bind/lib/dns/cache.c

/*
 * Copyright (C) 2004-2007  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.
 */

/* $Id: cache.c,v 1.77 2008/02/07 02:41:26 marka Exp $ */

/*! \file */

#include <config.h>

#include <isc/mem.h>
#include <isc/task.h>
#include <isc/time.h>
#include <isc/timer.h>
#include <isc/util.h>

#include <dns/cache.h>
#include <dns/db.h>
#include <dns/dbiterator.h>
#include <dns/events.h>
#include <dns/lib.h>
#include <dns/log.h>
#include <dns/masterdump.h>
#include <dns/rdata.h>
#include <dns/rdataset.h>
#include <dns/rdatasetiter.h>
#include <dns/result.h>

#define CACHE_MAGIC             ISC_MAGIC('$', '$', '$', '$')
#define VALID_CACHE(cache)      ISC_MAGIC_VALID(cache, CACHE_MAGIC)

/*!
 * Control incremental cleaning.
 * DNS_CACHE_MINSIZE is how many bytes is the floor for dns_cache_setcachesize().
 * See also DNS_CACHE_CLEANERINCREMENT
 */
#define DNS_CACHE_MINSIZE               2097152 /*%< Bytes.  2097152 = 2 MB */
/*!
 * Control incremental cleaning.
 * CLEANERINCREMENT is how many nodes are examined in one pass.
 * See also DNS_CACHE_MINSIZE
 */
#define DNS_CACHE_CLEANERINCREMENT      1000U   /*%< Number of nodes. */

/***
 ***    Types
 ***/

/*
 * A cache_cleaner_t encapsulsates the state of the periodic
 * cache cleaning.
 */

typedef struct cache_cleaner cache_cleaner_t;

typedef enum {
        cleaner_s_idle, /*%< Waiting for cleaning-interval to expire. */
        cleaner_s_busy, /*%< Currently cleaning. */
        cleaner_s_done  /*%< Freed enough memory after being overmem. */
} cleaner_state_t;

/*
 * Convenience macros for comprehensive assertion checking.
 */
#define CLEANER_IDLE(c) ((c)->state == cleaner_s_idle)
#define CLEANER_BUSY(c) ((c)->state == cleaner_s_busy)

/*%
 * Accesses to a cache cleaner object are synchronized through
 * task/event serialization, or locked from the cache object.
 */
struct cache_cleaner {
        isc_mutex_t     lock;
        /*%<
         * Locks overmem.  Note: never allocate memory
         * while holding this lock - that could lead to deadlock since
         * the lock is take by water() which is called from the memory
         * allocator.
         */

        dns_cache_t     *cache;
        isc_task_t      *task;
        unsigned int    cleaning_interval; /*% The cleaning-interval from
                                              named.conf, in seconds. */
        isc_timer_t     *cleaning_timer;

        unsigned int     increment;     /*% Number of names to
                                           clean in one increment */
        cleaner_state_t  state;         /*% Idle/Busy. */
        isc_boolean_t    overmem;       /*% The cache is in an overmem state. */
};

/*%
 * The actual cache object.
 */

struct dns_cache {
        /* Unlocked. */
        unsigned int            magic;
        isc_mutex_t             lock;
        isc_mutex_t             filelock;
        isc_mem_t               *mctx;

        /* Locked by 'lock'. */
        int                     references;
        int                     live_tasks;
        dns_rdataclass_t        rdclass;
        dns_db_t                *db;
        cache_cleaner_t         cleaner;
        char                    *db_type;
        int                     db_argc;
        char                    **db_argv;

        /* Locked by 'filelock'. */
        char *                  filename;
        /* Access to the on-disk cache file is also locked by 'filelock'. */

#ifdef LRU_DEBUG
#define DUMP_INTERVAL 30        /* seconds */
        isc_timer_t                    *dump_timer; /* for test */
        isc_time_t                      dump_time; /* for test */
#endif
};

