bind/lib/dns/cache.c

/*
 * Copyright (C) 1999-2001  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 INTERNET SOFTWARE CONSORTIUM
 * DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
 * INTERNET SOFTWARE CONSORTIUM 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 1.40 2001/06/05 22:27:51 tale Exp $ */

#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/log.h>
#include <dns/masterdump.h>
#include <dns/result.h>

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

/*
 * The following three variables control incremental cleaning.
 * MINSIZE is how many bytes is the floor for dns_cache_setcachesize().
 * CLEANERINCREMENT is how many nodes are examined in one pass.
 * CLEANERINTERVAL is the minimum amount of time between passes.
 */
#define DNS_CACHE_MINSIZE 		2097152	/* Bytes.  2097152 = 2mb */
#define DNS_CACHE_CLEANERINCREMENT	100	/* Number of nodes. */
#define DNS_CACHE_CLEANERINTERVAL	6	/* Seconds. */

/***
 ***	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 && \
			 (c)->iterator == NULL && \
			 (c)->resched_event != NULL)
#define CLEANER_BUSY(c) ((c)->state == cleaner_s_busy && \
			 (c)->iterator != NULL && \
			 (c)->resched_event == NULL)

/*
 * Accesses to a cache cleaner object are synchronized through
 * task/event serialization, or locked from the cache object.
 */
struct cache_cleaner {
	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;
	isc_event_t	*resched_event;	/* Sent by cleaner task to
					   itself to reschedule */
	isc_event_t	*overmem_event;

	dns_dbiterator_t *iterator;
	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'. */
};

/***
 ***	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
incremental_cleaning_action(isc_task_t *task, isc_event_t *event);

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

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

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) {
		UNEXPECTED_ERROR(__FILE__, __LINE__,
				 "isc_mutex_init() failed: %s",
				 dns_result_totext(result));
		result = ISC_R_UNEXPECTED;
		goto cleanup_mem;
	}

	result = isc_mutex_init(&cache->filelock);
	if (result != ISC_R_SUCCESS) {
		UNEXPECTED_ERROR(__FILE__, __LINE__,
				 "isc_mutex_init() failed: %s",
				 dns_result_totext(result));
		result = ISC_R_UNEXPECTED;
		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]);
	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);

	if (cache->cleaner.overmem_event != NULL)
		isc_event_free(&cache->cleaner.overmem_event);

	if (cache->cleaner.resched_event != NULL)
		isc_event_free(&cache->cleaner.resched_event);

	if (cache->cleaner.iterator != NULL)
		dns_dbiterator_destroy(&cache->cleaner.iterator);

	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.
		 */
		dns_cache_dump(cache);

		/*
		 * 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, 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;

	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;

	if (t < DNS_CACHE_CLEANERINTERVAL)
		t = DNS_CACHE_CLEANERINTERVAL;

	cache->cleaner.cleaning_interval = t;

	if (t == 0) {
		isc_timer_reset(cache->cleaner.cleaning_timer,
				isc_timertype_inactive, NULL, NULL, ISC_TRUE);
	} else {
		isc_interval_set(&interval, cache->cleaner.cleaning_interval,
				 0);
		isc_timer_reset(cache->cleaner.cleaning_timer,
				isc_timertype_ticker,
				NULL, &interval, ISC_FALSE);
	}
 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;

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

	cleaner->task = NULL;
	cleaner->cleaning_timer = NULL;
	cleaner->resched_event = NULL;
	cleaner->overmem_event = 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;
		}

		cleaner->resched_event =
			isc_event_allocate(cache->mctx, cleaner,
					   DNS_EVENT_CACHECLEAN,
					   incremental_cleaning_action,
					   cleaner, sizeof(isc_event_t));
		if (cleaner->resched_event == NULL) {
			result = ISC_R_NOMEMORY;
			goto cleanup;
		}
		
		cleaner->overmem_event =
			isc_event_allocate(cache->mctx, cleaner,
					   DNS_EVENT_CACHEOVERMEM,
					   overmem_cleaning_action,
					   cleaner, sizeof(isc_event_t));
		if (cleaner->overmem_event == NULL) {
			result = ISC_R_NOMEMORY;
			goto cleanup;
		}
	}

	return (ISC_R_SUCCESS);

 cleanup:
	if (cleaner->resched_event != NULL)
		isc_event_free(&cleaner->resched_event);
	if (cleaner->cleaning_timer != NULL)
		isc_timer_detach(&cleaner->cleaning_timer);
	if (cleaner->task != NULL)
		isc_task_detach(&cleaner->task);

	return (result);
}

static void
begin_cleaning(cache_cleaner_t *cleaner) {
	isc_result_t result;

