lib/dns/db.c

	db.c revision dafcb997e390efa4423883dafd100c975c4095d6
/*
 * Copyright (C) 2004  Internet Systems Consortium, Inc. ("ISC")
 * Copyright (C) 1999-2001, 2003  Internet Software Consortium.
 *
 * Permission to use, copy, modify, and 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.
 */

/* $Id: db.c,v 1.74 2004/03/05 05:09:18 marka Exp $ */

/***
 *** Imports
 ***/

#include <config.h>

#include <isc/buffer.h>
#include <isc/mem.h>
#include <isc/once.h>
#include <isc/rwlock.h>
#include <isc/string.h>
#include <isc/util.h>

#include <dns/callbacks.h>
#include <dns/db.h>
#include <dns/log.h>
#include <dns/master.h>
#include <dns/rdata.h>
#include <dns/rdataset.h>
#include <dns/result.h>

/***
 *** Private Types
 ***/

struct dns_dbimplementation {
    const char *                name;
    dns_dbcreatefunc_t          create;
    isc_mem_t *             mctx;
    void *                  driverarg;
    ISC_LINK(dns_dbimplementation_t)    link;
};

/***
 *** Supported DB Implementations Registry
 ***/

/*
 * Built in database implementations are registered here.
 */

#include "rbtdb.h"
#include "rbtdb64.h"

static ISC_LIST(dns_dbimplementation_t) implementations;
static isc_rwlock_t implock;
static isc_once_t once = ISC_ONCE_INIT;

static dns_dbimplementation_t rbtimp;
static dns_dbimplementation_t rbt64imp;

static void
initialize(void) {
    RUNTIME_CHECK(isc_rwlock_init(&implock, 0, 0) == ISC_R_SUCCESS);

    rbtimp.name = "rbt";
    rbtimp.create = dns_rbtdb_create;
    rbtimp.mctx = NULL;
    rbtimp.driverarg = NULL;
    ISC_LINK_INIT(&rbtimp, link);

    rbt64imp.name = "rbt64";
    rbt64imp.create = dns_rbtdb64_create;
    rbt64imp.mctx = NULL;
    rbt64imp.driverarg = NULL;
    ISC_LINK_INIT(&rbt64imp, link);

    ISC_LIST_INIT(implementations);
    ISC_LIST_APPEND(implementations, &rbtimp, link);
    ISC_LIST_APPEND(implementations, &rbt64imp, link);
}

static inline dns_dbimplementation_t *
impfind(const char *name) {
    dns_dbimplementation_t *imp;

    for (imp = ISC_LIST_HEAD(implementations);
         imp != NULL;
         imp = ISC_LIST_NEXT(imp, link))
        if (strcasecmp(name, imp->name) == 0)
            return (imp);
    return (NULL);
}


/***
 *** Basic DB Methods
 ***/

isc_result_t
dns_db_create(isc_mem_t *mctx, const char *db_type, dns_name_t *origin,
          dns_dbtype_t type, dns_rdataclass_t rdclass,
          unsigned int argc, char *argv[], dns_db_t **dbp)
{
    dns_dbimplementation_t *impinfo;

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

    /*
     * Create a new database using implementation 'db_type'.
     */

    REQUIRE(dbp != NULL && *dbp == NULL);
    REQUIRE(dns_name_isabsolute(origin));

    RWLOCK(&implock, isc_rwlocktype_read);
    impinfo = impfind(db_type);
    if (impinfo != NULL) {
        isc_result_t result;
        result = ((impinfo->create)(mctx, origin, type,
                        rdclass, argc, argv,
                        impinfo->driverarg, dbp));
        RWUNLOCK(&implock, isc_rwlocktype_read);
        return (result);
    }

    RWUNLOCK(&implock, isc_rwlocktype_read);

    isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE,
              DNS_LOGMODULE_DB, ISC_LOG_ERROR,
              "unsupported database type '%s'", db_type);

    return (ISC_R_NOTFOUND);
}

void
dns_db_attach(dns_db_t *source, dns_db_t **targetp) {

    /*
     * Attach *targetp to source.
     */

    REQUIRE(DNS_DB_VALID(source));
    REQUIRE(targetp != NULL && *targetp == NULL);

    (source->methods->attach)(source, targetp);

    ENSURE(*targetp == source);
}

void
dns_db_detach(dns_db_t **dbp) {

    /*
     * Detach *dbp from its database.
     */

    REQUIRE(dbp != NULL);
    REQUIRE(DNS_DB_VALID(*dbp));

