update.c

/*
 * Copyright (C) 2004-2006  Internet Systems Consortium, Inc. ("ISC")
 * Copyright (C) 1999-2003  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: update.c,v 1.130 2006/12/04 01:52:45 marka Exp $ */

#include <config.h>

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

#include <dns/db.h>
#include <dns/dbiterator.h>
#include <dns/diff.h>
#include <dns/dnssec.h>
#include <dns/events.h>
#include <dns/fixedname.h>
#include <dns/journal.h>
#include <dns/keyvalues.h>
#include <dns/message.h>
#include <dns/nsec.h>
#include <dns/rdataclass.h>
#include <dns/rdataset.h>
#include <dns/rdatasetiter.h>
#include <dns/rdatastruct.h>
#include <dns/rdatatype.h>
#include <dns/soa.h>
#include <dns/ssu.h>
#include <dns/view.h>
#include <dns/zone.h>
#include <dns/zt.h>

#include <named/client.h>
#include <named/log.h>
#include <named/update.h>

/*! \file
 * \brief
 * This module implements dynamic update as in RFC2136.
 */

/*
 *  XXX TODO:
 * - document strict minimality
 */

/**************************************************************************/

/*%
 * Log level for tracing dynamic update protocol requests.
 */
#define LOGLEVEL_PROTOCOL	ISC_LOG_INFO

/*%
 * Log level for low-level debug tracing.
 */
#define LOGLEVEL_DEBUG		ISC_LOG_DEBUG(8)

/*%
 * Check an operation for failure.  These macros all assume that
 * the function using them has a 'result' variable and a 'failure'
 * label.
 */
#define CHECK(op) \
	do { result = (op); \
		if (result != ISC_R_SUCCESS) goto failure; \
	} while (0)

/*%
 * Fail unconditionally with result 'code', which must not
 * be ISC_R_SUCCESS.  The reason for failure presumably has
 * been logged already.
 *
 * The test against ISC_R_SUCCESS is there to keep the Solaris compiler
 * from complaining about "end-of-loop code not reached".
 */

#define FAIL(code) \
	do {							\
		result = (code);				\
		if (result != ISC_R_SUCCESS) goto failure;	\
	} while (0)

/*%
 * Fail unconditionally and log as a client error.
 * The test against ISC_R_SUCCESS is there to keep the Solaris compiler
 * from complaining about "end-of-loop code not reached".
 */
#define FAILC(code, msg) \
	do {							\
		const char *_what = "failed";			\
		result = (code);				\
		switch (result) {				\
		case DNS_R_NXDOMAIN:				\
		case DNS_R_YXDOMAIN:				\
		case DNS_R_YXRRSET:				\
		case DNS_R_NXRRSET:				\
			_what = "unsuccessful";			\
		}						\
		update_log(client, zone, LOGLEVEL_PROTOCOL,	\
			   "update %s: %s (%s)", _what,		\
			   msg, isc_result_totext(result));	\
		if (result != ISC_R_SUCCESS) goto failure;	\
	} while (0)

#define FAILN(code, name, msg) \
	do {								\
		const char *_what = "failed";				\
		result = (code);					\
		switch (result) {					\
		case DNS_R_NXDOMAIN:					\
		case DNS_R_YXDOMAIN:					\
		case DNS_R_YXRRSET:					\
		case DNS_R_NXRRSET:					\
			_what = "unsuccessful";				\
		}							\
		if (isc_log_wouldlog(ns_g_lctx, LOGLEVEL_PROTOCOL)) {	\
			char _nbuf[DNS_NAME_FORMATSIZE];		\
			dns_name_format(name, _nbuf, sizeof(_nbuf));	\
			update_log(client, zone, LOGLEVEL_PROTOCOL,	\
				   "update %s: %s: %s (%s)", _what, _nbuf, \
				   msg, isc_result_totext(result));	\
		}							\
		if (result != ISC_R_SUCCESS) goto failure;		\
	} while (0)

