]);

                result = isc_mempool_create(mgr->mctx, sizeof(dispportentry_t),
                                            &disp->portpool);
                if (result != ISC_R_SUCCESS)
                        goto deallocate_dispatch;
                isc_mempool_setname(disp->portpool, "disp_portpool");
                isc_mempool_setfreemax(disp->portpool, 128);
        }
        disp->socket = sock;
        disp->local = *localaddr;

        if ((attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0)
                disp->ntasks = MAX_INTERNAL_TASKS;
        else
                disp->ntasks = 1;
        for (i = 0; i < disp->ntasks; i++) {
                disp->task[i] = NULL;
                result = isc_task_create(taskmgr, 0, &disp->task[i]);
                if (result != ISC_R_SUCCESS) {
                        while (--i >= 0) {
                                isc_task_shutdown(disp->task[i]);
                                isc_task_detach(&disp->task[i]);
                        }
                        goto kill_socket;
                }
                isc_task_setname(disp->task[i], "udpdispatch", disp);
        }

        disp->ctlevent = isc_event_allocate(mgr->mctx, disp,
                                            DNS_EVENT_DISPATCHCONTROL,
                                            destroy_disp, disp,
                                            sizeof(isc_event_t));
        if (disp->ctlevent == NULL) {
                result = ISC_R_NOMEMORY;
                goto kill_task;
        }

        disp->sepool = NULL;
        if (isc_mempool_create(mgr->mctx, sizeof(isc_socketevent_t),
                               &disp->sepool) != ISC_R_SUCCESS)
        {
                result = ISC_R_NOMEMORY;
                goto kill_ctlevent;
        }

        result = isc_mutex_init(&disp->sepool_lock);
        if (result != ISC_R_SUCCESS)
                goto kill_sepool;

        isc_mempool_setname(disp->sepool, "disp_sepool");
        isc_mempool_setmaxalloc(disp->sepool, 32768);
        isc_mempool_setfreemax(disp->sepool, 32768);
        isc_mempool_associatelock(disp->sepool, &disp->sepool_lock);
        isc_mempool_setfillcount(disp->sepool, 16);

        attributes &= ~DNS_DISPATCHATTR_TCP;
        attributes |= DNS_DISPATCHATTR_UDP;
        disp->attributes = attributes;

        /*
         * Append it to the dispatcher list.
         */
        ISC_LIST_APPEND(mgr->list, disp, link);

        mgr_log(mgr, LVL(90), "created UDP dispatcher %p", disp);
        dispatch_log(disp, LVL(90), "created task %p", disp->task[0]); /* XXX */
        if (disp->socket != NULL)
                dispatch_log(disp, LVL(90), "created socket %p", disp->socket);

        *dispp = disp;

        return (result);

        /*
         * Error returns.
         */
 kill_sepool:
        isc_mempool_destroy(&disp->sepool);
 kill_ctlevent:
        isc_event_free(&disp->ctlevent);
 kill_task:
        for (i = 0; i < disp->ntasks; i++)
                isc_task_detach(&disp->task[i]);
 kill_socket:
        if (disp->socket != NULL)
                isc_socket_detach(&disp->socket);
 deallocate_dispatch:
        dispatch_free(&disp);

        return (result);
}

void
dns_dispatch_attach(dns_dispatch_t *disp, dns_dispatch_t **dispp) {
        REQUIRE(VALID_DISPATCH(disp));
        REQUIRE(dispp != NULL && *dispp == NULL);

        LOCK(&disp->lock);
        disp->refcount++;
        UNLOCK(&disp->lock);

        *dispp = disp;
}

/*
 * It is important to lock the manager while we are deleting the dispatch,
 * since dns_dispatch_getudp will call dispatch_find, which returns to
 * the caller a dispatch but does not attach to it until later.  _getudp
 * locks the manager, however, so locking it here will keep us from attaching
 * to a dispatcher that is in the process of going away.
 */
void
dns_dispatch_detach(dns_dispatch_t **dispp) {
        dns_dispatch_t *disp;
        dispsocket_t *dispsock;
        isc_boolean_t killit;

