dyndb/driver/db.c

/*
 * Database API implementation. The interface is defined in lib/dns/db.h.
 *
 * dns_db_*() calls on database instances backed by this driver use
 * struct sampledb_methods to find appropriate function implementation.
 *
 * This example re-uses RBT DB implementation from original BIND and blindly
 * proxies most of dns_db_*() calls to this underlying RBT DB.
 * See struct sampledb below.
 *
 * Copyright (C) 2009-2015  Red Hat ; see COPYRIGHT for license
 */
#include <config.h>

#include <isc/string.h>
#include <isc/util.h>

#include <dns/db.h>
#include <dns/diff.h>
#include <dns/enumclass.h>
#include <dns/rbt.h>
#include <dns/rdatalist.h>
#include <dns/rdatastruct.h>
#include <dns/soa.h>
#include <dns/types.h>

#include "db.h"
#include "instance.h"
#include "syncptr.h"
#include "util.h"

#define SAMPLEDB_MAGIC          ISC_MAGIC('S', 'M', 'D', 'B')
#define VALID_SAMPLEDB(sampledb) \
    ((sampledb) != NULL && (sampledb)->common.impmagic == SAMPLEDB_MAGIC)

struct sampledb {
    dns_db_t            common;
    isc_refcount_t          refs;
    sample_instance_t       *inst;

    /*
     * Internal RBT database implementation provided by BIND.
     * Most dns_db_* calls (find(), createiterator(), etc.)
     * are blindly forwarded to this RBT DB.
     */
    dns_db_t            *rbtdb;
};

typedef struct sampledb sampledb_t;

/*
 * Get full DNS name from the node.
 *
 * @warning
 * The code silently expects that "node" came from RBTDB and thus
 * assumption dns_dbnode_t (from RBTDB) == dns_rbtnode_t is correct.
 *
 * This should work as long as we use only RBTDB and nothing else.
 */
static isc_result_t
sample_name_fromnode(dns_dbnode_t *node, dns_name_t *name) {
    dns_rbtnode_t *rbtnode = (dns_rbtnode_t *) node;
    return (dns_rbt_fullnamefromnode(rbtnode, name));
}

static void
attach(dns_db_t *source, dns_db_t **targetp) {
    sampledb_t *sampledb = (sampledb_t *)source;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    isc_refcount_increment(&sampledb->refs, NULL);
    *targetp = source;
}

static void
free_sampledb(sampledb_t *sampledb) {
    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_detach(&sampledb->rbtdb);
    dns_name_free(&sampledb->common.origin, sampledb->common.mctx);
    isc_mem_putanddetach(&sampledb->common.mctx, sampledb, sizeof(*sampledb));
}

static void
detach(dns_db_t **dbp) {
    sampledb_t *sampledb = (sampledb_t *)(*dbp);
    unsigned int refs;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    isc_refcount_decrement(&sampledb->refs, &refs);
    if (refs == 0)
        free_sampledb(sampledb);
    *dbp = NULL;
}

/*
 * This method should never be called, because DB is "persistent".
 * See ispersistent() function. It means that database do not need to be
 * loaded in the usual sense.
 */
static isc_result_t
beginload(dns_db_t *db, dns_rdatacallbacks_t *callbacks) {
    UNUSED(db);
    UNUSED(callbacks);

    fatal_error("current implementation should never call beginload()");

    /* Not reached */
    return (ISC_R_SUCCESS);
}

/*
 * This method should never be called, because DB is "persistent".
 * See ispersistent() function. It means that database do not need to be
 * loaded in the usual sense.
 */
static isc_result_t
endload(dns_db_t *db, dns_rdatacallbacks_t *callbacks) {
    UNUSED(db);
    UNUSED(callbacks);

    fatal_error("current implementation should never call endload()");

    /* Not reached */
    return (ISC_R_SUCCESS);
}

static isc_result_t
serialize(dns_db_t *db, dns_dbversion_t *version, FILE *file) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_serialize(sampledb->rbtdb, version, file));
}

static isc_result_t
dump(dns_db_t *db, dns_dbversion_t *version, const char *filename,
     dns_masterformat_t masterformat)
{

    UNUSED(db);
    UNUSED(version);
    UNUSED(filename);
    UNUSED(masterformat);

    fatal_error("current implementation should never call dump()");