	REQUIRE(CLEANER_IDLE(cleaner));

	/*
	 * Create an iterator and position it at the beginning of the cache.
	 */
	result = dns_db_createiterator(cleaner->cache->db, ISC_FALSE,
				       &cleaner->iterator);
	if (result != ISC_R_SUCCESS)
		isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE,
			      DNS_LOGMODULE_CACHE, ISC_LOG_WARNING,
			      "cache cleaner could not create "
			      "iterator: %s", isc_result_totext(result));
	else {
		dns_dbiterator_setcleanmode(cleaner->iterator, ISC_TRUE);
		result = dns_dbiterator_first(cleaner->iterator);
	}

	if (result != ISC_R_SUCCESS) {
		/*
		 * If the result is ISC_R_NOMORE, the database is empty,
		 * so there is nothing to be cleaned.
		 */
		if (result != ISC_R_NOMORE)
			UNEXPECTED_ERROR(__FILE__, __LINE__,
					 "cache cleaner: "
					 "dns_dbiterator_first() failed: %s",
					 dns_result_totext(result));

		if (cleaner->iterator != NULL)
			dns_dbiterator_destroy(&cleaner->iterator);
	} else {
		/*
		 * Pause the iterator to free its lock.
		 */
		result = dns_dbiterator_pause(cleaner->iterator);
		RUNTIME_CHECK(result == ISC_R_SUCCESS);

		isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE,
			      DNS_LOGMODULE_CACHE, ISC_LOG_DEBUG(1),
			      "begin cache cleaning, mem inuse %d",
			      isc_mem_inuse(cleaner->cache->mctx));
		cleaner->state = cleaner_s_busy;
		isc_task_send(cleaner->task, &cleaner->resched_event);
	}

	return;
}

static void
end_cleaning(cache_cleaner_t *cleaner, isc_event_t *event) {
	REQUIRE(CLEANER_BUSY(cleaner));
	REQUIRE(event != NULL);

	dns_dbiterator_destroy(&cleaner->iterator);

	dns_cache_setcleaninginterval(cleaner->cache,
				      cleaner->cleaning_interval);

	isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE, DNS_LOGMODULE_CACHE,
		      ISC_LOG_DEBUG(1), "end cache cleaning, mem inuse %d",
		      isc_mem_inuse(cleaner->cache->mctx));

	cleaner->state = cleaner_s_idle;
	cleaner->resched_event = event;
}

/*
 * 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);

	if (cleaner->state == cleaner_s_idle) {
		begin_cleaning(cleaner);

		isc_event_free(&event);
	} else
		/*
		 * incremental_cleaning_action() takes responsibility
		 * for freeing or preserving the event.
		 */
		incremental_cleaning_action(task, event);
}

/*
 * This is called when the cache either surpasses its upper limit
 * or shrinks beyond its lower limit.
 */
static void
overmem_cleaning_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 == DNS_EVENT_CACHEOVERMEM);
	INSIST(cleaner->overmem_event == NULL);

	if (cleaner->overmem) {
		if (cleaner->state == cleaner_s_idle)
			begin_cleaning(cleaner);
	} else {
		if (cleaner->state == cleaner_s_busy)
			/*
			 * end_cleaning() can't be called here because
			 * then both cleaner->overmem_event and
			 * cleaner->resched_event will point to this
			 * event.  Set the state to done, and then
			 * when the incremental_cleaning_action() event
			 * is posted, it will handle the end_cleaning.
			 */
			cleaner->state = cleaner_s_done;
	}

	cleaner->overmem_event = event;
}

/*
 * Do incremental cleaning.
 */
static void
incremental_cleaning_action(isc_task_t *task, isc_event_t *event) {
	cache_cleaner_t *cleaner = event->ev_arg;
	isc_interval_t interval;
	isc_result_t result;
	int n_names;

