public function setReadOnly($f)
    {
        if ($f instanceof PhingFile) {
            $strPath = (string) $f->getPath();
            $perms = (int) (@fileperms($strPath) & 0444);

            FileSystem::getFileSystem()->chmod($strPath, $perms);
        } else {
            throw new Exception("IllegalArgumentType: Argument is not File");
        }
    }