/***
 ***    Functions
 ***/

static isc_result_t
cache_cleaner_init(dns_cache_t *cache, isc_taskmgr_t *taskmgr,
                   isc_timermgr_t *timermgr, cache_cleaner_t *cleaner);

static void
cleaning_timer_action(isc_task_t *task, isc_event_t *event);

static void
cleaner_shutdown_action(isc_task_t *task, isc_event_t *event);

#ifdef LRU_DEBUG
static void
timer_dump(isc_task_t *task, isc_event_t *event);
#endif

#if 0 /* This is no longer needed.  When LRU_TEST is cleaned up,
       * this should be as well.  XXXMLG */
/*%
 * Work out how many nodes can be cleaned in the time between two
 * requests to the nameserver.  Smooth the resulting number and use
 * it as a estimate for the number of nodes to be cleaned in the next
 * iteration.
 */
static void
adjust_increment(cache_cleaner_t *cleaner, unsigned int remaining,
                 isc_time_t *start)
{
        isc_time_t end;
        isc_uint64_t usecs;
        isc_uint64_t new;
        unsigned int pps = dns_pps;
        unsigned int interval;
        unsigned int names;

        /*
         * Tune for minumum of 100 packets per second (pps).
         */
        if (pps < 100)
                pps = 100;

        isc_time_now(&end);

        interval = 1000000 / pps; /* Interval between packets in usecs. */
        if (interval == 0)
                interval = 1;

        INSIST(cleaner->increment >= remaining);
        names = cleaner->increment - remaining;
        usecs = isc_time_microdiff(&end, start);

        isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE, DNS_LOGMODULE_CACHE,
                      ISC_LOG_DEBUG(1), "adjust_increment interval=%u "
                      "names=%u usec=%" ISC_PLATFORM_QUADFORMAT "u",
                      interval, names, usecs);

        if (usecs == 0) {
                /*
                 * If we cleaned all the nodes in unmeasurable time
                 * double the number of nodes to be cleaned next time.
                 */
                if (names == cleaner->increment) {
                        cleaner->increment *= 2;
                        if (cleaner->increment > DNS_CACHE_CLEANERINCREMENT)
                                cleaner->increment = DNS_CACHE_CLEANERINCREMENT;
                        isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE,
                                      DNS_LOGMODULE_CACHE, ISC_LOG_DEBUG(1),
                                      "%p:new cleaner->increment = %u\n",
                                      cleaner, cleaner->increment);
                }
                return;
        }

        new = (names * interval);
        new /= (usecs * 2);
        if (new == 0)
                new = 1;

        /* Smooth */
        new = (new + cleaner->increment * 7) / 8;

        if (new > DNS_CACHE_CLEANERINCREMENT)
                new = DNS_CACHE_CLEANERINCREMENT;

        cleaner->increment = (unsigned int)new;

        isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE, DNS_LOGMODULE_CACHE,
                      ISC_LOG_DEBUG(1), "%p:new cleaner->increment = %u\n",
                      cleaner, cleaner->increment);
}
#endif

static inline isc_result_t
cache_create_db(dns_cache_t *cache, dns_db_t **db) {
        return (dns_db_create(cache->mctx, cache->db_type, dns_rootname,
                              dns_dbtype_cache, cache->rdclass,
                              cache->db_argc, cache->db_argv, db));
}

isc_result_t
dns_cache_create(isc_mem_t *mctx, isc_taskmgr_t *taskmgr,
                 isc_timermgr_t *timermgr, dns_rdataclass_t rdclass,
                 const char *db_type, unsigned int db_argc, char **db_argv,
                 dns_cache_t **cachep)
{
        isc_result_t result;
        dns_cache_t *cache;
        int i;

        REQUIRE(cachep != NULL);
        REQUIRE(*cachep == NULL);
        REQUIRE(mctx != NULL);

        cache = isc_mem_get(mctx, sizeof(*cache));
        if (cache == NULL)
                return (ISC_R_NOMEMORY);