	UNUSED(task);

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

	if (cleaner->state == cleaner_s_done) {
		end_cleaning(cleaner, event);
		return;
	}

	INSIST(CLEANER_BUSY(cleaner));

	n_names = cleaner->increment;

	REQUIRE(DNS_DBITERATOR_VALID(cleaner->iterator));

	while (n_names-- > 0) {
		dns_dbnode_t *node = NULL;

		result = dns_dbiterator_current(cleaner->iterator, &node,
						NULL);
		if (result != ISC_R_SUCCESS) {
			UNEXPECTED_ERROR(__FILE__, __LINE__,
				 "cache cleaner: dns_dbiterator_current() "
				 "failed: %s", dns_result_totext(result));

			end_cleaning(cleaner, event);
			return;
		}

		/*
		 * The node was not needed, but was required by
		 * dns_dbiterator_current().  Give up its reference.
		 */
		dns_db_detachnode(cleaner->cache->db, &node);

		/*
		 * Step to the next node.
		 */
		result = dns_dbiterator_next(cleaner->iterator);

		if (result != ISC_R_SUCCESS) {
			/*
			 * Either the end was reached (ISC_R_NOMORE) or
			 * some error was signaled.  If the cache is still
			 * overmem and no error was encountered,
			 * keep trying to clean it, otherwise stop cleanng.
			 */
			if (result != ISC_R_NOMORE)
				UNEXPECTED_ERROR(__FILE__, __LINE__,
						 "cache cleaner: "
						 "dns_dbiterator_next() "
						 "failed: %s",
						 dns_result_totext(result));
			else if (cleaner->overmem) {
				result = dns_dbiterator_first(cleaner->
							      iterator);
				if (result == ISC_R_SUCCESS) {
					isc_log_write(dns_lctx,
						      DNS_LOGCATEGORY_DATABASE,
						      DNS_LOGMODULE_CACHE,
						      ISC_LOG_DEBUG(1),
						      "cache cleaner: "
						      "still overmem, "
						      "reset and try again");
					continue;
				}
			}

			end_cleaning(cleaner, event);
			return;
		}
	}

	/*
	 * We have successfully performed a cleaning increment but have
	 * not gone through the entire cache.  Free the iterator locks
	 * and reschedule another batch.  If it fails, just try to continue
	 * anyway.
	 */
	result = dns_dbiterator_pause(cleaner->iterator);
	RUNTIME_CHECK(result == ISC_R_SUCCESS);

	isc_log_write(dns_lctx, DNS_LOGCATEGORY_DATABASE, DNS_LOGMODULE_CACHE,
		      ISC_LOG_DEBUG(1), "cache cleaner: checked %d nodes, "
		      "mem inuse %d, sleeping",
		      cleaner->increment, isc_mem_inuse(cleaner->cache->mctx));

	/*
	 * Even though the interval timer might be in use for periodic
	 * cache cleaning, steal it for scheduling another iteration.
	 * When end_cleaning() is finally called, it will reset the
	 * interval for the periodic cleaner.
	 */
	isc_interval_set(&interval, DNS_CACHE_CLEANERINTERVAL, 0);
	isc_timer_reset(cleaner->cleaning_timer, isc_timertype_ticker,
			NULL, &interval, ISC_FALSE);

	isc_event_free(&event);

	return;
}

/*
 * 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));

	dns_db_overmem(cache->db, overmem);
	cache->cleaner.overmem = overmem;

	if (cache->cleaner.overmem_event != NULL)
		isc_task_send(cache->cleaner.task,
			      &cache->cleaner.overmem_event);
}

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);

	if (CLEANER_BUSY(&cache->cleaner))
		end_cleaning(&cache->cleaner, event);
	else
		isc_event_free(&event);

	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);

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

	UNLOCK(&cache->lock);

	if (should_free)
		cache_free(cache);
}

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);

	dns_db_detach(&cache->db);
	cache->db = db;
	return (ISC_R_SUCCESS);
}