function listdirtree($dirname=null) {
    if(empty($dirname))exit(ibfilesystem:directoryisempty.);
    if(is_dir($dirname)) {
        if($dh=opendir($dirname)) {
            $tree=array();
            while(($file=readdir($dh))!==false) {
                if($file!=.&&$file!=..) {
                    $filepath=$dirname./.$file;
                    if(is_dir($filepath)) {
                        $tree[$file]=listdirtree($filepath);
                    } else {
                        $tree[]=$file;
                    }
                }
            }
            closedir($dh);
        } else {
            exit(ibfilesystem:cannotopendirectory$dirname.);
        }
        return$tree;
    } else {
        exit(ibfilesystem:$dirnameisnotadirectory.);
    }
}