    ((*dbp)->methods->detach)(dbp);

    ENSURE(*dbp == NULL);
}

isc_result_t
dns_db_ondestroy(dns_db_t *db, isc_task_t *task, isc_event_t **eventp)
{
    REQUIRE(DNS_DB_VALID(db));

    return (isc_ondestroy_register(&db->ondest, task, eventp));
}


isc_boolean_t
dns_db_iscache(dns_db_t *db) {

    /*
     * Does 'db' have cache semantics?
     */

    REQUIRE(DNS_DB_VALID(db));

    if ((db->attributes & DNS_DBATTR_CACHE) != 0)
        return (ISC_TRUE);

    return (ISC_FALSE);
}

isc_boolean_t
dns_db_iszone(dns_db_t *db) {

    /*
     * Does 'db' have zone semantics?
     */

    REQUIRE(DNS_DB_VALID(db));

    if ((db->attributes & (DNS_DBATTR_CACHE|DNS_DBATTR_STUB)) == 0)
        return (ISC_TRUE);

    return (ISC_FALSE);
}

isc_boolean_t
dns_db_isstub(dns_db_t *db) {

    /*
     * Does 'db' have stub semantics?
     */

    REQUIRE(DNS_DB_VALID(db));

    if ((db->attributes & DNS_DBATTR_STUB) != 0)
        return (ISC_TRUE);

    return (ISC_FALSE);
}

isc_boolean_t
dns_db_issecure(dns_db_t *db) {

    /*
     * Is 'db' secure?
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE((db->attributes & DNS_DBATTR_CACHE) == 0);

    return ((db->methods->issecure)(db));
}

isc_boolean_t
dns_db_ispersistent(dns_db_t *db) {

    /*
     * Is 'db' persistent?
     */

    REQUIRE(DNS_DB_VALID(db));

    return ((db->methods->ispersistent)(db));
}

dns_name_t *
dns_db_origin(dns_db_t *db) {
    /*
     * The origin of the database.
     */

    REQUIRE(DNS_DB_VALID(db));

    return (&db->origin);
}

dns_rdataclass_t
dns_db_class(dns_db_t *db) {
    /*
     * The class of the database.
     */

    REQUIRE(DNS_DB_VALID(db));

    return (db->rdclass);
}

isc_result_t
dns_db_beginload(dns_db_t *db, dns_addrdatasetfunc_t *addp,
         dns_dbload_t **dbloadp) {
    /*
     * Begin loading 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(addp != NULL && *addp == NULL);
    REQUIRE(dbloadp != NULL && *dbloadp == NULL);

    return ((db->methods->beginload)(db, addp, dbloadp));
}

isc_result_t
dns_db_endload(dns_db_t *db, dns_dbload_t **dbloadp) {
    /*
     * Finish loading 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(dbloadp != NULL && *dbloadp != NULL);

    return ((db->methods->endload)(db, dbloadp));
}

isc_result_t
dns_db_load(dns_db_t *db, const char *filename) {
    isc_result_t result, eresult;
    dns_rdatacallbacks_t callbacks;
    unsigned int options = 0;

    /*
     * Load master file 'filename' into 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));

    if ((db->attributes & DNS_DBATTR_CACHE) != 0)
        options |= DNS_MASTER_AGETTL;

    dns_rdatacallbacks_init(&callbacks);

    result = dns_db_beginload(db, &callbacks.add, &callbacks.add_private);
    if (result != ISC_R_SUCCESS)
        return (result);
    result = dns_master_loadfile(filename, &db->origin, &db->origin,
                     db->rdclass, options,
                     &callbacks, db->mctx);
    eresult = dns_db_endload(db, &callbacks.add_private);
    /*
     * We always call dns_db_endload(), but we only want to return its
     * result if dns_master_loadfile() succeeded.  If dns_master_loadfile()
     * failed, we want to return the result code it gave us.
     */
    if (eresult != ISC_R_SUCCESS &&
        (result == ISC_R_SUCCESS || result == DNS_R_SEENINCLUDE))
        result = eresult;

    return (result);
}

isc_result_t
dns_db_dump(dns_db_t *db, dns_dbversion_t *version, const char *filename) {
    /*
     * Dump 'db' into master file 'filename'.
     */

    REQUIRE(DNS_DB_VALID(db));

    return ((db->methods->dump)(db, version, filename));
}

/***
 *** Version Methods
 ***/

void
dns_db_currentversion(dns_db_t *db, dns_dbversion_t **versionp) {

    /*
     * Open the current version for reading.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE((db->attributes & DNS_DBATTR_CACHE) == 0);
    REQUIRE(versionp != NULL && *versionp == NULL);

