cache_handler.c

snmp的源代码,已经在我的ubuntu下编译通过

                               int timeout, NetsnmpCacheLoad * load_hook,
                               NetsnmpCacheFree * free_hook)
{
    netsnmp_mib_handler *handler = NULL;
    handler = netsnmp_get_cache_handler(timeout, load_hook, free_hook,
                                        reginfo->rootoid,
                                        reginfo->rootoid_len);

    netsnmp_inject_handler(reginfo, handler);
    return netsnmp_register_handler(reginfo);
}

NETSNMP_STATIC_INLINE char *
_build_cache_name(const char *name)
{
    char *dup = malloc(strlen(name) + strlen(CACHE_NAME) + 2);
    if (NULL == dup)
        return NULL;
    sprintf(dup, "%s:%s", CACHE_NAME, name);
    return dup;
}

/** Insert the cache information for a given request (PDU) */
void
netsnmp_cache_reqinfo_insert(netsnmp_cache* cache,
                             netsnmp_agent_request_info * reqinfo,
                             const char *name)
{
    char *cache_name = _build_cache_name(name);
    if (NULL == netsnmp_agent_get_list_data(reqinfo, cache_name)) {
        DEBUGMSGTL(("verbose:helper:cache_handler", " adding '%s' to %p\n",
                    cache_name, reqinfo));
        netsnmp_agent_add_list_data(reqinfo,
                                    netsnmp_create_data_list(cache_name,
                                                             cache, NULL));
    }
    SNMP_FREE(cache_name);
}

/** Extract the cache information for a given request (PDU) */
netsnmp_cache  *
netsnmp_cache_reqinfo_extract(netsnmp_agent_request_info * reqinfo,
                              const char *name)
{
    netsnmp_cache  *result;
    char *cache_name = _build_cache_name(name);
    result = netsnmp_agent_get_list_data(reqinfo, cache_name);
    SNMP_FREE(cache_name);
    return result;
}

/** Extract the cache information for a given request (PDU) */
netsnmp_cache  *
netsnmp_extract_cache_info(netsnmp_agent_request_info * reqinfo)
{
    return netsnmp_cache_reqinfo_extract(reqinfo, CACHE_NAME);
}


/** Check if the cache timeout has passed. Sets and return the expired flag. */
int
netsnmp_cache_check_expired(netsnmp_cache *cache)
{
    if(NULL == cache)
        return 0;
    
    if(!cache->valid || (NULL == cache->timestamp) || (-1 == cache->timeout))
        cache->expired = 1;
    else
        cache->expired = atime_ready(cache->timestamp, 1000 * cache->timeout);
    
    return cache->expired;
}

/** Reload the cache if required */
int
netsnmp_cache_check_and_reload(netsnmp_cache * cache)
{
    if (!cache) {
        DEBUGMSG(("helper:cache_handler", " no cache\n"));
        return 0;	/* ?? or -1 */
    }
    if (!cache->valid || netsnmp_cache_check_expired(cache))
        return _cache_load( cache );
    else {
        DEBUGMSG(("helper:cache_handler", " cached (%d)\n",
                  cache->timeout));
        return 0;
    }
}

/** Is the cache valid for a given request? */
int
netsnmp_cache_is_valid(netsnmp_agent_request_info * reqinfo, 
                       const char* name)
{
    netsnmp_cache  *cache = netsnmp_cache_reqinfo_extract(reqinfo, name);
    return (cache && cache->valid);
}

/** Is the cache valid for a given request?
 * for backwards compatability. netsnmp_cache_is_valid() is preferred.
 */
int
netsnmp_is_cache_valid(netsnmp_agent_request_info * reqinfo)
{
    return netsnmp_cache_is_valid(reqinfo, CACHE_NAME);
}

/** Implements the cache handler */
int
netsnmp_cache_helper_handler(netsnmp_mib_handler * handler,
                             netsnmp_handler_registration * reginfo,
                             netsnmp_agent_request_info * reqinfo,
                             netsnmp_request_info * requests)
{
    netsnmp_cache  *cache = NULL;

    DEBUGMSGTL(("helper:cache_handler", "Got request (%d) for %s: ",
                reqinfo->mode, reginfo->handlerName));
    DEBUGMSGOID(("helper:cache_handler", reginfo->rootoid,
                 reginfo->rootoid_len));

    netsnmp_assert(handler->flags & MIB_HANDLER_AUTO_NEXT);

    cache = (netsnmp_cache *) handler->myvoid;
    if (netsnmp_ds_get_boolean(NETSNMP_DS_APPLICATION_ID,
                               NETSNMP_DS_AGENT_NO_CACHING) ||
        !cache || !cache->enabled || !cache->load_cache) {
        DEBUGMSG(("helper:cache_handler", " caching disabled or "
                  "cache not found, disabled or had no load method\n"));
        return SNMP_ERR_NOERROR;
    }

    switch (reqinfo->mode) {

    case MODE_GET:
    case MODE_GETNEXT:
    case MODE_GETBULK:
    case MODE_SET_RESERVE1: {
        netsnmp_handler_args cache_hint;