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

        result = isc_mutex_init(&cache->lock);
        if (result != ISC_R_SUCCESS)
                goto cleanup_mem;

        result = isc_mutex_init(&cache->filelock);
        if (result != ISC_R_SUCCESS)
                goto cleanup_lock;

        cache->references = 1;
        cache->live_tasks = 0;
        cache->rdclass = rdclass;

        cache->db_type = isc_mem_strdup(mctx, db_type);
        if (cache->db_type == NULL) {
                result = ISC_R_NOMEMORY;
                goto cleanup_filelock;
        }

        cache->db_argc = db_argc;
        if (cache->db_argc == 0)
                cache->db_argv = NULL;
        else {
                cache->db_argv = isc_mem_get(mctx,
                                             cache->db_argc * sizeof(char *));
                if (cache->db_argv == NULL) {
                        result = ISC_R_NOMEMORY;
                        goto cleanup_dbtype;
                }
                for (i = 0; i < cache->db_argc; i++)
                        cache->db_argv[i] = NULL;
                for (i = 0; i < cache->db_argc; i++) {
                        cache->db_argv[i] = isc_mem_strdup(mctx, db_argv[i]);
                        if (cache->db_argv[i] == NULL) {
                                result = ISC_R_NOMEMORY;
                                goto cleanup_dbargv;
                        }
                }
        }

        cache->db = NULL;
        result = cache_create_db(cache, &cache->db);
        if (result != ISC_R_SUCCESS)
                goto cleanup_dbargv;

        cache->filename = NULL;

        cache->magic = CACHE_MAGIC;

        result = cache_cleaner_init(cache, taskmgr, timermgr, &cache->cleaner);
        if (result != ISC_R_SUCCESS)
                goto cleanup_db;

        *cachep = cache;
        return (ISC_R_SUCCESS);

 cleanup_db:
        dns_db_detach(&cache->db);
 cleanup_dbargv:
        for (i = 0; i < cache->db_argc; i++)
                if (cache->db_argv[i] != NULL)
                        isc_mem_free(mctx, cache->db_argv[i]);
        if (cache->db_argv != NULL)
                isc_mem_put(mctx, cache->db_argv,
                            cache->db_argc * sizeof(char *));
 cleanup_dbtype:
        isc_mem_free(mctx, cache->db_type);
 cleanup_filelock:
        DESTROYLOCK(&cache->filelock);
 cleanup_lock:
        DESTROYLOCK(&cache->lock);
 cleanup_mem:
        isc_mem_put(mctx, cache, sizeof(*cache));
        isc_mem_detach(&mctx);
        return (result);
}

static void
cache_free(dns_cache_t *cache) {
        isc_mem_t *mctx;
        int i;

        REQUIRE(VALID_CACHE(cache));
        REQUIRE(cache->references == 0);

        isc_mem_setwater(cache->mctx, NULL, NULL, 0, 0);

        if (cache->cleaner.task != NULL)
                isc_task_detach(&cache->cleaner.task);

        DESTROYLOCK(&cache->cleaner.lock);

        if (cache->filename) {
                isc_mem_free(cache->mctx, cache->filename);
                cache->filename = NULL;
        }

        if (cache->db != NULL)
                dns_db_detach(&cache->db);

        if (cache->db_argv != NULL) {
                for (i = 0; i < cache->db_argc; i++)
                        if (cache->db_argv[i] != NULL)
                                isc_mem_free(cache->mctx, cache->db_argv[i]);
                isc_mem_put(cache->mctx, cache->db_argv,
                            cache->db_argc * sizeof(char *));
        }

        if (cache->db_type != NULL)
                isc_mem_free(cache->mctx, cache->db_type);

        DESTROYLOCK(&cache->lock);
        DESTROYLOCK(&cache->filelock);
        cache->magic = 0;
        mctx = cache->mctx;
        isc_mem_put(cache->mctx, cache, sizeof(*cache));
        isc_mem_detach(&mctx);
}


void
dns_cache_attach(dns_cache_t *cache, dns_cache_t **targetp) {

        REQUIRE(VALID_CACHE(cache));
        REQUIRE(targetp != NULL && *targetp == NULL);