        REQUIRE(dispp != NULL && VALID_DISPATCH(*dispp));

        disp = *dispp;
        *dispp = NULL;

        LOCK(&disp->lock);

        INSIST(disp->refcount > 0);
        disp->refcount--;
        if (disp->refcount == 0) {
                if (disp->recv_pending > 0)
                        isc_socket_cancel(disp->socket, disp->task[0],
                                          ISC_SOCKCANCEL_RECV);
                for (dispsock = ISC_LIST_HEAD(disp->activesockets);
                     dispsock != NULL;
                     dispsock = ISC_LIST_NEXT(dispsock, link)) {
                        isc_socket_cancel(dispsock->socket, dispsock->task,
                                          ISC_SOCKCANCEL_RECV);
                }
                disp->shutting_down = 1;
        }

        dispatch_log(disp, LVL(90), "detach: refcount %d", disp->refcount);

        killit = destroy_disp_ok(disp);
        UNLOCK(&disp->lock);
        if (killit)
                isc_task_send(disp->task[0], &disp->ctlevent);
}

isc_result_t
dns_dispatch_addresponse2(dns_dispatch_t *disp, isc_sockaddr_t *dest,
                          isc_task_t *task, isc_taskaction_t action, void *arg,
                          dns_messageid_t *idp, dns_dispentry_t **resp,
                          isc_socketmgr_t *sockmgr)
{
        return (dns_dispatch_addresponse3(disp, 0, dest, task, action, arg,
                                          idp, resp, sockmgr));
}

isc_result_t
dns_dispatch_addresponse3(dns_dispatch_t *disp, unsigned int options,
                          isc_sockaddr_t *dest, isc_task_t *task,
                          isc_taskaction_t action, void *arg,
                          dns_messageid_t *idp, dns_dispentry_t **resp,
                          isc_socketmgr_t *sockmgr)
{
        dns_dispentry_t *res;
        unsigned int bucket;
        in_port_t localport = 0;
        dns_messageid_t id;
        int i;
        isc_boolean_t ok;
        dns_qid_t *qid;
        dispsocket_t *dispsocket = NULL;
        isc_result_t result;

        REQUIRE(VALID_DISPATCH(disp));
        REQUIRE(task != NULL);
        REQUIRE(dest != NULL);
        REQUIRE(resp != NULL && *resp == NULL);
        REQUIRE(idp != NULL);
        if ((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0)
                REQUIRE(sockmgr != NULL);

        LOCK(&disp->lock);

        if (disp->shutting_down == 1) {
                UNLOCK(&disp->lock);
                return (ISC_R_SHUTTINGDOWN);
        }

        if (disp->requests >= disp->maxrequests) {
                UNLOCK(&disp->lock);
                return (ISC_R_QUOTA);
        }

        if ((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0 &&
            disp->nsockets > DNS_DISPATCH_SOCKSQUOTA) {
                dispsocket_t *oldestsocket;
                dns_dispentry_t *oldestresp;
                dns_dispatchevent_t *rev;

                /*
                 * Kill oldest outstanding query if the number of sockets
                 * exceeds the quota to keep the room for new queries.
                 */
                oldestsocket = ISC_LIST_HEAD(disp->activesockets);
                oldestresp = oldestsocket->resp;
                if (oldestresp != NULL && !oldestresp->item_out) {
                        rev = allocate_devent(oldestresp->disp);
                        if (rev != NULL) {
                                rev->buffer.base = NULL;
                                rev->result = ISC_R_CANCELED;
                                rev->id = oldestresp->id;
                                ISC_EVENT_INIT(rev, sizeof(*rev), 0,
                                               NULL, DNS_EVENT_DISPATCH,
                                               oldestresp->action,
                                               oldestresp->arg, oldestresp,
                                               NULL, NULL);
                                oldestresp->item_out = ISC_TRUE;
                                isc_task_send(oldestresp->task,
                                              ISC_EVENT_PTR(&rev));
                                inc_stats(disp->mgr,
                                          dns_resstatscounter_dispabort);
                        }
                }