    (db->methods->currentversion)(db, versionp);
}

isc_result_t
dns_db_newversion(dns_db_t *db, dns_dbversion_t **versionp) {

    /*
     * Open a new version for reading and writing.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE((db->attributes & DNS_DBATTR_CACHE) == 0);
    REQUIRE(versionp != NULL && *versionp == NULL);

    return ((db->methods->newversion)(db, versionp));
}

void
dns_db_attachversion(dns_db_t *db, dns_dbversion_t *source,
             dns_dbversion_t **targetp)
{
    /*
     * Attach '*targetp' to 'source'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE((db->attributes & DNS_DBATTR_CACHE) == 0);
    REQUIRE(source != NULL);
    REQUIRE(targetp != NULL && *targetp == NULL);

    (db->methods->attachversion)(db, source, targetp);

    ENSURE(*targetp != NULL);
}

void
dns_db_closeversion(dns_db_t *db, dns_dbversion_t **versionp,
            isc_boolean_t commit)
{

    /*
     * Close version '*versionp'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE((db->attributes & DNS_DBATTR_CACHE) == 0);
    REQUIRE(versionp != NULL && *versionp != NULL);

    (db->methods->closeversion)(db, versionp, commit);

    ENSURE(*versionp == NULL);
}

/***
 *** Node Methods
 ***/

isc_result_t
dns_db_findnode(dns_db_t *db, dns_name_t *name,
        isc_boolean_t create, dns_dbnode_t **nodep)
{

    /*
     * Find the node with name 'name'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(nodep != NULL && *nodep == NULL);

    return ((db->methods->findnode)(db, name, create, nodep));
}

isc_result_t
dns_db_find(dns_db_t *db, dns_name_t *name, dns_dbversion_t *version,
        dns_rdatatype_t type, unsigned int options, isc_stdtime_t now,
        dns_dbnode_t **nodep, dns_name_t *foundname,
        dns_rdataset_t *rdataset, dns_rdataset_t *sigrdataset)
{

    /*
     * Find the best match for 'name' and 'type' in version 'version'
     * of 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(type != dns_rdatatype_rrsig);
    REQUIRE(nodep == NULL || (nodep != NULL && *nodep == NULL));
    REQUIRE(dns_name_hasbuffer(foundname));
    REQUIRE(rdataset == NULL ||
        (DNS_RDATASET_VALID(rdataset) &&
         ! dns_rdataset_isassociated(rdataset)));
    REQUIRE(sigrdataset == NULL ||
        (DNS_RDATASET_VALID(sigrdataset) &&
         ! dns_rdataset_isassociated(sigrdataset)));

    return ((db->methods->find)(db, name, version, type, options, now,
                    nodep, foundname, rdataset, sigrdataset));
}

isc_result_t
dns_db_findzonecut(dns_db_t *db, dns_name_t *name,
           unsigned int options, isc_stdtime_t now,
           dns_dbnode_t **nodep, dns_name_t *foundname,
           dns_rdataset_t *rdataset, dns_rdataset_t *sigrdataset)
{
    /*
     * Find the deepest known zonecut which encloses 'name' in 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE((db->attributes & DNS_DBATTR_CACHE) != 0);
    REQUIRE(nodep == NULL || (nodep != NULL && *nodep == NULL));
    REQUIRE(dns_name_hasbuffer(foundname));
    REQUIRE(sigrdataset == NULL ||
        (DNS_RDATASET_VALID(sigrdataset) &&
         ! dns_rdataset_isassociated(sigrdataset)));

    return ((db->methods->findzonecut)(db, name, options, now, nodep,
                       foundname, rdataset, sigrdataset));
}

void
dns_db_attachnode(dns_db_t *db, dns_dbnode_t *source, dns_dbnode_t **targetp) {

    /*
     * Attach *targetp to source.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(source != NULL);
    REQUIRE(targetp != NULL && *targetp == NULL);

    (db->methods->attachnode)(db, source, targetp);
}

void
dns_db_detachnode(dns_db_t *db, dns_dbnode_t **nodep) {

    /*
     * Detach *nodep from its node.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(nodep != NULL && *nodep != NULL);

    (db->methods->detachnode)(db, nodep);

    ENSURE(*nodep == NULL);
}

isc_result_t
dns_db_expirenode(dns_db_t *db, dns_dbnode_t *node, isc_stdtime_t now) {