        LOCK(&cache->lock);
        cache->references++;
        UNLOCK(&cache->lock);

        *targetp = cache;
}

void
dns_cache_detach(dns_cache_t **cachep) {
        dns_cache_t *cache;
        isc_boolean_t free_cache = ISC_FALSE;

        REQUIRE(cachep != NULL);
        cache = *cachep;
        REQUIRE(VALID_CACHE(cache));

        LOCK(&cache->lock);
        REQUIRE(cache->references > 0);
        cache->references--;
        if (cache->references == 0) {
                cache->cleaner.overmem = ISC_FALSE;
                free_cache = ISC_TRUE;
        }

        *cachep = NULL;

        if (free_cache) {
                /*
                 * When the cache is shut down, dump it to a file if one is
                 * specified.
                 */
                isc_result_t result = dns_cache_dump(cache);
                if (result != ISC_R_SUCCESS)
                        isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE,
                                      DNS_LOGMODULE_CACHE, ISC_LOG_WARNING,
                                      "error dumping cache: %s ",
                                      isc_result_totext(result));

                /*
                 * If the cleaner task exists, let it free the cache.
                 */
                if (cache->live_tasks > 0) {
                        isc_task_shutdown(cache->cleaner.task);
                        free_cache = ISC_FALSE;
                }
        }

        UNLOCK(&cache->lock);

        if (free_cache)
                cache_free(cache);
}

void
dns_cache_attachdb(dns_cache_t *cache, dns_db_t **dbp) {
        REQUIRE(VALID_CACHE(cache));
        REQUIRE(dbp != NULL && *dbp == NULL);
        REQUIRE(cache->db != NULL);

        LOCK(&cache->lock);
        dns_db_attach(cache->db, dbp);
        UNLOCK(&cache->lock);

}

isc_result_t
dns_cache_setfilename(dns_cache_t *cache, const char *filename) {
        char *newname;

        REQUIRE(VALID_CACHE(cache));
        REQUIRE(filename != NULL);

        newname = isc_mem_strdup(cache->mctx, filename);
        if (newname == NULL)
                return (ISC_R_NOMEMORY);

        LOCK(&cache->filelock);
        if (cache->filename)
                isc_mem_free(cache->mctx, cache->filename);
        cache->filename = newname;
        UNLOCK(&cache->filelock);

        return (ISC_R_SUCCESS);
}

isc_result_t
dns_cache_load(dns_cache_t *cache) {
        isc_result_t result;

        REQUIRE(VALID_CACHE(cache));

        if (cache->filename == NULL)
                return (ISC_R_SUCCESS);

        LOCK(&cache->filelock);
        result = dns_db_load(cache->db, cache->filename);
        UNLOCK(&cache->filelock);

        return (result);
}

isc_result_t
dns_cache_dump(dns_cache_t *cache) {
        isc_result_t result;

        REQUIRE(VALID_CACHE(cache));

        if (cache->filename == NULL)
                return (ISC_R_SUCCESS);

        LOCK(&cache->filelock);
        result = dns_master_dump(cache->mctx, cache->db, NULL,
                                 &dns_master_style_cache, cache->filename);
        UNLOCK(&cache->filelock);

        return (result);
}

void
dns_cache_setcleaninginterval(dns_cache_t *cache, unsigned int t) {
        isc_interval_t interval;
        isc_result_t result;

        LOCK(&cache->lock);

