case fm&fs.ModeDevice != 0:
		if fm&fs.ModeCharDevice != 0 {
			h.Typeflag = TypeChar
		} else {
			h.Typeflag = TypeBlock
		}
	case fm&fs.ModeNamedPipe != 0:
		h.Typeflag = TypeFifo
	case fm&fs.ModeSocket != 0:
		return nil, fmt.Errorf("archive/tar: sockets not supported")
	default:
		return nil, fmt.Errorf("archive/tar: unknown file mode %v", fm)
	}
	if fm&fs.ModeSetuid != 0 {
		h.Mode |= c_ISUID
	}

	}
}

type headerRoundTripTest struct {
	h  *Header
	fm fs.FileMode
}

func TestHeaderRoundTrip(t *testing.T) {
	vectors := []headerRoundTripTest{{
		// regular file.
		h: &Header{
			Name:     "test.txt",
			Mode:     0644,
			Size:     12,
			ModTime:  time.Unix(1360600916, 0),
			Typeflag: TypeReg,
		},
		fm: 0644,
	}, {
		// symbolic link.
		h: &Header{