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Editing: acache.h
/* * Copyright (C) Internet Systems Consortium, Inc. ("ISC") * * This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, you can obtain one at https://mozilla.org/MPL/2.0/. * * See the COPYRIGHT file distributed with this work for additional * information regarding copyright ownership. */ #ifndef DNS_ACACHE_H #define DNS_ACACHE_H 1 /***** ***** Module Info *****/ /* * Acache * * The Additional Cache Object * * This module manages internal caching entries that correspond to * the additional section data of a DNS DB node (an RRset header, more * accurately). An additional cache entry is expected to be (somehow) * attached to a particular RR in a particular DB node, and contains a set * of information of an additional data for the DB node. * * An additional cache object is intended to be created as a per-view * object, and manages all cache entries within the view. * * The intended usage of the additional caching is to provide a short cut * to additional glue RRs of an NS RR. For each NS RR, it is often * necessary to look for glue RRs to make a proper response. Once the * glue RRs are known, the additional caching allows the client to * associate the information to the original NS RR so that further * expensive lookups can be avoided for the NS RR. * * Each additional cache entry contains information to identify a * particular DB node and (optionally) an associated RRset. The * information consists of its zone, database, the version of the * database, database node, and RRset. * * A "negative" information can also be cached. For example, if a glue * RR does not exist as an authoritative data in the same zone as that * of the NS RR, this fact can be cached by specifying a NULL pointer * for the database, version, and node. (See the description for * dns_acache_getentry() below for more details.) * * Since each member stored in an additional cache entry holds a reference * to a corresponding object, a stale cache entry may cause unnecessary * memory consumption. For instance, when a zone is reloaded, additional * cache entries that have a reference to the zone (and its DB and/or * DB nodes) can delay the cleanup of the referred objects. In order to * minimize such a bad effect, this module provides several cleanup * mechanisms. * * The first one is a shutdown procedure called when the associated view * is shut down. In this case, dns_acache_shutdown() will be called and * all cache entries will be purged. This mechanism will help the * situation when the configuration is reloaded or the main server is * stopped. * * Per-DB cleanup mechanism is also provided. Each additional cache entry * is associated with related DB, which is expected to have been * registered when the DB was created by dns_acache_setdb(). If a * particular DB is going to be destroyed, the primary holder of the DB, * a typical example of which is a zone, will call dns_acache_putdb(). * Then this module will clean-up all cache entries associated with the * DB. This mechanism is effective when a secondary zone DB is going to * be stale after a zone transfer. * * Finally, this module supports for periodic clean-up of stale entries. * Each cache entry has a timestamp field, which is updated every time * the entry is referred. A periodically invoked cleaner checks the * timestamp of each entry, and purge entries that have not been referred * for a certain period. The cleaner interval can be specified by * dns_acache_setcleaninginterval(). If the periodic clean-up is not * enough, it is also possible to specify the upper limit of entries * in terms of the memory consumption. If the maximum value is * specified, the cleaner is invoked when the memory consumption reaches * the high watermark inferred from the maximum value. In this case, * the cleaner will use more aggressive algorithm to decide the "victim" * entries. The maximum value can be specified by * dns_acache_setcachesize(). * * When a cache entry is going to be purged within this module, the * callback function specified at the creation time will be called. * The callback function is expected to release all internal resources * related to the entry, which will typically be specific to DB * implementation, and to call dns_acache_detachentry(). The callback * mechanism is very important, since the holder of an additional cache * entry may not be able to initiate the clean-up of the entry, due to * the reference ordering. For example, as long as an additional cache * entry has a reference to a DB object, the DB cannot be