        /*
         * It may be the case that the cache has already shut down.
         * If so, it has no timer.
         */
        if (cache->cleaner.cleaning_timer == NULL)
                goto unlock;

        cache->cleaner.cleaning_interval = t;

        if (t == 0) {
                result = isc_timer_reset(cache->cleaner.cleaning_timer,
                                         isc_timertype_inactive,
                                         NULL, NULL, ISC_TRUE);
        } else {
                isc_interval_set(&interval, cache->cleaner.cleaning_interval,
                                 0);
                result = isc_timer_reset(cache->cleaner.cleaning_timer,
                                         isc_timertype_ticker,
                                         NULL, &interval, ISC_FALSE);
        }
        if (result != ISC_R_SUCCESS)
                isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE,
                              DNS_LOGMODULE_CACHE, ISC_LOG_WARNING,
                              "could not set cache cleaning interval: %s",
                              isc_result_totext(result));

 unlock:
        UNLOCK(&cache->lock);
}

/*
 * Initialize the cache cleaner object at *cleaner.
 * Space for the object must be allocated by the caller.
 */

static isc_result_t
cache_cleaner_init(dns_cache_t *cache, isc_taskmgr_t *taskmgr,
                   isc_timermgr_t *timermgr, cache_cleaner_t *cleaner)
{
        isc_result_t result;
#ifdef LRU_DEBUG
        isc_interval_t interval;
#endif

        result = isc_mutex_init(&cleaner->lock);
        if (result != ISC_R_SUCCESS)
                goto fail;

        cleaner->increment = DNS_CACHE_CLEANERINCREMENT;
        cleaner->state = cleaner_s_idle;
        cleaner->cache = cache;
        cleaner->overmem = ISC_FALSE;

        cleaner->task = NULL;
        cleaner->cleaning_timer = NULL;

        if (taskmgr != NULL && timermgr != NULL) {
                result = isc_task_create(taskmgr, 1, &cleaner->task);
                if (result != ISC_R_SUCCESS) {
                        UNEXPECTED_ERROR(__FILE__, __LINE__,
                                         "isc_task_create() failed: %s",
                                         dns_result_totext(result));
                        result = ISC_R_UNEXPECTED;
                        goto cleanup;
                }
                cleaner->cache->live_tasks++;
                isc_task_setname(cleaner->task, "cachecleaner", cleaner);

                result = isc_task_onshutdown(cleaner->task,
                                             cleaner_shutdown_action, cache);
                if (result != ISC_R_SUCCESS) {
                        UNEXPECTED_ERROR(__FILE__, __LINE__,
                                         "cache cleaner: "
                                         "isc_task_onshutdown() failed: %s",
                                         dns_result_totext(result));
                        goto cleanup;
                }

                cleaner->cleaning_interval = 0; /* Initially turned off. */
                result = isc_timer_create(timermgr, isc_timertype_inactive,
                                           NULL, NULL,
                                           cleaner->task,
                                           cleaning_timer_action, cleaner,
                                           &cleaner->cleaning_timer);
                if (result != ISC_R_SUCCESS) {
                        UNEXPECTED_ERROR(__FILE__, __LINE__,
                                         "isc_timer_create() failed: %s",
                                         dns_result_totext(result));
                        result = ISC_R_UNEXPECTED;
                        goto cleanup;
                }

#ifdef LRU_DEBUG
                interval.seconds = DUMP_INTERVAL;
                interval.nanoseconds = 0;
                RUNTIME_CHECK(isc_time_nowplusinterval(&cache->dump_time,
                                                       &interval) ==
                              ISC_R_SUCCESS);
                cache->dump_timer = NULL;
                result = isc_timer_create(timermgr, isc_timertype_once,
                                          &cache->dump_time, NULL,
                                          cleaner->task, timer_dump,
                                          cache, &cache->dump_timer);
                RUNTIME_CHECK(result == ISC_R_SUCCESS); /* for brevity */
#endif
        }

        return (ISC_R_SUCCESS);

 cleanup:
        if (cleaner->cleaning_timer != NULL)
                isc_timer_detach(&cleaner->cleaning_timer);
        if (cleaner->task != NULL)
                isc_task_detach(&cleaner->task);
        DESTROYLOCK(&cleaner->lock);
 fail:
        return (result);
}

/*
 * This is run once for every cache-cleaning-interval as defined in named.conf.
 */
static void
cleaning_timer_action(isc_task_t *task, isc_event_t *event) {
        cache_cleaner_t *cleaner = event->ev_arg;