    /* Not reached */
    return (ISC_R_SUCCESS);
}

static void
currentversion(dns_db_t *db, dns_dbversion_t **versionp) {
    sampledb_t *sampledb = (sampledb_t *)db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_currentversion(sampledb->rbtdb, versionp);
}

static isc_result_t
newversion(dns_db_t *db, dns_dbversion_t **versionp) {
    sampledb_t *sampledb = (sampledb_t *)db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_newversion(sampledb->rbtdb, versionp));
}

static void
attachversion(dns_db_t *db, dns_dbversion_t *source,
          dns_dbversion_t **targetp)
{
    sampledb_t *sampledb = (sampledb_t *)db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_attachversion(sampledb->rbtdb, source, targetp);
}

static void
closeversion(dns_db_t *db, dns_dbversion_t **versionp, isc_boolean_t commit) {
    sampledb_t *sampledb = (sampledb_t *)db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_closeversion(sampledb->rbtdb, versionp, commit);
}

static isc_result_t
findnode(dns_db_t *db, dns_name_t *name, isc_boolean_t create,
     dns_dbnode_t **nodep)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_findnode(sampledb->rbtdb, name, create, nodep));
}

static isc_result_t
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)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_find(sampledb->rbtdb, name, version, type,
                options, now, nodep, foundname,
                rdataset, sigrdataset));
}

static isc_result_t
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)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_findzonecut(sampledb->rbtdb, name, options,
                   now, nodep, foundname, rdataset,
                   sigrdataset));
}

static void
attachnode(dns_db_t *db, dns_dbnode_t *source, dns_dbnode_t **targetp) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_attachnode(sampledb->rbtdb, source, targetp);

}

static void
detachnode(dns_db_t *db, dns_dbnode_t **targetp) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_detachnode(sampledb->rbtdb, targetp);
}

static isc_result_t
expirenode(dns_db_t *db, dns_dbnode_t *node, isc_stdtime_t now) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_expirenode(sampledb->rbtdb, node, now));
}

static void
printnode(dns_db_t *db, dns_dbnode_t *node, FILE *out) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_printnode(sampledb->rbtdb, node, out);
}

static isc_result_t
createiterator(dns_db_t *db, unsigned int options,
           dns_dbiterator_t **iteratorp)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_createiterator(sampledb->rbtdb, options, iteratorp));
}

static isc_result_t
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)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_findrdataset(sampledb->rbtdb, node, version, type,
                    covers, now, rdataset, sigrdataset));
}

static isc_result_t
allrdatasets(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
         isc_stdtime_t now, dns_rdatasetiter_t **iteratorp)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_allrdatasets(sampledb->rbtdb, node, version,
                    now, iteratorp));
}

static isc_result_t
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)
{
    sampledb_t *sampledb = (sampledb_t *) db;
    isc_result_t result;
    dns_fixedname_t name;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_fixedname_init(&name);
    CHECK(dns_db_addrdataset(sampledb->rbtdb, node, version, now,
                 rdataset, options, addedrdataset));
    if (rdataset->type == dns_rdatatype_a ||
        rdataset->type == dns_rdatatype_aaaa) {
        CHECK(sample_name_fromnode(node, dns_fixedname_name(&name)));
        CHECK(syncptrs(sampledb->inst, dns_fixedname_name(&name),
                   rdataset, DNS_DIFFOP_ADD));
    }

cleanup:
    return (result);
}

static isc_result_t
subtractrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
         dns_rdataset_t *rdataset, unsigned int options,
         dns_rdataset_t *newrdataset)
{
    sampledb_t *sampledb = (sampledb_t *) db;
    isc_result_t result;
    dns_fixedname_t name;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_fixedname_init(&name);
    result = dns_db_subtractrdataset(sampledb->rbtdb, node, version,
                     rdataset, options, newrdataset);
    if (result != ISC_R_SUCCESS && result != DNS_R_NXRRSET)
        goto cleanup;

    if (rdataset->type == dns_rdatatype_a ||
        rdataset->type == dns_rdatatype_aaaa) {
        CHECK(sample_name_fromnode(node, dns_fixedname_name(&name)));
        CHECK(syncptrs(sampledb->inst, dns_fixedname_name(&name),
                   rdataset, DNS_DIFFOP_DEL));
    }

cleanup:
    return (result);
}

/*
 * deleterdataset() function is not used during DNS update processing so syncptr
 * implementation is left as an exercise to the reader.
 */
static isc_result_t
deleterdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
           dns_rdatatype_t type, dns_rdatatype_t covers)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_deleterdataset(sampledb->rbtdb, node, version,
                      type, covers));
}

static isc_boolean_t
issecure(dns_db_t *db) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_issecure(sampledb->rbtdb));
}

static unsigned int
nodecount(dns_db_t *db) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_nodecount(sampledb->rbtdb));
}

