/**
  * 获取所有模块
  * @return array
  */
 public function info()
 {
     if (null == self::$_modules) {
         $rows = $this->db->select()->from('acl_module');
         $rows = $this->db->fetchAll($rows);
         self::$_modules = array();
         foreach ($rows as $row) {
             self::$_modules[$row['mod_name']] = $row['mod_desc'];
         }
     }
     return self::$_modules;
 }