mod_dbd.c

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    apr_status_t rv;

    rv = apr_pool_create(&rec_pool, pool);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_CRIT, rv, cfg->server,
                     "DBD: Failed to create memory pool");
        return rv;
    }

    rec = apr_pcalloc(rec_pool, sizeof(ap_dbd_t));

    rec->pool = rec_pool;

    /* The driver is loaded at config time now, so this just checks a hash.
     * If that changes, the driver DSO could be registered to unload against
     * our pool, which is probably not what we want.  Error checking isn't
     * necessary now, but in case that changes in the future ...
     */
    rv = apr_dbd_get_driver(rec->pool, cfg->name, &rec->driver);
    if (rv != APR_SUCCESS) {
        switch (rv) {
        case APR_ENOTIMPL:
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, cfg->server,
                         "DBD: driver for %s not available", cfg->name);
            break;
        case APR_EDSOOPEN:
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, cfg->server,
                         "DBD: can't find driver for %s", cfg->name);
            break;
        case APR_ESYMNOTFOUND:
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, cfg->server,
                         "DBD: driver for %s is invalid or corrupted",
                         cfg->name);
            break;
        default:
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, cfg->server,
                         "DBD: mod_dbd not compatible with APR in get_driver");
            break;
        }

        apr_pool_destroy(rec->pool);
        return rv;
    }

    rv = apr_dbd_open(rec->driver, rec->pool, cfg->params, &rec->handle);
    if (rv != APR_SUCCESS) {
        switch (rv) {
        case APR_EGENERAL:
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, cfg->server,
                         "DBD: Can't connect to %s", cfg->name);
            break;
        default:
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, cfg->server,
                         "DBD: mod_dbd not compatible with APR in open");
            break;
        }

        apr_pool_destroy(rec->pool);
        return rv;
    }

    apr_pool_cleanup_register(rec->pool, rec, dbd_close,
                              apr_pool_cleanup_null);

    /* we use a sub-pool for the prepared statements for each connection so
     * that they will be cleaned up first, before the connection is closed
     */
    rv = apr_pool_create(&prepared_pool, rec->pool);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_CRIT, rv, cfg->server,
                     "DBD: Failed to create memory pool");

        apr_pool_destroy(rec->pool);
        return rv;
    }

    rv = dbd_prepared_init(prepared_pool, cfg, rec);
    if (rv != APR_SUCCESS) {
        const char *errmsg = apr_dbd_error(rec->driver, rec->handle, rv);
        ap_log_error(APLOG_MARK, APLOG_ERR, rv, cfg->server,
                     "DBD: failed to prepare SQL statements: %s",
                     (errmsg ? errmsg : "[???]"));

        apr_pool_destroy(rec->pool);
        return rv;
    }

    *data_ptr = rec;

    return APR_SUCCESS;
}

#if APR_HAS_THREADS
static apr_status_t dbd_destroy(void *data)
{
    dbd_group_t *group = data;

    group->destroyed = 1;

    return APR_SUCCESS;
}

static apr_status_t dbd_setup(server_rec *s, dbd_group_t *group)
{
    dbd_cfg_t *cfg = group->cfg;
    apr_status_t rv;

    /* We create the reslist using a sub-pool of the pool passed to our
     * child_init hook.  No other threads can be here because we're
     * either in the child_init phase or dbd_setup_lock() acquired our mutex.
     * No other threads will use this sub-pool after this, except via
     * reslist calls, which have an internal mutex.
     *
     * We need to short-circuit the cleanup registered internally by
     * apr_reslist_create().  We do this by registering dbd_destroy()
     * as a cleanup afterwards, so that it will run before the reslist's
     * internal cleanup.
     *
     * If we didn't do this, then we could free memory twice when the pool
     * was destroyed.  When apr_pool_destroy() runs, it first destroys all
     * all the per-connection sub-pools created in dbd_construct(), and
     * then it runs the reslist's cleanup.  The cleanup calls dbd_destruct()
     * on each resource, which would then attempt to destroy the sub-pools
     * a second time.
     */
    rv = apr_reslist_create(&group->reslist,
                            cfg->nmin, cfg->nkeep, cfg->nmax,
                            apr_time_from_sec(cfg->exptime),
                            dbd_construct, dbd_destruct, group,
                            group->pool);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rv, s,
                     "DBD: failed to initialise");
        return rv;
    }

    apr_pool_cleanup_register(group->pool, group, dbd_destroy,
                              apr_pool_cleanup_null);

    return APR_SUCCESS;
}
#endif

static apr_status_t dbd_setup_init(apr_pool_t *pool, server_rec *s)
{
    dbd_group_t *group;
    apr_status_t rv = APR_SUCCESS;

    for (group = group_list; group; group = group->next) {
        apr_status_t rv2;

        rv2 = apr_pool_create(&group->pool, pool);
        if (rv2 != APR_SUCCESS) {
            ap_log_error(APLOG_MARK, APLOG_CRIT, rv2, s,
                         "DBD: Failed to create reslist cleanup memory pool");
            return rv2;
        }