        UNUSED(task);

        INSIST(task == cleaner->task);
        INSIST(event->ev_type == ISC_TIMEREVENT_TICK);

        isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE, DNS_LOGMODULE_CACHE,
                      ISC_LOG_DEBUG(1), "cache cleaning timer fired, "
                      "cleaner state = %d", cleaner->state);

        isc_event_free(&event);
}

/*
 * Do immediate cleaning.
 */
isc_result_t
dns_cache_clean(dns_cache_t *cache, isc_stdtime_t now) {
        isc_result_t result;
        dns_dbiterator_t *iterator = NULL;

        REQUIRE(VALID_CACHE(cache));

        result = dns_db_createiterator(cache->db, ISC_FALSE, &iterator);
        if (result != ISC_R_SUCCESS)
                return result;

        result = dns_dbiterator_first(iterator);

        while (result == ISC_R_SUCCESS) {
                dns_dbnode_t *node = NULL;
                result = dns_dbiterator_current(iterator, &node,
                                                (dns_name_t *)NULL);
                if (result != ISC_R_SUCCESS)
                        break;

                /*
                 * Check TTLs, mark expired rdatasets stale.
                 */
                result = dns_db_expirenode(cache->db, node, now);
                if (result != ISC_R_SUCCESS) {
                        UNEXPECTED_ERROR(__FILE__, __LINE__,
                                         "cache cleaner: dns_db_expirenode() "
                                         "failed: %s",
                                         dns_result_totext(result));
                        /*
                         * Continue anyway.
                         */
                }

                /*
                 * This is where the actual freeing takes place.
                 */
                dns_db_detachnode(cache->db, &node);

                result = dns_dbiterator_next(iterator);
        }

        dns_dbiterator_destroy(&iterator);

        if (result == ISC_R_NOMORE)
                result = ISC_R_SUCCESS;

        return (result);
}

static void
water(void *arg, int mark) {
        dns_cache_t *cache = arg;
        isc_boolean_t overmem = ISC_TF(mark == ISC_MEM_HIWATER);

        REQUIRE(VALID_CACHE(cache));

        LOCK(&cache->cleaner.lock);

	if (overmem != cache->cleaner.overmem) {
		dns_db_overmem(cache->db, overmem);
		cache->cleaner.overmem = overmem;
		isc_mem_waterack(cache->mctx, mark);
	}

        UNLOCK(&cache->cleaner.lock);
}

void
dns_cache_setcachesize(dns_cache_t *cache, isc_uint32_t size) {
        isc_uint32_t lowater;
        isc_uint32_t hiwater;

        REQUIRE(VALID_CACHE(cache));

        /*
         * Impose a minumum cache size; pathological things happen if there
         * is too little room.
         */
        if (size != 0 && size < DNS_CACHE_MINSIZE)
                size = DNS_CACHE_MINSIZE;

        hiwater = size - (size >> 3);   /* Approximately 7/8ths. */
        lowater = size - (size >> 2);   /* Approximately 3/4ths. */

        /*
         * If the cache was overmem and cleaning, but now with the new limits
         * it is no longer in an overmem condition, then the next
         * isc_mem_put for cache memory will do the right thing and trigger
         * water().
         */

        if (size == 0 || hiwater == 0 || lowater == 0)
                /*
                 * Disable cache memory limiting.
                 */
                isc_mem_setwater(cache->mctx, water, cache, 0, 0);
        else
                /*
                 * Establish new cache memory limits (either for the first
                 * time, or replacing other limits).
                 */
                isc_mem_setwater(cache->mctx, water, cache, hiwater, lowater);
}

/*
 * The cleaner task is shutting down; do the necessary cleanup.
 */
static void
cleaner_shutdown_action(isc_task_t *task, isc_event_t *event) {
        dns_cache_t *cache = event->ev_arg;
        isc_boolean_t should_free = ISC_FALSE;

        UNUSED(task);

        INSIST(task == cache->cleaner.task);
        INSIST(event->ev_type == ISC_TASKEVENT_SHUTDOWN);