freed, in which * a DB node may have a reference to the cache entry. * * Credits: * The basic idea of this kind of short-cut for frequently used * information is similar to the "pre-compiled answer" approach adopted * in nsd by NLnet LABS with RIPE NCC. Our work here is an independent * effort, but the success of nsd encouraged us to pursue this path. * * The design and implementation of the periodic memory management and * the upper limitation of memory consumption was derived from the cache * DB implementation of BIND9. * * MP: * There are two main locks in this module. One is for each entry, and * the other is for the additional cache object. * * Reliability: * The callback function for a cache entry is called with holding the * entry lock. Thus, it implicitly assumes the callback function does not * call a function that can require the lock. Typically, the only * function that can be called from the callback function safely is * dns_acache_detachentry(). The breakage of this implicit assumption * may cause a deadlock. * * Resources: * In a 32-bit architecture (such as i386), the following additional * memory is required comparing to the case that disables this module. * - 76 bytes for each additional cache entry * - if the entry has a DNS name and associated RRset, * * 44 bytes + size of the name (1-255 bytes) * * 52 bytes x number_of_RRs * - 28 bytes for each DB related to this module * * Using the additional cache also requires extra memory consumption in * the DB implementation. In the current implementation for rbtdb, we * need: * - two additional pointers for each DB node (8 bytes for a 32-bit * architecture * - for each RR associated to an RR in a DB node, we also need * a pointer and management objects to support the additional cache * function. These are allocated on-demand. The total size is * 32 bytes for a 32-bit architecture. * * Security: * Since this module does not handle any low-level data directly, * no security issue specific to this module is anticipated. * * Standards: * None. */ /*** *** Imports ***/ #include <isc/mutex.h> #include <isc/lang.h> #include <isc/stdtime.h> #include <dns/types.h> /*** *** Functions ***/ ISC_LANG_BEGINDECLS isc_result_t dns_acache_create(dns_acache_t **acachep, isc_mem_t *mctx, isc_taskmgr_t *taskmgr, isc_timermgr_t *timermgr); /* * Create a new DNS additional cache object. * * Requires: * * 'mctx' is a valid memory context * * 'taskmgr' is a valid task manager * * 'timermgr' is a valid timer or NULL. If NULL, no periodic cleaning of * the cache will take place. * * 'acachep' is a valid pointer, and *acachep == NULL * * Ensures: * * '*acachep' is attached to the newly created cache * * Returns: * * ISC_R_SUCCESS * ISC_R_NOMEMORY * ISC_R_UNEXPECTED */ void dns_acache_attach(dns_acache_t *source, dns_acache_t **targetp); /* * Attach *targetp to cache. * * Requires: * * 'acache' is a valid additional cache. * * 'targetp' points to a NULL dns_acache_t *. * * Ensures: * * *targetp is attached to the 'source' additional cache. */ void dns_acache_detach(dns_acache_t **acachep); /* * Detach *acachep from its cache. * * Requires: * * '*acachep' points to a valid additional cache. * * Ensures: * * *acachep is NULL. * * If '*acachep' is the last reference to the cache and the additional * cache does not have an outstanding task, all resources used by the * cache will be freed. */ void dns_acache_setcleaninginterval(dns_acache_t *acache, unsigned int t); /* * Set the periodic cleaning interval of an additional cache to 'interval' * seconds. */ void dns_acache_setcachesize(dns_acache_t *acache, size_t size); /* * Set the maximum additional cache size. 0 means unlimited. */ isc_result_t dns_acache_setdb(dns_acache_t *acache, dns_db_t *db); /* * Set 'db' in 'acache' when the db can be referred from acache, in order * to provide a hint for resolving the back reference. * * Requires: * 'acache' is a valid acache pointer. * 'db' is a valid DNS DB pointer. * * Ensures: * 'acache' will have a reference to 'db'. * * Returns: * ISC_R_SUCCESS * ISC_R_EXISTS (which means the specified 'db' is already set) * ISC_R_NOMEMORY */ isc_result_t dns_acache_putdb(dns_acache_t *acache, dns_db_t *db); /* * Release 'db' from 'acache' if it has been set by dns_acache_setdb(). * * Requires: * 'acache' is a valid acache pointer. * 'db' is a valid DNS DB pointer. * * Ensures: * 'acache' will release the reference to 'db'. Additionally, the content * of each cache entry that is related to the 'db' will be released via * the callback function. * * Returns: * ISC_R_SUCCESS * ISC_R_NOTFOUND (which means