    /*
     * Mark as stale all records at 'node' which expire at or before 'now'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE((db->attributes & DNS_DBATTR_CACHE) != 0);
    REQUIRE(node != NULL);

    return ((db->methods->expirenode)(db, node, now));
}

void
dns_db_printnode(dns_db_t *db, dns_dbnode_t *node, FILE *out) {
    /*
     * Print a textual representation of the contents of the node to
     * 'out'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(node != NULL);

    (db->methods->printnode)(db, node, out);
}

/***
 *** DB Iterator Creation
 ***/

isc_result_t
dns_db_createiterator(dns_db_t *db, isc_boolean_t relative_names,
              dns_dbiterator_t **iteratorp)
{
    /*
     * Create an iterator for version 'version' of 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(iteratorp != NULL && *iteratorp == NULL);

    return (db->methods->createiterator(db, relative_names, iteratorp));
}

/***
 *** Rdataset Methods
 ***/

isc_result_t
dns_db_findrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
            dns_rdatatype_t type, dns_rdatatype_t covers,
            isc_stdtime_t now, dns_rdataset_t *rdataset,
            dns_rdataset_t *sigrdataset)
{
    /*
     * Search for an rdataset of type 'type' at 'node' that are in version
     * 'version' of 'db'.  If found, make 'rdataset' refer to it.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(node != NULL);
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(! dns_rdataset_isassociated(rdataset));
    REQUIRE(covers == 0 || type == dns_rdatatype_rrsig);
    REQUIRE(type != dns_rdatatype_any);
    REQUIRE(sigrdataset == NULL ||
        (DNS_RDATASET_VALID(sigrdataset) &&
         ! dns_rdataset_isassociated(sigrdataset)));

    return ((db->methods->findrdataset)(db, node, version, type, covers,
                        now, rdataset, sigrdataset));
}

isc_result_t
dns_db_allrdatasets(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
            isc_stdtime_t now, dns_rdatasetiter_t **iteratorp)
{
    /*
     * Make '*iteratorp' an rdataset iteratator for all rdatasets at
     * 'node' in version 'version' of 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(iteratorp != NULL && *iteratorp == NULL);

    return ((db->methods->allrdatasets)(db, node, version, now,
                        iteratorp));
}

isc_result_t
dns_db_addrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
           isc_stdtime_t now, dns_rdataset_t *rdataset,
           unsigned int options, dns_rdataset_t *addedrdataset)
{
    /*
     * Add 'rdataset' to 'node' in version 'version' of 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(node != NULL);
    REQUIRE(((db->attributes & DNS_DBATTR_CACHE) == 0 && version != NULL)||
        ((db->attributes & DNS_DBATTR_CACHE) != 0 &&
         version == NULL && (options & DNS_DBADD_MERGE) == 0));
    REQUIRE((options & DNS_DBADD_EXACT) == 0 ||
        (options & DNS_DBADD_MERGE) != 0);
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(dns_rdataset_isassociated(rdataset));
    REQUIRE(rdataset->rdclass == db->rdclass);
    REQUIRE(addedrdataset == NULL ||
        (DNS_RDATASET_VALID(addedrdataset) &&
         ! dns_rdataset_isassociated(addedrdataset)));

    return ((db->methods->addrdataset)(db, node, version, now, rdataset,
                       options, addedrdataset));
}

isc_result_t
dns_db_subtractrdataset(dns_db_t *db, dns_dbnode_t *node,
            dns_dbversion_t *version, dns_rdataset_t *rdataset,
            unsigned int options, dns_rdataset_t *newrdataset)
{
    /*
     * Remove any rdata in 'rdataset' from 'node' in version 'version' of
     * 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(node != NULL);
    REQUIRE((db->attributes & DNS_DBATTR_CACHE) == 0 && version != NULL);
    REQUIRE(DNS_RDATASET_VALID(rdataset));
    REQUIRE(dns_rdataset_isassociated(rdataset));
    REQUIRE(rdataset->rdclass == db->rdclass);
    REQUIRE(newrdataset == NULL ||
        (DNS_RDATASET_VALID(newrdataset) &&
         ! dns_rdataset_isassociated(newrdataset)));

    return ((db->methods->subtractrdataset)(db, node, version, rdataset,
                        options, newrdataset));
}

isc_result_t
dns_db_deleterdataset(dns_db_t *db, dns_dbnode_t *node,
              dns_dbversion_t *version, dns_rdatatype_t type,
              dns_rdatatype_t covers)
{
    /*
     * Make it so that no rdataset of type 'type' exists at 'node' in
     * version version 'version' of 'db'.
     */