#if APR_HAS_THREADS
        rv2 = dbd_setup(s, group);
        if (rv2 == APR_SUCCESS) {
            continue;
        }
        else if (rv == APR_SUCCESS) {
            rv = rv2;
        }

        /* we failed, so create a mutex so that subsequent competing callers
         * to ap_dbd_open can serialize themselves while they retry
         */
        rv2 = apr_thread_mutex_create(&group->mutex,
                                      APR_THREAD_MUTEX_DEFAULT, pool);
        if (rv2 != APR_SUCCESS) {
             ap_log_error(APLOG_MARK, APLOG_CRIT, rv2, s,
                          "DBD: Failed to create thread mutex");
             return rv2;
        }
#endif
    }

    return rv;
}

#if APR_HAS_THREADS
static apr_status_t dbd_setup_lock(server_rec *s, dbd_group_t *group)
{
    apr_status_t rv = APR_SUCCESS, rv2;

    /* several threads could be here at the same time, all trying to
     * initialize the reslist because dbd_setup_init failed to do so
     */
    if (!group->mutex) {
        /* we already logged an error when the mutex couldn't be created */
        return APR_EGENERAL;
    }

    rv2 = apr_thread_mutex_lock(group->mutex);
    if (rv2 != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rv2, s,
                     "DBD: Failed to acquire thread mutex");
        return rv2;
    }

    if (!group->reslist) {
        rv = dbd_setup(s, group);
    }

    rv2 = apr_thread_mutex_unlock(group->mutex);
    if (rv2 != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rv2, s,
                     "DBD: Failed to release thread mutex");
        if (rv == APR_SUCCESS) {
            rv = rv2;
        }
    }

    return rv;
}
#endif

/* Functions we export for modules to use:
        - open acquires a connection from the pool (opens one if necessary)
        - close releases it back in to the pool
*/
DBD_DECLARE_NONSTD(void) ap_dbd_close(server_rec *s, ap_dbd_t *rec)
{
    svr_cfg *svr = ap_get_module_config(s->module_config, &dbd_module);

    if (!svr->cfg->persist) {
        apr_pool_destroy(rec->pool);
    }
#if APR_HAS_THREADS
    else {
        apr_reslist_release(svr->group->reslist, rec);
    }
#endif
}

static apr_status_t dbd_check(apr_pool_t *pool, server_rec *s, ap_dbd_t *rec)
{
    svr_cfg *svr;
    apr_status_t rv = apr_dbd_check_conn(rec->driver, pool, rec->handle);
    const char *errmsg;

    if ((rv == APR_SUCCESS) || (rv == APR_ENOTIMPL)) {
        return APR_SUCCESS;
    }

    errmsg = apr_dbd_error(rec->driver, rec->handle, rv);
    if (!errmsg) {
        errmsg = "(unknown)";
    }

    svr = ap_get_module_config(s->module_config, &dbd_module);
    ap_log_error(APLOG_MARK, APLOG_ERR, rv, s,
                 "DBD [%s] Error: %s", svr->cfg->name, errmsg);
    return rv;
}

DBD_DECLARE_NONSTD(ap_dbd_t*) ap_dbd_open(apr_pool_t *pool, server_rec *s)
{
    svr_cfg *svr = ap_get_module_config(s->module_config, &dbd_module);
    dbd_group_t *group = svr->group;
    dbd_cfg_t *cfg = svr->cfg;
    ap_dbd_t *rec = NULL;
#if APR_HAS_THREADS
    apr_status_t rv;
#endif

    /* If nothing is configured, we shouldn't be here */
    if (cfg->name == no_dbdriver) {
        ap_log_error(APLOG_MARK, APLOG_ERR, 0, s, "DBD: not configured");
        return NULL;
    }

    if (!cfg->persist) {
        /* Return a once-only connection */
        group = apr_pcalloc(pool, sizeof(dbd_group_t));

        group->cfg = cfg;

        dbd_construct((void*) &rec, group, pool);
        return rec;
    }

#if APR_HAS_THREADS
    if (!group->reslist) {
        if (dbd_setup_lock(s, group) != APR_SUCCESS) {
            return NULL;
        }
    }

    rv = apr_reslist_acquire(group->reslist, (void*) &rec);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_ERR, rv, s,
                     "Failed to acquire DBD connection from pool!");
        return NULL;
    }

    if (dbd_check(pool, s, rec) != APR_SUCCESS) {
        apr_reslist_invalidate(group->reslist, rec);
        return NULL;
    }
#else
    /* If we have a persistent connection and it's good, we'll use it;
     * since this is non-threaded, we can update without a mutex
     */
    rec = group->rec;
    if (rec) {
        if (dbd_check(pool, s, rec) != APR_SUCCESS) {
            apr_pool_destroy(rec->pool);
            rec = NULL;
        }
    }