#define FAILNT(code, name, type, msg) \
	do {								\
		const char *_what = "failed";				\
		result = (code);					\
		switch (result) {					\
		case DNS_R_NXDOMAIN:					\
		case DNS_R_YXDOMAIN:					\
		case DNS_R_YXRRSET:					\
		case DNS_R_NXRRSET:					\
			_what = "unsuccessful";				\
		}							\
		if (isc_log_wouldlog(ns_g_lctx, LOGLEVEL_PROTOCOL)) {	\
			char _nbuf[DNS_NAME_FORMATSIZE];		\
			char _tbuf[DNS_RDATATYPE_FORMATSIZE];		\
			dns_name_format(name, _nbuf, sizeof(_nbuf));	\
			dns_rdatatype_format(type, _tbuf, sizeof(_tbuf)); \
			update_log(client, zone, LOGLEVEL_PROTOCOL,	\
				   "update %s: %s/%s: %s (%s)",		\
				   _what, _nbuf, _tbuf, msg,		\
				   isc_result_totext(result));		\
		}							\
		if (result != ISC_R_SUCCESS) goto failure;		\
	} while (0)
/*%
 * Fail unconditionally and log as a server error.
 * The test against ISC_R_SUCCESS is there to keep the Solaris compiler
 * from complaining about "end-of-loop code not reached".
 */
#define FAILS(code, msg) \
	do {							\
		result = (code);				\
		update_log(client, zone, LOGLEVEL_PROTOCOL,	\
			   "error: %s: %s",			\
			   msg, isc_result_totext(result));	\
		if (result != ISC_R_SUCCESS) goto failure;	\
	} while (0)

/**************************************************************************/

typedef struct rr rr_t;

struct rr {
	/* dns_name_t name; */
	isc_uint32_t		ttl;
	dns_rdata_t		rdata;
};

typedef struct update_event update_event_t;

struct update_event {
	ISC_EVENT_COMMON(update_event_t);
	dns_zone_t		*zone;
	isc_result_t		result;
	dns_message_t		*answer;
};

/**************************************************************************/
/*
 * Forward declarations.
 */

static void update_action(isc_task_t *task, isc_event_t *event);
static void updatedone_action(isc_task_t *task, isc_event_t *event);
static isc_result_t send_forward_event(ns_client_t *client, dns_zone_t *zone);
static void forward_done(isc_task_t *task, isc_event_t *event);

/**************************************************************************/

static void
update_log(ns_client_t *client, dns_zone_t *zone,
	   int level, const char *fmt, ...) ISC_FORMAT_PRINTF(4, 5);

static void
update_log(ns_client_t *client, dns_zone_t *zone,
	   int level, const char *fmt, ...)
{
	va_list ap;
	char message[4096];
	char namebuf[DNS_NAME_FORMATSIZE];
	char classbuf[DNS_RDATACLASS_FORMATSIZE];

	if (client == NULL || zone == NULL)
		return;

	if (isc_log_wouldlog(ns_g_lctx, level) == ISC_FALSE)
		return;

	dns_name_format(dns_zone_getorigin(zone), namebuf,
			sizeof(namebuf));
	dns_rdataclass_format(dns_zone_getclass(zone), classbuf,
			      sizeof(classbuf));

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

	ns_client_log(client, NS_LOGCATEGORY_UPDATE, NS_LOGMODULE_UPDATE,
		      level, "updating zone '%s/%s': %s",
		      namebuf, classbuf, message);
}

static isc_result_t
checkupdateacl(ns_client_t *client, dns_acl_t *acl, const char *message,
	       dns_name_t *zonename, isc_boolean_t slave)
{
	char namebuf[DNS_NAME_FORMATSIZE];
	char classbuf[DNS_RDATACLASS_FORMATSIZE];
	int level = ISC_LOG_ERROR;
	const char *msg = "denied";
	isc_result_t result;