        /*
         * only touch cache once per pdu request, to prevent a cache
         * reload while a module is using cached data.
         *
         * XXX: this won't catch a request reloading the cache while
         * a previous (delegated) request is still using the cache.
         * maybe use a reference counter?
         */
        if (netsnmp_cache_is_valid(reqinfo, reginfo->handlerName))
            return SNMP_ERR_NOERROR;

        if (cache->flags & NETSNMP_CACHE_HINT_HANDLER_ARGS) {
            netsnmp_assert(NULL == cache->cache_hint);
            cache_hint.handler = handler;
            cache_hint.reginfo = reginfo;
            cache_hint.reqinfo = reqinfo;
            cache_hint.requests = requests;
            cache->cache_hint = &cache_hint;
        }

        /*
         * call the load hook, and update the cache timestamp.
         * If it's not already there, add to reqinfo
         */
        netsnmp_cache_check_and_reload(cache);
        netsnmp_cache_reqinfo_insert(cache, reqinfo, reginfo->handlerName);
        cache->cache_hint = NULL;
        /** next handler called automatically - 'AUTO_NEXT' */
        }
        return SNMP_ERR_NOERROR;

    case MODE_SET_RESERVE2:
    case MODE_SET_FREE:
    case MODE_SET_ACTION:
    case MODE_SET_UNDO:
        netsnmp_assert(netsnmp_cache_is_valid(reqinfo, reginfo->handlerName));
        /** next handler called automatically - 'AUTO_NEXT' */
        return SNMP_ERR_NOERROR;

        /*
         * A (successful) SET request wouldn't typically trigger a reload of
         *  the cache, but might well invalidate the current contents.
         * Only do this on the last pass through.
         */
    case MODE_SET_COMMIT:
        if (cache->valid && 
            ! (cache->flags & NETSNMP_CACHE_DONT_INVALIDATE_ON_SET) ) {
            cache->free_cache(cache, cache->magic);
            cache->valid = 0;
        }
        /** next handler called automatically - 'AUTO_NEXT' */
        return SNMP_ERR_NOERROR;

    default:
        snmp_log(LOG_WARNING, "cache_handler: Unrecognised mode (%d)\n",
                 reqinfo->mode);
        netsnmp_set_all_requests_error(reqinfo, requests,
                                       SNMP_ERR_GENERR);
        return SNMP_ERR_GENERR;
    }
    netsnmp_set_all_requests_error(reqinfo, requests, SNMP_ERR_GENERR);
    return SNMP_ERR_GENERR;     /* should never get here */
}

static void
_cache_free( netsnmp_cache *cache )
{
    if (NULL != cache->free_cache) {
        cache->free_cache(cache, cache->magic);
        cache->valid = 0;
    }
}

static int
_cache_load( netsnmp_cache *cache )
{
    int ret = -1;

    /*
     * If we've got a valid cache, then release it before reloading
     */
    if (cache->valid &&
        (! (cache->flags & NETSNMP_CACHE_DONT_FREE_BEFORE_LOAD)))
        _cache_free(cache);

    if ( cache->load_cache)
        ret = cache->load_cache(cache, cache->magic);
    if (ret < 0) {
        DEBUGMSG(("helper:cache_handler", " load failed (%d)\n",
                  ret));
        cache->valid = 0;
        return ret;
    }
    cache->valid = 1;
    cache->expired = 0;

    /*
     * If we didn't previously have any valid caches outstanding,
     *   then schedule a pass of the auto-release routine.
     */
    if ((!cache_outstanding_valid) &&
        (! (cache->flags & NETSNMP_CACHE_DONT_FREE_EXPIRED))) {
        snmp_alarm_register(CACHE_RELEASE_FREQUENCY,
                            0, release_cached_resources, NULL);
        cache_outstanding_valid = 1;
    }
    if (cache->timestamp)
        atime_setMarker(cache->timestamp);
    else
        cache->timestamp = atime_newMarker();
    DEBUGMSG(("helper:cache_handler", " loaded (%d)\n",
              cache->timeout));

    return ret;
}



/** run regularly to automatically release cached resources.
 * xxx - method to prevent cache from expiring while a request
 *     is being processed (e.g. delegated request). proposal:
 *     set a flag, which would be cleared when request finished
 *     (which could be acomplished by a dummy data list item in
 *     agent req info & custom free function).
 */
void
release_cached_resources(unsigned int regNo, void *clientargs)
{
    netsnmp_cache  *cache = NULL;

    cache_outstanding_valid = 0;
    DEBUGMSGTL(("helper:cache_handler", "running auto-release\n"));
    for (cache = cache_head; cache; cache = cache->next) {
        DEBUGMSGTL(("helper:cache_handler"," checking %p (flags 0x%x)\n",
                     cache, cache->flags));
        if (cache->valid &&
            ! (cache->flags & NETSNMP_CACHE_DONT_AUTO_RELEASE)) {
            DEBUGMSGTL(("helper:cache_handler","  releasing %p\n", cache));
            /*
             * Check to see if this cache has timed out.
             * If so, release the cached resources.
             * Otherwise, note that we still have at
             *   least one active cache.
             */
            if (netsnmp_cache_check_expired(cache)) {
                if(! (cache->flags & NETSNMP_CACHE_DONT_FREE_EXPIRED))
                    _cache_free(cache);
            } else {
                cache_outstanding_valid = 1;
            }
        }
    }
    /*
     * If there are any caches still valid & active,
     *   then schedule another pass.
     */
    if (cache_outstanding_valid) {
        snmp_alarm_register(CACHE_RELEASE_FREQUENCY,
                            0, release_cached_resources, NULL);
    }
}