    /* We don't have a connection right now, so we'll open one */
    if (!rec) {
        dbd_construct((void*) &rec, group, group->pool);
        group->rec = rec;
    }
#endif

    return rec;
}

#if APR_HAS_THREADS
typedef struct {
    ap_dbd_t *rec;
    apr_reslist_t *reslist;
} dbd_acquire_t;

static apr_status_t dbd_release(void *data)
{
    dbd_acquire_t *acq = data;
    apr_reslist_release(acq->reslist, acq->rec);
    return APR_SUCCESS;
}

DBD_DECLARE_NONSTD(ap_dbd_t *) ap_dbd_acquire(request_rec *r)
{
    dbd_acquire_t *acq;

    while (!ap_is_initial_req(r)) {
        if (r->prev) {
            r = r->prev;
        }
        else if (r->main) {
            r = r->main;
        }
    }

    acq = ap_get_module_config(r->request_config, &dbd_module);
    if (!acq) {
        acq = apr_palloc(r->pool, sizeof(dbd_acquire_t));
        acq->rec = ap_dbd_open(r->pool, r->server);
        if (acq->rec) {
            svr_cfg *svr = ap_get_module_config(r->server->module_config,
                                                &dbd_module);

            ap_set_module_config(r->request_config, &dbd_module, acq);
            if (svr->cfg->persist) {
                acq->reslist = svr->group->reslist;
                apr_pool_cleanup_register(r->pool, acq, dbd_release,
                                          apr_pool_cleanup_null);
            }
        }
    }

    return acq->rec;
}

DBD_DECLARE_NONSTD(ap_dbd_t *) ap_dbd_cacquire(conn_rec *c)
{
    dbd_acquire_t *acq = ap_get_module_config(c->conn_config, &dbd_module);

    if (!acq) {
        acq = apr_palloc(c->pool, sizeof(dbd_acquire_t));
        acq->rec = ap_dbd_open(c->pool, c->base_server);
        if (acq->rec) {
            svr_cfg *svr = ap_get_module_config(c->base_server->module_config,
                                                &dbd_module);

            ap_set_module_config(c->conn_config, &dbd_module, acq);
            if (svr->cfg->persist) {
                acq->reslist = svr->group->reslist;
                apr_pool_cleanup_register(c->pool, acq, dbd_release,
                                          apr_pool_cleanup_null);
            }
        }
    }

    return acq->rec;
}
#else
DBD_DECLARE_NONSTD(ap_dbd_t *) ap_dbd_acquire(request_rec *r)
{
    ap_dbd_t *rec;

    while (!ap_is_initial_req(r)) {
        if (r->prev) {
            r = r->prev;
        }
        else if (r->main) {
            r = r->main;
        }
    }

    rec = ap_get_module_config(r->request_config, &dbd_module);
    if (!rec) {
        rec = ap_dbd_open(r->pool, r->server);
        if (rec) {
            ap_set_module_config(r->request_config, &dbd_module, rec);
        }
    }

    return rec;
}

DBD_DECLARE_NONSTD(ap_dbd_t *) ap_dbd_cacquire(conn_rec *c)
{
    ap_dbd_t *rec = ap_get_module_config(c->conn_config, &dbd_module);

    if (!rec) {
        rec = ap_dbd_open(c->pool, c->base_server);
        if (rec) {
            ap_set_module_config(c->conn_config, &dbd_module, rec);
        }
    }

    return rec;
}
#endif

static void dbd_hooks(apr_pool_t *pool)
{
    ap_hook_pre_config(dbd_pre_config, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_post_config(dbd_post_config, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_child_init((void*)dbd_setup_init, NULL, NULL, APR_HOOK_MIDDLE);

    APR_REGISTER_OPTIONAL_FN(ap_dbd_prepare);
    APR_REGISTER_OPTIONAL_FN(ap_dbd_open);
    APR_REGISTER_OPTIONAL_FN(ap_dbd_close);
    APR_REGISTER_OPTIONAL_FN(ap_dbd_acquire);
    APR_REGISTER_OPTIONAL_FN(ap_dbd_cacquire);

    apr_dbd_init(pool);
}

module AP_MODULE_DECLARE_DATA dbd_module = {
    STANDARD20_MODULE_STUFF,
    NULL,
    NULL,
    create_dbd_config,
    merge_dbd_config,
    dbd_cmds,
    dbd_hooks
};