	if (slave && acl == NULL) {
		result = DNS_R_NOTIMP;
		level = ISC_LOG_DEBUG(3);
		msg = "disabled";
	} else
		result = ns_client_checkaclsilent(client, acl, ISC_FALSE);

	if (result == ISC_R_SUCCESS) {
		level = ISC_LOG_DEBUG(3);
		msg = "approved";
	}

	if (client->signer != NULL) {
		dns_name_format(client->signer, namebuf, sizeof(namebuf));
		ns_client_log(client, NS_LOGCATEGORY_UPDATE_SECURITY,
			      NS_LOGMODULE_UPDATE, ISC_LOG_INFO,
			      "signer \"%s\" %s", namebuf, msg);
	}

	dns_name_format(zonename, namebuf, sizeof(namebuf));
	dns_rdataclass_format(client->view->rdclass, classbuf,
			      sizeof(classbuf));

	ns_client_log(client, NS_LOGCATEGORY_UPDATE_SECURITY,
		      NS_LOGMODULE_UPDATE, level, "%s '%s/%s' %s",
		      message, namebuf, classbuf, msg);
	return (result);
}

/*%
 * Update a single RR in version 'ver' of 'db' and log the
 * update in 'diff'.
 *
 * Ensures:
 * \li	'*tuple' == NULL.  Either the tuple is freed, or its
 *	ownership has been transferred to the diff.
 */
static isc_result_t
do_one_tuple(dns_difftuple_t **tuple, dns_db_t *db, dns_dbversion_t *ver,
	     dns_diff_t *diff)
{
	dns_diff_t temp_diff;
	isc_result_t result;

	/*
	 * Create a singleton diff.
	 */
	dns_diff_init(diff->mctx, &temp_diff);
	ISC_LIST_APPEND(temp_diff.tuples, *tuple, link);

	/*
	 * Apply it to the database.
	 */
	result = dns_diff_apply(&temp_diff, db, ver);
	ISC_LIST_UNLINK(temp_diff.tuples, *tuple, link);
	if (result != ISC_R_SUCCESS) {
		dns_difftuple_free(tuple);
		return (result);
	}

	/*
	 * Merge it into the current pending journal entry.
	 */
	dns_diff_appendminimal(diff, tuple);

	/*
	 * Do not clear temp_diff.
	 */
	return (ISC_R_SUCCESS);
}

/*%
 * Perform the updates in 'updates' in version 'ver' of 'db' and log the
 * update in 'diff'.
 *
 * Ensures:
 * \li	'updates' is empty.
 */
static isc_result_t
do_diff(dns_diff_t *updates, dns_db_t *db, dns_dbversion_t *ver,
	dns_diff_t *diff)
{
	isc_result_t result;
	while (! ISC_LIST_EMPTY(updates->tuples)) {
		dns_difftuple_t *t = ISC_LIST_HEAD(updates->tuples);
		ISC_LIST_UNLINK(updates->tuples, t, link);
		CHECK(do_one_tuple(&t, db, ver, diff));
	}
	return (ISC_R_SUCCESS);

 failure:
	dns_diff_clear(diff);
	return (result);
}

static isc_result_t
update_one_rr(dns_db_t *db, dns_dbversion_t *ver, dns_diff_t *diff,
	      dns_diffop_t op, dns_name_t *name, dns_ttl_t ttl,
	      dns_rdata_t *rdata)
{
	dns_difftuple_t *tuple = NULL;
	isc_result_t result;
	result = dns_difftuple_create(diff->mctx, op,
				      name, ttl, rdata, &tuple);
	if (result != ISC_R_SUCCESS)
		return (result);
	return (do_one_tuple(&tuple, db, ver, diff));
}