/*
 * The database does not need to be loaded from disk or written to disk.
 * Always return ISC_TRUE.
 */
static isc_boolean_t
ispersistent(dns_db_t *db) {
    UNUSED(db);

    return (ISC_TRUE);
}

static void
overmem(dns_db_t *db, isc_boolean_t over) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_overmem(sampledb->rbtdb, over);
}

static void
settask(dns_db_t *db, isc_task_t *task) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_settask(sampledb->rbtdb, task);
}

static isc_result_t
getoriginnode(dns_db_t *db, dns_dbnode_t **nodep) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_getoriginnode(sampledb->rbtdb, nodep));
}

static void
transfernode(dns_db_t *db, dns_dbnode_t **sourcep, dns_dbnode_t **targetp) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_transfernode(sampledb->rbtdb, sourcep, targetp);

}

static isc_result_t
getnsec3parameters(dns_db_t *db, dns_dbversion_t *version,
           dns_hash_t *hash, isc_uint8_t *flags,
           isc_uint16_t *iterations,
           unsigned char *salt, size_t *salt_length)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_getnsec3parameters(sampledb->rbtdb, version,
                      hash, flags, iterations,
                      salt, salt_length));

}

static isc_result_t
findnsec3node(dns_db_t *db, dns_name_t *name, isc_boolean_t create,
          dns_dbnode_t **nodep)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_findnsec3node(sampledb->rbtdb, name, create, nodep));
}

static isc_result_t
setsigningtime(dns_db_t *db, dns_rdataset_t *rdataset, isc_stdtime_t resign) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_setsigningtime(sampledb->rbtdb, rdataset, resign));
}

static isc_result_t
getsigningtime(dns_db_t *db, dns_rdataset_t *rdataset, dns_name_t *name) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_getsigningtime(sampledb->rbtdb, rdataset, name));
}

static void
resigned(dns_db_t *db, dns_rdataset_t *rdataset, dns_dbversion_t *version) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_resigned(sampledb->rbtdb, rdataset, version);
}

static isc_boolean_t
isdnssec(dns_db_t *db) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_isdnssec(sampledb->rbtdb));
}

static dns_stats_t *
getrrsetstats(dns_db_t *db) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_getrrsetstats(sampledb->rbtdb));

}

static void
rpz_attach(dns_db_t *db, dns_rpz_zones_t *rpzs, dns_rpz_num_t rpz_num) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    dns_db_rpz_attach(sampledb->rbtdb, rpzs, rpz_num);
}

static isc_result_t
rpz_ready(dns_db_t *db) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_rpz_ready(sampledb->rbtdb));
}

static isc_result_t
findnodeext(dns_db_t *db, dns_name_t *name,
        isc_boolean_t create, dns_clientinfomethods_t *methods,
        dns_clientinfo_t *clientinfo, dns_dbnode_t **nodep)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_findnodeext(sampledb->rbtdb, name, create,
                   methods, clientinfo, nodep));
}

static isc_result_t
findext(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_clientinfomethods_t *methods, dns_clientinfo_t *clientinfo,
    dns_rdataset_t *rdataset, dns_rdataset_t *sigrdataset)
{
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_findext(sampledb->rbtdb, name, version, type,
                   options, now, nodep, foundname, methods,
                   clientinfo, rdataset, sigrdataset));
}

static isc_result_t
setcachestats(dns_db_t *db, isc_stats_t *stats) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_setcachestats(sampledb->rbtdb, stats));
}

static size_t
hashsize(dns_db_t *db) {
    sampledb_t *sampledb = (sampledb_t *) db;