        LOCK(&cache->lock);

        cache->live_tasks--;
        INSIST(cache->live_tasks == 0);

        if (cache->references == 0)
                should_free = ISC_TRUE;

        /*
         * By detaching the timer in the context of its task,
         * we are guaranteed that there will be no further timer
         * events.
         */
        if (cache->cleaner.cleaning_timer != NULL)
                isc_timer_detach(&cache->cleaner.cleaning_timer);

#ifdef LRU_DEBUG
        isc_timer_detach(&cache->dump_timer);
#endif

        /* Make sure we don't reschedule anymore. */
        (void)isc_task_purge(task, NULL, DNS_EVENT_CACHECLEAN, NULL);

        UNLOCK(&cache->lock);

        if (should_free)
                cache_free(cache);

        isc_event_free(&event);
}

isc_result_t
dns_cache_flush(dns_cache_t *cache) {
        dns_db_t *db = NULL;
        isc_result_t result;

        result = cache_create_db(cache, &db);
        if (result != ISC_R_SUCCESS)
                return (result);

        LOCK(&cache->lock);
        LOCK(&cache->cleaner.lock);
        if (cache->cleaner.state == cleaner_s_idle) {
                /* XXXMLG do something */
        } else if (cache->cleaner.state == cleaner_s_busy) {
                /* XXXMLG do something else */
        }
        dns_db_detach(&cache->db);
        cache->db = db;
        UNLOCK(&cache->cleaner.lock);
        UNLOCK(&cache->lock);

        return (ISC_R_SUCCESS);
}

isc_result_t
dns_cache_flushname(dns_cache_t *cache, dns_name_t *name) {
        isc_result_t result;
        dns_rdatasetiter_t *iter = NULL;
        dns_dbnode_t *node = NULL;
        dns_db_t *db = NULL;

        LOCK(&cache->lock);
        if (cache->db != NULL)
                dns_db_attach(cache->db, &db);
        UNLOCK(&cache->lock);
        if (db == NULL)
                return (ISC_R_SUCCESS);
        result = dns_db_findnode(cache->db, name, ISC_FALSE, &node);
        if (result == ISC_R_NOTFOUND) {
                result = ISC_R_SUCCESS;
                goto cleanup_db;
        }
        if (result != ISC_R_SUCCESS)
                goto cleanup_db;

        result = dns_db_allrdatasets(cache->db, node, NULL,
                                     (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 = dns_db_deleterdataset(cache->db, node, NULL,
                                               rdataset.type, rdataset.covers);
                dns_rdataset_disassociate(&rdataset);
                if (result != ISC_R_SUCCESS && result != DNS_R_UNCHANGED)
                        break;
        }
        if (result == ISC_R_NOMORE)
                result = ISC_R_SUCCESS;

        dns_rdatasetiter_destroy(&iter);

 cleanup_node:
        dns_db_detachnode(cache->db, &node);

 cleanup_db:
        dns_db_detach(&db);
        return (result);
}

#ifdef LRU_DEBUG
static void
timer_dump(isc_task_t *task, isc_event_t *event) {
        dns_cache_t *cache;
        isc_interval_t interval;
        isc_time_t nexttime;

        UNUSED(task);

        cache = event->ev_arg;
        INSIST(VALID_CACHE(cache));

#ifdef LRU_DEBUG
        /* XXX: abuse existing overmem method */
        dns_db_overmem(cache->db, (isc_boolean_t)-1);
#endif

        interval.seconds = DUMP_INTERVAL;
        interval.nanoseconds = 0;

        RUNTIME_CHECK(isc_time_add(&cache->dump_time, &interval, &nexttime) ==
                      ISC_R_SUCCESS); /* XXX: this is not always true */
        cache->dump_time = nexttime;
        (void)isc_timer_reset(cache->dump_timer, isc_timertype_once,
                              &cache->dump_time, NULL, ISC_FALSE);

        isc_event_free(&event);
}
#endif