/**************************************************************************/
/*
 * Callback-style iteration over rdatasets and rdatas.
 *
 * foreach_rrset() can be used to iterate over the RRsets
 * of a name and call a callback function with each
 * one.  Similarly, foreach_rr() can be used to iterate
 * over the individual RRs at name, optionally restricted
 * to RRs of a given type.
 *
 * The callback functions are called "actions" and take
 * two arguments: a void pointer for passing arbitrary
 * context information, and a pointer to the current RRset
 * or RR.  By convention, their names end in "_action".
 */

/*
 * XXXRTH  We might want to make this public somewhere in libdns.
 */

/*%
 * Function type for foreach_rrset() iterator actions.
 */
typedef isc_result_t rrset_func(void *data, dns_rdataset_t *rrset);

/*%
 * Function type for foreach_rr() iterator actions.
 */
typedef isc_result_t rr_func(void *data, rr_t *rr);

/*%
 * Internal context struct for foreach_node_rr().
 */
typedef struct {
	rr_func *	rr_action;
	void *		rr_action_data;
} foreach_node_rr_ctx_t;

/*%
 * Internal helper function for foreach_node_rr().
 */
static isc_result_t
foreach_node_rr_action(void *data, dns_rdataset_t *rdataset) {
	isc_result_t result;
	foreach_node_rr_ctx_t *ctx = data;
	for (result = dns_rdataset_first(rdataset);
	     result == ISC_R_SUCCESS;
	     result = dns_rdataset_next(rdataset))
	{
		rr_t rr = { 0, DNS_RDATA_INIT };
		
		dns_rdataset_current(rdataset, &rr.rdata);
		rr.ttl = rdataset->ttl;
		result = (*ctx->rr_action)(ctx->rr_action_data, &rr);
		if (result != ISC_R_SUCCESS)
			return (result);
	}
	if (result != ISC_R_NOMORE)
		return (result);
	return (ISC_R_SUCCESS);
}

/*%
 * For each rdataset of 'name' in 'ver' of 'db', call 'action'
 * with the rdataset and 'action_data' as arguments.  If the name
 * does not exist, do nothing.
 *
 * If 'action' returns an error, abort iteration and return the error.
 */
static isc_result_t
foreach_rrset(dns_db_t *db, dns_dbversion_t *ver, dns_name_t *name,
	      rrset_func *action, void *action_data)
{
	isc_result_t result;
	dns_dbnode_t *node;
	dns_rdatasetiter_t *iter;

	node = NULL;
	result = dns_db_findnode(db, name, ISC_FALSE, &node);
	if (result == ISC_R_NOTFOUND)
		return (ISC_R_SUCCESS);
	if (result != ISC_R_SUCCESS)
		return (result);

	iter = NULL;
	result = dns_db_allrdatasets(db, node, ver,
				     (isc_stdtime_t) 0, &iter);
	if (result != ISC_R_SUCCESS)
		goto cleanup_node;

	for (result = dns_rdatasetiter_first(iter);
	     result == ISC_R_SUCCESS;
	     result = dns_rdatasetiter_next(iter))
	{
		dns_rdataset_t rdataset;

		dns_rdataset_init(&rdataset);
		dns_rdatasetiter_current(iter, &rdataset);

		result = (*action)(action_data, &rdataset);

		dns_rdataset_disassociate(&rdataset);
		if (result != ISC_R_SUCCESS)
			goto cleanup_iterator;
	}
	if (result == ISC_R_NOMORE)
		result = ISC_R_SUCCESS;

 cleanup_iterator:
	dns_rdatasetiter_destroy(&iter);

 cleanup_node:
	dns_db_detachnode(db, &node);

	return (result);
}

/*%
 * For each RR of 'name' in 'ver' of 'db', call 'action'
 * with the RR and 'action_data' as arguments.  If the name
 * does not exist, do nothing.
 *
 * If 'action' returns an error, abort iteration
 * and return the error.
 */
static isc_result_t
foreach_node_rr(dns_db_t *db, dns_dbversion_t *ver, dns_name_t *name,
		rr_func *rr_action, void *rr_action_data)
{
	foreach_node_rr_ctx_t ctx;
	ctx.rr_action = rr_action;
	ctx.rr_action_data = rr_action_data;
	return (foreach_rrset(db, ver, name,
			      foreach_node_rr_action, &ctx));
}