                /*
                 * Move this entry to the tail so that it won't (easily) be
                 * examined before actually being canceled.
                 */
                ISC_LIST_UNLINK(disp->activesockets, oldestsocket, link);
                ISC_LIST_APPEND(disp->activesockets, oldestsocket, link);
        }

        qid = DNS_QID(disp);

        if ((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0) {
                /*
                 * Get a separate UDP socket with a random port number.
                 */
                result = get_dispsocket(disp, dest, sockmgr, &dispsocket,
                                        &localport);
                if (result != ISC_R_SUCCESS) {
                        UNLOCK(&disp->lock);
                        inc_stats(disp->mgr, dns_resstatscounter_dispsockfail);
                        return (result);
                }
        } else {
                localport = disp->localport;
        }

        /*
         * Try somewhat hard to find an unique ID unless FIXEDID is set
         * in which case we use the id passed in via *idp.
         */
        LOCK(&qid->lock);
        if ((options & DNS_DISPATCHOPT_FIXEDID) != 0)
                id = *idp;
        else
                id = (dns_messageid_t)isc_rng_random(DISP_RNGCTX(disp));
        ok = ISC_FALSE;
        i = 0;
        do {
                bucket = dns_hash(qid, dest, id, localport);
                if (entry_search(qid, dest, id, localport, bucket) == NULL) {
                        ok = ISC_TRUE;
                        break;
                }
                if ((disp->attributes & DNS_DISPATCHATTR_FIXEDID) != 0)
                        break;
                id += qid->qid_increment;
                id &= 0x0000ffff;
        } while (i++ < 64);
        UNLOCK(&qid->lock);

        if (!ok) {
                UNLOCK(&disp->lock);
                return (ISC_R_NOMORE);
        }

        res = isc_mempool_get(disp->mgr->rpool);
        if (res == NULL) {
                if (dispsocket != NULL)
                        destroy_dispsocket(disp, &dispsocket);
                UNLOCK(&disp->lock);
                return (ISC_R_NOMEMORY);
        }

        disp->refcount++;
        disp->requests++;
        res->task = NULL;
        isc_task_attach(task, &res->task);
        res->disp = disp;
        res->id = id;
        res->port = localport;
        res->bucket = bucket;
        res->host = *dest;
        res->action = action;
        res->arg = arg;
        res->dispsocket = dispsocket;
        if (dispsocket != NULL)
                dispsocket->resp = res;
        res->item_out = ISC_FALSE;
        ISC_LIST_INIT(res->items);
        ISC_LINK_INIT(res, link);
        res->magic = RESPONSE_MAGIC;

        LOCK(&qid->lock);
        ISC_LIST_APPEND(qid->qid_table[bucket], res, link);
        UNLOCK(&qid->lock);

        inc_stats(disp->mgr, (qid == disp->mgr->qid) ?
                             dns_resstatscounter_disprequdp :
                             dns_resstatscounter_dispreqtcp);

        request_log(disp, res, LVL(90),
                    "attached to task %p", res->task);

        if (((disp->attributes & DNS_DISPATCHATTR_UDP) != 0) ||
            ((disp->attributes & DNS_DISPATCHATTR_CONNECTED) != 0)) {
                result = startrecv(disp, dispsocket);
                if (result != ISC_R_SUCCESS) {
                        LOCK(&qid->lock);
                        ISC_LIST_UNLINK(qid->qid_table[bucket], res, link);
                        UNLOCK(&qid->lock);

                        if (dispsocket != NULL)
                                destroy_dispsocket(disp, &dispsocket);

                        disp->refcount--;
                        disp->requests--;

                        dec_stats(disp->mgr, (qid == disp->mgr->qid) ?
                                             dns_resstatscounter_disprequdp :
                                             dns_resstatscounter_dispreqtcp);

                        UNLOCK(&disp->lock);
                        isc_task_detach(&res->task);
                        isc_mempool_put(disp->mgr->rpool, res);
                        return (result);
                }
        }

        if (dispsocket != NULL)
                ISC_LIST_APPEND(disp->activesockets, dispsocket, link);

