private function getMetaData( ezcCacheStackMetaDataStorage $metaStorage )
    {
        $metaData = $metaStorage->restoreMetaData();
        
        if ( $metaData === null )
        {
            $metaData = call_user_func(
                array(
                    $this->properties['options']->replacementStrategy,
                    'createMetaData'
                )
            );
        }

        return $metaData;
    }