/*%
 * For each of the RRs specified by 'db', 'ver', 'name', 'type',
 * (which can be dns_rdatatype_any to match any type), and 'covers', call
 * 'action' with the RR and 'action_data' as arguments. If the name
 * does not exist, or if no RRset of the given type exists at the name,
 * do nothing.
 *
 * If 'action' returns an error, abort iteration and return the error.
 */
static isc_result_t
foreach_rr(dns_db_t *db, dns_dbversion_t *ver, dns_name_t *name,
	   dns_rdatatype_t type, dns_rdatatype_t covers, rr_func *rr_action,
	   void *rr_action_data)
{

	isc_result_t result;
	dns_dbnode_t *node;
	dns_rdataset_t rdataset;

	if (type == dns_rdatatype_any)
		return (foreach_node_rr(db, ver, name,
					rr_action, rr_action_data));

	node = NULL;
	result = dns_db_findnode(db, name, ISC_FALSE, &node);
	if (result == ISC_R_NOTFOUND)
		return (ISC_R_SUCCESS);
	if (result != ISC_R_SUCCESS)
		return (result);

	dns_rdataset_init(&rdataset);
	result = dns_db_findrdataset(db, node, ver, type, covers,
				     (isc_stdtime_t) 0, &rdataset, NULL);
	if (result == ISC_R_NOTFOUND) {
		result = ISC_R_SUCCESS;
		goto cleanup_node;
	}
	if (result != ISC_R_SUCCESS)
		goto cleanup_node;

	for (result = dns_rdataset_first(&rdataset);
	     result == ISC_R_SUCCESS;
	     result = dns_rdataset_next(&rdataset))
	{
		rr_t rr = { 0, DNS_RDATA_INIT };
		dns_rdataset_current(&rdataset, &rr.rdata);
		rr.ttl = rdataset.ttl;
		result = (*rr_action)(rr_action_data, &rr);
		if (result != ISC_R_SUCCESS)
			goto cleanup_rdataset;
	}
	if (result != ISC_R_NOMORE)
		goto cleanup_rdataset;
	result = ISC_R_SUCCESS;

 cleanup_rdataset:
	dns_rdataset_disassociate(&rdataset);
 cleanup_node:
	dns_db_detachnode(db, &node);

	return (result);
}

/**************************************************************************/
/*
 * Various tests on the database contents (for prerequisites, etc).
 */

/*%
 * Function type for predicate functions that compare a database RR 'db_rr'
 * against an update RR 'update_rr'.
 */
typedef isc_boolean_t rr_predicate(dns_rdata_t *update_rr, dns_rdata_t *db_rr);

/*%
 * Helper function for rrset_exists().
 */
static isc_result_t
rrset_exists_action(void *data, rr_t *rr) {
	UNUSED(data);
	UNUSED(rr);
	return (ISC_R_EXISTS);
}

/*%
 * Utility macro for RR existence checking functions.
 *
 * If the variable 'result' has the value ISC_R_EXISTS or
 * ISC_R_SUCCESS, set *exists to ISC_TRUE or ISC_FALSE,
 * respectively, and return success.
 *
 * If 'result' has any other value, there was a failure.
 * Return the failure result code and do not set *exists.
 *
 * This would be more readable as "do { if ... } while(0)",
 * but that form generates tons of warnings on Solaris 2.6.
 */
#define RETURN_EXISTENCE_FLAG				\
	return ((result == ISC_R_EXISTS) ?		\
		(*exists = ISC_TRUE, ISC_R_SUCCESS) :	\
		((result == ISC_R_SUCCESS) ?		\
		 (*exists = ISC_FALSE, ISC_R_SUCCESS) :	\
		 result))