        UNLOCK(&disp->lock);

        *idp = id;
        *resp = res;

        if ((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0)
                INSIST(res->dispsocket != NULL);

        return (ISC_R_SUCCESS);
}

isc_result_t
dns_dispatch_addresponse(dns_dispatch_t *disp, isc_sockaddr_t *dest,
                         isc_task_t *task, isc_taskaction_t action, void *arg,
                         dns_messageid_t *idp, dns_dispentry_t **resp)
{
        REQUIRE(VALID_DISPATCH(disp));
        REQUIRE((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) == 0);

        return (dns_dispatch_addresponse3(disp, 0, dest, task, action, arg,
                                          idp, resp, NULL));
}

void
dns_dispatch_starttcp(dns_dispatch_t *disp) {

        REQUIRE(VALID_DISPATCH(disp));

        dispatch_log(disp, LVL(90), "starttcp %p", disp->task[0]);

        LOCK(&disp->lock);
        if ((disp->attributes & DNS_DISPATCHATTR_CONNECTED) == 0) {
                disp->attributes |= DNS_DISPATCHATTR_CONNECTED;
                (void)startrecv(disp, NULL);
        }
        UNLOCK(&disp->lock);
}

void
dns_dispatch_removeresponse(dns_dispentry_t **resp,
                            dns_dispatchevent_t **sockevent)
{
        dns_dispatchmgr_t *mgr;
        dns_dispatch_t *disp;
        dns_dispentry_t *res;
        dispsocket_t *dispsock;
        dns_dispatchevent_t *ev;
        unsigned int bucket;
        isc_boolean_t killit;
        unsigned int n;
        isc_eventlist_t events;
        dns_qid_t *qid;

        REQUIRE(resp != NULL);
        REQUIRE(VALID_RESPONSE(*resp));

        res = *resp;
        *resp = NULL;

        disp = res->disp;
        REQUIRE(VALID_DISPATCH(disp));
        mgr = disp->mgr;
        REQUIRE(VALID_DISPATCHMGR(mgr));

        qid = DNS_QID(disp);

        if (sockevent != NULL) {
                REQUIRE(*sockevent != NULL);
                ev = *sockevent;
                *sockevent = NULL;
        } else {
                ev = NULL;
        }

        LOCK(&disp->lock);

        INSIST(disp->requests > 0);
        disp->requests--;
        dec_stats(disp->mgr, (qid == disp->mgr->qid) ?
                             dns_resstatscounter_disprequdp :
                             dns_resstatscounter_dispreqtcp);
        INSIST(disp->refcount > 0);
        disp->refcount--;
        if (disp->refcount == 0) {
                if (disp->recv_pending > 0)
                        isc_socket_cancel(disp->socket, disp->task[0],
                                          ISC_SOCKCANCEL_RECV);
                for (dispsock = ISC_LIST_HEAD(disp->activesockets);
                     dispsock != NULL;
                     dispsock = ISC_LIST_NEXT(dispsock, link)) {
                        isc_socket_cancel(dispsock->socket, dispsock->task,
                                          ISC_SOCKCANCEL_RECV);
                }
                disp->shutting_down = 1;
        }

        bucket = res->bucket;

        LOCK(&qid->lock);
        ISC_LIST_UNLINK(qid->qid_table[bucket], res, link);
        UNLOCK(&qid->lock);

        if (ev == NULL && res->item_out) {
                /*
                 * We've posted our event, but the caller hasn't gotten it
                 * yet.  Take it back.
                 */
                ISC_LIST_INIT(events);
                n = isc_task_unsend(res->task, res, DNS_EVENT_DISPATCH,
                                    NULL, &events);
                /*
                 * We had better have gotten it back.
                 */
                INSIST(n == 1);
                ev = (dns_dispatchevent_t *)ISC_LIST_HEAD(events);
        }

        if (ev != NULL) {
                REQUIRE(res->item_out == ISC_TRUE);
                res->item_out = ISC_FALSE;
                if (ev->buffer.base != NULL)
                        free_buffer(disp, ev->buffer.base, ev->buffer.length);
                free_devent(disp, ev);
        }

        request_log(disp, res, LVL(90), "detaching from task %p", res->task);
        isc_task_detach(&res->task);

        if (res->dispsocket != NULL) {
                isc_socket_cancel(res->dispsocket->socket,
                                  res->dispsocket->task, ISC_SOCKCANCEL_RECV);
                res->dispsocket->resp = NULL;
        }