    REQUIRE(VALID_SAMPLEDB(sampledb));

    return (dns_db_hashsize(sampledb->rbtdb));
}

/*
 * DB interface definition. Database driver uses this structure to
 * determine which implementation of dns_db_*() function to call.
 */
static dns_dbmethods_t sampledb_methods = {
    attach,
    detach,
    beginload,
    endload,
    serialize,
    dump,
    currentversion,
    newversion,
    attachversion,
    closeversion,
    findnode,
    find,
    findzonecut,
    attachnode,
    detachnode,
    expirenode,
    printnode,
    createiterator,
    findrdataset,
    allrdatasets,
    addrdataset,
    subtractrdataset,
    deleterdataset,
    issecure,
    nodecount,
    ispersistent,
    overmem,
    settask,
    getoriginnode,
    transfernode,
    getnsec3parameters,
    findnsec3node,
    setsigningtime,
    getsigningtime,
    resigned,
    isdnssec,
    getrrsetstats,
    rpz_attach,
    rpz_ready,
    findnodeext,
    findext,
    setcachestats,
    hashsize,
    NULL,
    NULL,
};

/* Auxiliary driver functions. */

/*
 * Auxiliary functions add_*() create minimal database which can be loaded.
 * This is necessary because this driver create empty 'fake' zone which
 * is not loaded from disk so there is no way for user to supply SOA, NS and A
 * records.
 *
 * Following functions were copied from BIND 9.10.2rc1 named/server.c,
 * credit goes to ISC.
 */
static isc_result_t
add_soa(dns_db_t *db, dns_dbversion_t *version, dns_name_t *name,
    dns_name_t *origin, dns_name_t *contact)
{
    dns_dbnode_t *node = NULL;
    dns_rdata_t rdata = DNS_RDATA_INIT;
    dns_rdatalist_t rdatalist;
    dns_rdataset_t rdataset;
    isc_result_t result;
    unsigned char buf[DNS_SOA_BUFFERSIZE];

    dns_rdataset_init(&rdataset);
    dns_rdatalist_init(&rdatalist);
    CHECK(dns_soa_buildrdata(origin, contact, dns_db_class(db),
                 0, 28800, 7200, 604800, 86400, buf, &rdata));
    rdatalist.type = rdata.type;
    rdatalist.covers = 0;
    rdatalist.rdclass = rdata.rdclass;
    rdatalist.ttl = 86400;
    ISC_LIST_APPEND(rdatalist.rdata, &rdata, link);
    CHECK(dns_rdatalist_tordataset(&rdatalist, &rdataset));
    CHECK(dns_db_findnode(db, name, ISC_TRUE, &node));
    CHECK(dns_db_addrdataset(db, node, version, 0, &rdataset, 0, NULL));
 cleanup:
    if (node != NULL)
        dns_db_detachnode(db, &node);
    return (result);
}


static isc_result_t
add_ns(dns_db_t *db, dns_dbversion_t *version, dns_name_t *name,
       dns_name_t *nsname)
{
    dns_dbnode_t *node = NULL;
    dns_rdata_ns_t ns;
    dns_rdata_t rdata = DNS_RDATA_INIT;
    dns_rdatalist_t rdatalist;
    dns_rdataset_t rdataset;
    isc_result_t result;
    isc_buffer_t b;
    unsigned char buf[DNS_NAME_MAXWIRE];

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

    dns_rdataset_init(&rdataset);
    dns_rdatalist_init(&rdatalist);
    ns.common.rdtype = dns_rdatatype_ns;
    ns.common.rdclass = dns_db_class(db);
    ns.mctx = NULL;
    dns_name_init(&ns.name, NULL);
    dns_name_clone(nsname, &ns.name);
    CHECK(dns_rdata_fromstruct(&rdata, dns_db_class(db), dns_rdatatype_ns,
                   &ns, &b));
    rdatalist.type = rdata.type;
    rdatalist.covers = 0;
    rdatalist.rdclass = rdata.rdclass;
    rdatalist.ttl = 86400;
    ISC_LIST_APPEND(rdatalist.rdata, &rdata, link);
    CHECK(dns_rdatalist_tordataset(&rdatalist, &rdataset));
    CHECK(dns_db_findnode(db, name, ISC_TRUE, &node));
    CHECK(dns_db_addrdataset(db, node, version, 0, &rdataset, 0, NULL));
 cleanup:
    if (node != NULL)
        dns_db_detachnode(db, &node);
    return (result);
}

static isc_result_t
add_a(dns_db_t *db, dns_dbversion_t *version, dns_name_t *name,
      struct in_addr addr)
{
    dns_dbnode_t *node = NULL;
    dns_rdata_in_a_t a;
    dns_rdata_t rdata = DNS_RDATA_INIT;
    dns_rdatalist_t rdatalist;
    dns_rdataset_t rdataset;
    isc_result_t result;
    isc_buffer_t b;
    unsigned char buf[DNS_NAME_MAXWIRE];