/*%
 * Set '*exists' to true iff an rrset of the given type exists,
 * to false otherwise.
 */
static isc_result_t
rrset_exists(dns_db_t *db, dns_dbversion_t *ver, dns_name_t *name,
	     dns_rdatatype_t type, dns_rdatatype_t covers,
	     isc_boolean_t *exists)
{
	isc_result_t result;
	result = foreach_rr(db, ver, name, type, covers,
			    rrset_exists_action, NULL);
	RETURN_EXISTENCE_FLAG;
}

/*%
 * Helper function for cname_incompatible_rrset_exists.
 */
static isc_result_t
cname_compatibility_action(void *data, dns_rdataset_t *rrset) {
	UNUSED(data);
	if (rrset->type != dns_rdatatype_cname &&
	    ! dns_rdatatype_isdnssec(rrset->type))
		return (ISC_R_EXISTS);
	return (ISC_R_SUCCESS);
}

/*%
 * Check whether there is an rrset incompatible with adding a CNAME RR,
 * i.e., anything but another CNAME (which can be replaced) or a
 * DNSSEC RR (which can coexist).
 *
 * If such an incompatible rrset exists, set '*exists' to ISC_TRUE.
 * Otherwise, set it to ISC_FALSE.
 */
static isc_result_t
cname_incompatible_rrset_exists(dns_db_t *db, dns_dbversion_t *ver,
				dns_name_t *name, isc_boolean_t *exists) {
	isc_result_t result;
	result = foreach_rrset(db, ver, name,
			       cname_compatibility_action, NULL);
	RETURN_EXISTENCE_FLAG;
}

/*%
 * Helper function for rr_count().
 */
static isc_result_t
count_rr_action(void *data, rr_t *rr) {
	int *countp = data;
	UNUSED(rr);
	(*countp)++;
	return (ISC_R_SUCCESS);
}

/*%
 * Count the number of RRs of 'type' belonging to 'name' in 'ver' of 'db'.
 */
static isc_result_t
rr_count(dns_db_t *db, dns_dbversion_t *ver, dns_name_t *name,
	 dns_rdatatype_t type, dns_rdatatype_t covers, int *countp)
{
	*countp = 0;
	return (foreach_rr(db, ver, name, type, covers,
			   count_rr_action, countp));
}

/*%
 * Context struct and helper function for name_exists().
 */

static isc_result_t
name_exists_action(void *data, dns_rdataset_t *rrset) {
	UNUSED(data);
	UNUSED(rrset);
	return (ISC_R_EXISTS);
}

/*%
 * Set '*exists' to true iff the given name exists, to false otherwise.
 */
static isc_result_t
name_exists(dns_db_t *db, dns_dbversion_t *ver, dns_name_t *name,
	    isc_boolean_t *exists)
{
	isc_result_t result;
	result = foreach_rrset(db, ver, name,
			       name_exists_action, NULL);
	RETURN_EXISTENCE_FLAG;
}

typedef struct {
	dns_name_t *name;
	dns_name_t *signer;
	dns_ssutable_t *table;
} ssu_check_t;

static isc_result_t
ssu_checkrule(void *data, dns_rdataset_t *rrset) {
	ssu_check_t *ssuinfo = data;
	isc_boolean_t result;

	/*
	 * If we're deleting all records, it's ok to delete RRSIG and NSEC even
	 * if we're normally not allowed to.
	 */
	if (rrset->type == dns_rdatatype_rrsig ||
	    rrset->type == dns_rdatatype_nsec)
		return (ISC_R_SUCCESS);
	result = dns_ssutable_checkrules(ssuinfo->table, ssuinfo->signer,
					 ssuinfo->name, rrset->type);
	return (result == ISC_TRUE ? ISC_R_SUCCESS : ISC_R_FAILURE);
}

static isc_boolean_t
ssu_checkall(dns_db_t *db, dns_dbversion_t *ver, dns_name_t *name,
	     dns_ssutable_t *ssutable, dns_name_t *signer)
{
	isc_result_t result;
	ssu_check_t ssuinfo;

	ssuinfo.name = name;
	ssuinfo.table = ssutable;
	ssuinfo.signer = signer;
	result = foreach_rrset(db, ver, name, ssu_checkrule, &ssuinfo);
	return (ISC_TF(result == ISC_R_SUCCESS));
}