        /*
         * Free any buffered requests as well
         */
        ev = ISC_LIST_HEAD(res->items);
        while (ev != NULL) {
                ISC_LIST_UNLINK(res->items, ev, ev_link);
                if (ev->buffer.base != NULL)
                        free_buffer(disp, ev->buffer.base, ev->buffer.length);
                free_devent(disp, ev);
                ev = ISC_LIST_HEAD(res->items);
        }
        res->magic = 0;
        isc_mempool_put(disp->mgr->rpool, res);
        if (disp->shutting_down == 1)
                do_cancel(disp);
        else
                (void)startrecv(disp, NULL);

        killit = destroy_disp_ok(disp);
        UNLOCK(&disp->lock);
        if (killit)
                isc_task_send(disp->task[0], &disp->ctlevent);
}

static void
do_cancel(dns_dispatch_t *disp) {
        dns_dispatchevent_t *ev;
        dns_dispentry_t *resp;
        dns_qid_t *qid;

        if (disp->shutdown_out == 1)
                return;

        qid = DNS_QID(disp);

        /*
         * Search for the first response handler without packets outstanding
         * unless a specific hander is given.
         */
        LOCK(&qid->lock);
        for (resp = linear_first(qid);
             resp != NULL && resp->item_out;
             /* Empty. */)
                resp = linear_next(qid, resp);

        /*
         * No one to send the cancel event to, so nothing to do.
         */
        if (resp == NULL)
                goto unlock;

        /*
         * Send the shutdown failsafe event to this resp.
         */
        ev = disp->failsafe_ev;
        ISC_EVENT_INIT(ev, sizeof(*ev), 0, NULL, DNS_EVENT_DISPATCH,
                       resp->action, resp->arg, resp, NULL, NULL);
        ev->result = disp->shutdown_why;
        ev->buffer.base = NULL;
        ev->buffer.length = 0;
        disp->shutdown_out = 1;
        request_log(disp, resp, LVL(10),
                    "cancel: failsafe event %p -> task %p",
                    ev, resp->task);
        resp->item_out = ISC_TRUE;
        isc_task_send(resp->task, ISC_EVENT_PTR(&ev));
 unlock:
        UNLOCK(&qid->lock);
}

isc_socket_t *
dns_dispatch_getsocket(dns_dispatch_t *disp) {
        REQUIRE(VALID_DISPATCH(disp));

        return (disp->socket);
}

isc_socket_t *
dns_dispatch_getentrysocket(dns_dispentry_t *resp) {
        REQUIRE(VALID_RESPONSE(resp));

        if (resp->dispsocket != NULL)
                return (resp->dispsocket->socket);
        else
                return (NULL);
}

isc_result_t
dns_dispatch_getlocaladdress(dns_dispatch_t *disp, isc_sockaddr_t *addrp) {

        REQUIRE(VALID_DISPATCH(disp));
        REQUIRE(addrp != NULL);

        if (disp->socktype == isc_sockettype_udp) {
                *addrp = disp->local;
                return (ISC_R_SUCCESS);
        }
        return (ISC_R_NOTIMPLEMENTED);
}

void
dns_dispatch_cancel(dns_dispatch_t *disp) {
        REQUIRE(VALID_DISPATCH(disp));

        LOCK(&disp->lock);

        if (disp->shutting_down == 1) {
                UNLOCK(&disp->lock);
                return;
        }

        disp->shutdown_why = ISC_R_CANCELED;
        disp->shutting_down = 1;
        do_cancel(disp);

        UNLOCK(&disp->lock);

        return;
}

unsigned int
dns_dispatch_getattributes(dns_dispatch_t *disp) {
        REQUIRE(VALID_DISPATCH(disp));