the specified 'db' is not set in 'acache') * ISC_R_NOMEMORY */ void dns_acache_shutdown(dns_acache_t *acache); /* * Shutdown 'acache'. * * Requires: * * '*acache' is a valid additional cache. */ isc_result_t dns_acache_createentry(dns_acache_t *acache, dns_db_t *origdb, void (*callback)(dns_acacheentry_t *, void **), void *cbarg, dns_acacheentry_t **entryp); /* * Create an additional cache entry. A new entry is created and attached to * the given additional cache object. A callback function is also associated * with the created entry, which will be called when the cache entry is purged * for some reason. * * Requires: * * 'acache' is a valid additional cache. * 'entryp' is a valid pointer, and *entryp == NULL * 'origdb' is a valid DNS DB pointer. * 'callback' and 'cbarg' can be NULL. In this case, however, the entry * is meaningless (and will be cleaned-up in the next periodical * cleaning). * * Ensures: * '*entryp' will point to a new additional cache entry. * * Returns: * ISC_R_SUCCESS * ISC_R_NOMEMORY */ isc_result_t dns_acache_getentry(dns_acacheentry_t *entry, dns_zone_t **zonep, dns_db_t **dbp, dns_dbversion_t **versionp, dns_dbnode_t **nodep, dns_name_t *fname, dns_message_t *msg, isc_stdtime_t now); /* * Get content from a particular additional cache entry. * * Requires: * * 'entry' is a valid additional cache entry. * 'zonep' is a NULL pointer or '*zonep' == NULL (this is the only * optional parameter.) * 'dbp' is a valid pointer, and '*dbp' == NULL * 'versionp' is a valid pointer, and '*versionp' == NULL * 'nodep' is a valid pointer, and '*nodep' == NULL * 'fname' is a valid DNS name. * 'msg' is a valid DNS message. * * Ensures: * Several possible cases can happen according to the content. * 1. For a positive cache entry, * '*zonep' will point to the corresponding zone (if zonep is a valid * pointer), * '*dbp' will point to a DB for the zone, * '*versionp' will point to its version, and * '*nodep' will point to the corresponding DB node. * 'fname' will have the DNS name of the DB node and contain a list of * rdataset for the node (which can be an empty list). * * 2. For a negative cache entry that means no corresponding zone exists, * '*zonep' == NULL (if zonep is a valid pointer) * '*dbp', '*versionp', and '*nodep' will be NULL. * * 3. For a negative cache entry that means no corresponding DB node * exists, '*zonep' will point to the corresponding zone (if zonep is a * valid pointer), * '*dbp' will point to a corresponding DB for zone, * '*versionp' will point to its version. * '*nodep' will be kept as NULL. * 'fname' will not change. * * On failure, no new references will be created. * * Returns: * ISC_R_SUCCESS * ISC_R_NOMEMORY */ isc_result_t dns_acache_setentry(dns_acache_t *acache, dns_acacheentry_t *entry, dns_zone_t *zone, dns_db_t *db, dns_dbversion_t *version, dns_dbnode_t *node, dns_name_t *fname); /* * Set content to a particular additional cache entry. * * Requires: * 'acache' is a valid additional cache. * 'entry' is a valid additional cache entry. * All the others pointers are NULL or a valid pointer of the * corresponding type. * * Returns: * ISC_R_SUCCESS * ISC_R_NOMEMORY * ISC_R_NOTFOUND */ bool dns_acache_cancelentry(dns_acacheentry_t *entry); /* * Cancel the use of the cache entry 'entry'. This function is supposed to * be called when the node that holds the entry finds the content is not * correct any more. This function will try to release as much dependency as * possible, and will be ready to be cleaned-up. The registered callback * function will be canceled and will never called. * * Requires: * 'entry' is a valid additional cache entry. * * Returns: * true if the entry was active when canceled */ void dns_acache_attachentry(dns_acacheentry_t *source, dns_acacheentry_t **targetp); /* * Attach *targetp to the cache entry 'source'. * * Requires: * * 'source' is a valid additional cache entry. * * 'targetp' points to a NULL dns_acacheentry_t *. * * Ensures: * * *targetp is attached to 'source'. */ void dns_acache_detachentry(dns_acacheentry_t **entryp); /* * Detach *entryp from its cache. * * Requires: * * '*entryp' points to a valid additional cache entry. * * Ensures: * * *entryp is NULL. * * If '*entryp' is the last reference to the entry, * cache does not have an outstanding task, all resources used by the * entry (including the entry object itself) will be freed. */ void dns_acache_countquerymiss(dns_acache_t *acache); /* * Count up a missed acache query. XXXMLG need more docs. */ ISC_LANG_ENDDECLS #endif /* DNS_ACACHE_H */
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