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

    dns_rdataset_init(&rdataset);
    dns_rdatalist_init(&rdatalist);
    a.common.rdtype = dns_rdatatype_a;
    a.common.rdclass = dns_db_class(db);
    a.in_addr = addr;
    CHECK(dns_rdata_fromstruct(&rdata, dns_db_class(db), dns_rdatatype_a,
                   &a, &b));
    rdatalist.type = rdata.type;
    rdatalist.covers = 0;
    rdatalist.rdclass = rdata.rdclass;
    rdatalist.ttl = 86400;
    ISC_LIST_APPEND(rdatalist.rdata, &rdata, link);
    CHECK(dns_rdatalist_tordataset(&rdatalist, &rdataset));
    CHECK(dns_db_findnode(db, name, ISC_TRUE, &node));
    CHECK(dns_db_addrdataset(db, node, version, 0, &rdataset, 0, NULL));
 cleanup:
    if (node != NULL)
        dns_db_detachnode(db, &node);
    return (result);
}

/*
 * Driver-specific implementation of dns_db_create().
 *
 * @param[in] argv      Database-specific parameters from dns_db_create().
 * @param[in] driverarg Driver-specific parameter from dns_db_register().
 */
isc_result_t
create_db(isc_mem_t *mctx, dns_name_t *origin, dns_dbtype_t type,
      dns_rdataclass_t rdclass, unsigned int argc, char *argv[],
      void *driverarg, dns_db_t **dbp)
{
    sampledb_t *sampledb = NULL;
    isc_result_t result;
    dns_dbversion_t *version = NULL;
    struct in_addr a_addr;

    REQUIRE(type == dns_dbtype_zone);
    REQUIRE(rdclass == dns_rdataclass_in);
    REQUIRE(argc == 0);
    REQUIRE(argv != NULL);
    REQUIRE(driverarg != NULL); /* pointer to driver instance */
    REQUIRE(dbp != NULL && *dbp == NULL);

    UNUSED(driverarg); /* no driver-specific configuration */

    a_addr.s_addr = 0x0100007fU;

    CHECKED_MEM_GET_PTR(mctx, sampledb);
    ZERO_PTR(sampledb);

    isc_mem_attach(mctx, &sampledb->common.mctx);
    dns_name_init(&sampledb->common.origin, NULL);
    isc_ondestroy_init(&sampledb->common.ondest);

    sampledb->common.magic = DNS_DB_MAGIC;
    sampledb->common.impmagic = SAMPLEDB_MAGIC;

    sampledb->common.methods = &sampledb_methods;
    sampledb->common.attributes = 0;
    sampledb->common.rdclass = rdclass;

    CHECK(dns_name_dupwithoffsets(origin, mctx, &sampledb->common.origin));

    CHECK(isc_refcount_init(&sampledb->refs, 1));

    /* Translate instance name to instance pointer. */
    sampledb->inst = driverarg;

    /* Create internal instance of RBT DB implementation from BIND. */
    CHECK(dns_db_create(mctx, "rbt", origin, dns_dbtype_zone,
                dns_rdataclass_in, 0, NULL, &sampledb->rbtdb));

    /* Create fake SOA, NS, and A records to make database loadable. */
    CHECK(dns_db_newversion(sampledb->rbtdb, &version));
    CHECK(add_soa(sampledb->rbtdb, version, origin, origin, origin));
    CHECK(add_ns(sampledb->rbtdb, version, origin, origin));
    CHECK(add_a(sampledb->rbtdb, version, origin, a_addr));
    dns_db_closeversion(sampledb->rbtdb, &version, ISC_TRUE);

    *dbp = (dns_db_t *)sampledb;

    return (ISC_R_SUCCESS);

cleanup:
    if (sampledb != NULL) {
        if (dns_name_dynamic(&sampledb->common.origin))
            dns_name_free(&sampledb->common.origin, mctx);

        isc_mem_putanddetach(&sampledb->common.mctx, sampledb,
                     sizeof(*sampledb));
    }

    return (result);
}