        /*
         * We don't bother locking disp here; it's the caller's responsibility
         * to use only non volatile flags.
         */
        return (disp->attributes);
}

void
dns_dispatch_changeattributes(dns_dispatch_t *disp,
                              unsigned int attributes, unsigned int mask)
{
        REQUIRE(VALID_DISPATCH(disp));
        /* Exclusive attribute can only be set on creation */
        REQUIRE((attributes & DNS_DISPATCHATTR_EXCLUSIVE) == 0);
        /* Also, a dispatch with randomport specified cannot start listening */
        REQUIRE((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) == 0 ||
                (attributes & DNS_DISPATCHATTR_NOLISTEN) == 0);

        /* XXXMLG
         * Should check for valid attributes here!
         */

        LOCK(&disp->lock);

        if ((mask & DNS_DISPATCHATTR_NOLISTEN) != 0) {
                if ((disp->attributes & DNS_DISPATCHATTR_NOLISTEN) != 0 &&
                    (attributes & DNS_DISPATCHATTR_NOLISTEN) == 0) {
                        disp->attributes &= ~DNS_DISPATCHATTR_NOLISTEN;
                        (void)startrecv(disp, NULL);
                } else if ((disp->attributes & DNS_DISPATCHATTR_NOLISTEN)
                           == 0 &&
                           (attributes & DNS_DISPATCHATTR_NOLISTEN) != 0) {
                        disp->attributes |= DNS_DISPATCHATTR_NOLISTEN;
                        if (disp->recv_pending != 0)
                                isc_socket_cancel(disp->socket, disp->task[0],
                                                  ISC_SOCKCANCEL_RECV);
                }
        }

        disp->attributes &= ~mask;
        disp->attributes |= (attributes & mask);
        UNLOCK(&disp->lock);
}

void
dns_dispatch_importrecv(dns_dispatch_t *disp, isc_event_t *event) {
        void *buf;
        isc_socketevent_t *sevent, *newsevent;

        REQUIRE(VALID_DISPATCH(disp));
        REQUIRE((disp->attributes & DNS_DISPATCHATTR_NOLISTEN) != 0);
        REQUIRE(event != NULL);

        sevent = (isc_socketevent_t *)event;

        INSIST(sevent->n <= disp->mgr->buffersize);
        newsevent = (isc_socketevent_t *)
                    isc_event_allocate(disp->mgr->mctx, NULL,
                                      DNS_EVENT_IMPORTRECVDONE, udp_shrecv,
                                      disp, sizeof(isc_socketevent_t));
        if (newsevent == NULL)
                return;

        buf = allocate_udp_buffer(disp);
        if (buf == NULL) {
                isc_event_free(ISC_EVENT_PTR(&newsevent));
                return;
        }
        memmove(buf, sevent->region.base, sevent->n);
        newsevent->region.base = buf;
        newsevent->region.length = disp->mgr->buffersize;
        newsevent->n = sevent->n;
        newsevent->result = sevent->result;
        newsevent->address = sevent->address;
        newsevent->timestamp = sevent->timestamp;
        newsevent->pktinfo = sevent->pktinfo;
        newsevent->attributes = sevent->attributes;

        isc_task_send(disp->task[0], ISC_EVENT_PTR(&newsevent));
}

dns_dispatch_t *
dns_dispatchset_get(dns_dispatchset_t *dset) {
        dns_dispatch_t *disp;

        /* check that dispatch set is configured */
        if (dset == NULL || dset->ndisp == 0)
                return (NULL);

        LOCK(&dset->lock);
        disp = dset->dispatches[dset->cur];
        dset->cur++;
        if (dset->cur == dset->ndisp)
                dset->cur = 0;
        UNLOCK(&dset->lock);

        return (disp);
}

isc_result_t
dns_dispatchset_create(isc_mem_t *mctx, isc_socketmgr_t *sockmgr,
                       isc_taskmgr_t *taskmgr, dns_dispatch_t *source,
                       dns_dispatchset_t **dsetp, int n)
{
        isc_result_t result;
        dns_dispatchset_t *dset;
        dns_dispatchmgr_t *mgr;
        int i, j;