/**************************************************************************/
/*
 * Checking of "RRset exists (value dependent)" prerequisites.
 *
 * In the RFC2136 section 3.2.5, this is the pseudocode involving
 * a variable called "temp", a mapping of <name, type> tuples to rrsets.
 *
 * Here, we represent the "temp" data structure as (non-minimial) "dns_diff_t"
 * where each typle has op==DNS_DIFFOP_EXISTS.
 */


/*%
 * Append a tuple asserting the existence of the RR with
 * 'name' and 'rdata' to 'diff'.
 */
static isc_result_t
temp_append(dns_diff_t *diff, dns_name_t *name, dns_rdata_t *rdata) {
	isc_result_t result;
	dns_difftuple_t *tuple = NULL;

	REQUIRE(DNS_DIFF_VALID(diff));
	CHECK(dns_difftuple_create(diff->mctx, DNS_DIFFOP_EXISTS,
				   name, 0, rdata, &tuple));
	ISC_LIST_APPEND(diff->tuples, tuple, link);
 failure:
	return (result);
}

/*%
 * Compare two rdatasets represented as sorted lists of tuples.
 * All list elements must have the same owner name and type.
 * Return ISC_R_SUCCESS if the rdatasets are equal, rcode(dns_rcode_nxrrset)
 * if not.
 */
static isc_result_t
temp_check_rrset(dns_difftuple_t *a, dns_difftuple_t *b) {
	for (;;) {
		if (a == NULL || b == NULL)
			break;
		INSIST(a->op == DNS_DIFFOP_EXISTS &&
		       b->op == DNS_DIFFOP_EXISTS);
		INSIST(a->rdata.type == b->rdata.type);
		INSIST(dns_name_equal(&a->name, &b->name));
		if (dns_rdata_compare(&a->rdata, &b->rdata) != 0)
			return (DNS_R_NXRRSET);
		a = ISC_LIST_NEXT(a, link);
		b = ISC_LIST_NEXT(b, link);
	}
	if (a != NULL || b != NULL)
		return (DNS_R_NXRRSET);
	return (ISC_R_SUCCESS);
}

/*%
 * A comparison function defining the sorting order for the entries
 * in the "temp" data structure.  The major sort key is the owner name,
 * followed by the type and rdata.
 */
static int
temp_order(const void *av, const void *bv) {
	dns_difftuple_t const * const *ap = av;
	dns_difftuple_t const * const *bp = bv;
	dns_difftuple_t const *a = *ap;
	dns_difftuple_t const *b = *bp;
	int r;
	r = dns_name_compare(&a->name, &b->name);
	if (r != 0)
		return (r);
	r = (b->rdata.type - a->rdata.type);
	if (r != 0)
		return (r);
	r = dns_rdata_compare(&a->rdata, &b->rdata);
	return (r);
}

/*%
 * Check the "RRset exists (value dependent)" prerequisite information
 * in 'temp' against the contents of the database 'db'.
 *
 * Return ISC_R_SUCCESS if the prerequisites are satisfied,
 * rcode(dns_rcode_nxrrset) if not.
 *
 * 'temp' must be pre-sorted.
 */

static isc_result_t
temp_check(isc_mem_t *mctx, dns_diff_t *temp, dns_db_t *db,
	   dns_dbversion_t *ver, dns_name_t *tmpname, dns_rdatatype_t *typep)
{
	isc_result_t result;
	dns_name_t *name;
	dns_dbnode_t *node;
	dns_difftuple_t *t;
	dns_diff_t trash;

	dns_diff_init(mctx, &trash);