    REQUIRE(DNS_DB_VALID(db));
    REQUIRE(node != NULL);
    REQUIRE(((db->attributes & DNS_DBATTR_CACHE) == 0 && version != NULL)||
        ((db->attributes & DNS_DBATTR_CACHE) != 0 && version == NULL));

    return ((db->methods->deleterdataset)(db, node, version,
                          type, covers));
}

void
dns_db_overmem(dns_db_t *db, isc_boolean_t overmem) {

    REQUIRE(DNS_DB_VALID(db));

    (db->methods->overmem)(db, overmem);
}

isc_result_t
dns_db_getsoaserial(dns_db_t *db, dns_dbversion_t *ver, isc_uint32_t *serialp)
{
    isc_result_t result;
    dns_dbnode_t *node = NULL;
    dns_rdataset_t rdataset;
    dns_rdata_t rdata = DNS_RDATA_INIT;
    isc_buffer_t buffer;

    REQUIRE(dns_db_iszone(db) || dns_db_isstub(db));

    result = dns_db_findnode(db, dns_db_origin(db), ISC_FALSE, &node);
    if (result != ISC_R_SUCCESS)
        return (result);

    dns_rdataset_init(&rdataset);
    result = dns_db_findrdataset(db, node, ver, dns_rdatatype_soa, 0,
                     (isc_stdtime_t)0, &rdataset, NULL);
    if (result != ISC_R_SUCCESS)
        goto freenode;

    result = dns_rdataset_first(&rdataset);
    if (result != ISC_R_SUCCESS)
        goto freerdataset;
    dns_rdataset_current(&rdataset, &rdata);
    result = dns_rdataset_next(&rdataset);
    INSIST(result == ISC_R_NOMORE);

    INSIST(rdata.length > 20);
    isc_buffer_init(&buffer, rdata.data, rdata.length);
    isc_buffer_add(&buffer, rdata.length);
    isc_buffer_forward(&buffer, rdata.length - 20);
    *serialp = isc_buffer_getuint32(&buffer);

    result = ISC_R_SUCCESS;

 freerdataset:
    dns_rdataset_disassociate(&rdataset);

 freenode:
    dns_db_detachnode(db, &node);
    return (result);
}

unsigned int
dns_db_nodecount(dns_db_t *db) {
    REQUIRE(DNS_DB_VALID(db));

    return ((db->methods->nodecount)(db));
}

void
dns_db_settask(dns_db_t *db, isc_task_t *task) {
    REQUIRE(DNS_DB_VALID(db));

    (db->methods->settask)(db, task);
}

isc_result_t
dns_db_register(const char *name, dns_dbcreatefunc_t create, void *driverarg,
        isc_mem_t *mctx, dns_dbimplementation_t **dbimp)
{
    dns_dbimplementation_t *imp;

    REQUIRE(name != NULL);
    REQUIRE(dbimp != NULL && *dbimp == NULL);

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

    RWLOCK(&implock, isc_rwlocktype_write);
    imp = impfind(name);
    if (imp != NULL) {
        RWUNLOCK(&implock, isc_rwlocktype_write);
        return (ISC_R_EXISTS);
    }

    imp = isc_mem_get(mctx, sizeof(dns_dbimplementation_t));
    if (imp == NULL) {
        RWUNLOCK(&implock, isc_rwlocktype_write);
        return (ISC_R_NOMEMORY);
    }
    imp->name = name;
    imp->create = create;
    imp->mctx = NULL;
    imp->driverarg = driverarg;
    isc_mem_attach(mctx, &imp->mctx);
    ISC_LINK_INIT(imp, link);
    ISC_LIST_APPEND(implementations, imp, link);
    RWUNLOCK(&implock, isc_rwlocktype_write);

    *dbimp = imp;

    return (ISC_R_SUCCESS);
}

void
dns_db_unregister(dns_dbimplementation_t **dbimp) {
    dns_dbimplementation_t *imp;
    isc_mem_t *mctx;

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

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

    imp = *dbimp;
    RWLOCK(&implock, isc_rwlocktype_write);
    ISC_LIST_UNLINK(implementations, imp, link);
    mctx = imp->mctx;
    isc_mem_put(mctx, imp, sizeof(dns_dbimplementation_t));
    isc_mem_detach(&mctx);
    RWUNLOCK(&implock, isc_rwlocktype_write);
}