        REQUIRE(VALID_DISPATCH(source));
        REQUIRE((source->attributes & DNS_DISPATCHATTR_UDP) != 0);
        REQUIRE(dsetp != NULL && *dsetp == NULL);

        mgr = source->mgr;

        dset = isc_mem_get(mctx, sizeof(dns_dispatchset_t));
        if (dset == NULL)
                return (ISC_R_NOMEMORY);
        memset(dset, 0, sizeof(*dset));

        result = isc_mutex_init(&dset->lock);
        if (result != ISC_R_SUCCESS)
                goto fail_alloc;

        dset->dispatches = isc_mem_get(mctx, sizeof(dns_dispatch_t *) * n);
        if (dset->dispatches == NULL) {
                result = ISC_R_NOMEMORY;
                goto fail_lock;
        }

        isc_mem_attach(mctx, &dset->mctx);
        dset->ndisp = n;
        dset->cur = 0;

        dset->dispatches[0] = NULL;
        dns_dispatch_attach(source, &dset->dispatches[0]);

        LOCK(&mgr->lock);
        for (i = 1; i < n; i++) {
                dset->dispatches[i] = NULL;
                result = dispatch_createudp(mgr, sockmgr, taskmgr,
                                            &source->local,
                                            source->maxrequests,
                                            source->attributes,
                                            &dset->dispatches[i],
                                            source->socket);
                if (result != ISC_R_SUCCESS)
                        goto fail;
        }

        UNLOCK(&mgr->lock);
        *dsetp = dset;

        return (ISC_R_SUCCESS);

 fail:
        UNLOCK(&mgr->lock);

        for (j = 0; j < i; j++)
                dns_dispatch_detach(&(dset->dispatches[j]));
        isc_mem_put(mctx, dset->dispatches, sizeof(dns_dispatch_t *) * n);
        if (dset->mctx == mctx)
                isc_mem_detach(&dset->mctx);

 fail_lock:
        DESTROYLOCK(&dset->lock);

 fail_alloc:
        isc_mem_put(mctx, dset, sizeof(dns_dispatchset_t));
        return (result);
}

void
dns_dispatchset_cancelall(dns_dispatchset_t *dset, isc_task_t *task) {
        int i;

        REQUIRE(dset != NULL);

        for (i = 0; i < dset->ndisp; i++) {
                isc_socket_t *sock;
                sock = dns_dispatch_getsocket(dset->dispatches[i]);
                isc_socket_cancel(sock, task, ISC_SOCKCANCEL_ALL);
        }
}

void
dns_dispatchset_destroy(dns_dispatchset_t **dsetp) {
        dns_dispatchset_t *dset;
        int i;

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

        dset = *dsetp;
        for (i = 0; i < dset->ndisp; i++)
                dns_dispatch_detach(&(dset->dispatches[i]));
        isc_mem_put(dset->mctx, dset->dispatches,
                    sizeof(dns_dispatch_t *) * dset->ndisp);
        DESTROYLOCK(&dset->lock);
        isc_mem_putanddetach(&dset->mctx, dset, sizeof(dns_dispatchset_t));

        *dsetp = NULL;
}

void
dns_dispatch_setdscp(dns_dispatch_t *disp, isc_dscp_t dscp) {
        REQUIRE(VALID_DISPATCH(disp));
        disp->dscp = dscp;
}

isc_dscp_t
dns_dispatch_getdscp(dns_dispatch_t *disp) {
        REQUIRE(VALID_DISPATCH(disp));
        return (disp->dscp);
}

#if 0
void
dns_dispatchmgr_dump(dns_dispatchmgr_t *mgr) {
        dns_dispatch_t *disp;
        char foo[1024];

        disp = ISC_LIST_HEAD(mgr->list);
        while (disp != NULL) {
                isc_sockaddr_format(&disp->local, foo, sizeof(foo));
                printf("\tdispatch %p, addr %s\n", disp, foo);
                disp = ISC_LIST_NEXT(disp, link);
        }
}
#endif

---