	/*
	 * For each name and type in the prerequisites,
	 * construct a sorted rdata list of the corresponding
	 * database contents, and compare the lists.
	 */
	t = ISC_LIST_HEAD(temp->tuples);
	while (t != NULL) {
		name = &t->name;
		(void)dns_name_copy(name, tmpname, NULL);
		*typep = t->rdata.type;

		/* A new unique name begins here. */
		node = NULL;
		result = dns_db_findnode(db, name, ISC_FALSE, &node);
		if (result == ISC_R_NOTFOUND)
			return (DNS_R_NXRRSET);
		if (result != ISC_R_SUCCESS)
			return (result);

		/* A new unique type begins here. */
		while (t != NULL && dns_name_equal(&t->name, name)) {
			dns_rdatatype_t type, covers;
			dns_rdataset_t rdataset;
			dns_diff_t d_rrs; /* Database RRs with
						this name and type */
			dns_diff_t u_rrs; /* Update RRs with
						this name and type */

			*typep = type = t->rdata.type;
			if (type == dns_rdatatype_rrsig ||
			    type == dns_rdatatype_sig)
				covers = dns_rdata_covers(&t->rdata);
			else
				covers = 0;

			/*
			 * Collect all database RRs for this name and type
			 * onto d_rrs and sort them.
			 */
			dns_rdataset_init(&rdataset);
			result = dns_db_findrdataset(db, node, ver, type,
						     covers, (isc_stdtime_t) 0,
						     &rdataset, NULL);
			if (result != ISC_R_SUCCESS) {
				dns_db_detachnode(db, &node);
				return (DNS_R_NXRRSET);
			}

			dns_diff_init(mctx, &d_rrs);
			dns_diff_init(mctx, &u_rrs);

			for (result = dns_rdataset_first(&rdataset);
			     result == ISC_R_SUCCESS;
			     result = dns_rdataset_next(&rdataset))
			{
				dns_rdata_t rdata = DNS_RDATA_INIT;
				dns_rdataset_current(&rdataset, &rdata);
				result = temp_append(&d_rrs, name, &rdata);
				if (result != ISC_R_SUCCESS)
					goto failure;
			}
			if (result != ISC_R_NOMORE)
				goto failure;
			result = dns_diff_sort(&d_rrs, temp_order);
			if (result != ISC_R_SUCCESS)
				goto failure;

			/*
			 * Collect all update RRs for this name and type
			 * onto u_rrs.  No need to sort them here -
			 * they are already sorted.
			 */
			while (t != NULL &&
			       dns_name_equal(&t->name, name) &&
			       t->rdata.type == type)
			{
				dns_difftuple_t *next =
					ISC_LIST_NEXT(t, link);
				ISC_LIST_UNLINK(temp->tuples, t, link);
				ISC_LIST_APPEND(u_rrs.tuples, t, link);
				t = next;
			}

			/* Compare the two sorted lists. */
			result = temp_check_rrset(ISC_LIST_HEAD(u_rrs.tuples),
						  ISC_LIST_HEAD(d_rrs.tuples));
			if (result != ISC_R_SUCCESS)
				goto failure;

			/*
			 * We are done with the tuples, but we can't free
			 * them yet because "name" still points into one
			 * of them.  Move them on a temporary list.
			 */
			ISC_LIST_APPENDLIST(trash.tuples, u_rrs.tuples, link);
			ISC_LIST_APPENDLIST(trash.tuples, d_rrs.tuples, link);
			dns_rdataset_disassociate(&rdataset);

			continue;

		    failure:
			dns_diff_clear(&d_rrs);
			dns_diff_clear(&u_rrs);
			dns_diff_clear(&trash);
			dns_rdataset_disassociate(&rdataset);
			dns_db_detachnode(db, &node);
			return (result);
		}

		dns_db_detachnode(db, &node);
	}

	dns_diff_clear(&trash);
	return (ISC_R_SUCCESS);
<