def _read_file_header(reader):
    """
    Reads SystemView trace file header.

    Parameters
    ----------
    reader : apptrace.Reader
        Trace reader object.

    Returns
    -------
    list
        a list of header lines.
    """
    empty_count = 0
    lines = []
    while empty_count < 2:
        lines.append(reader.readline(linesep='\n'))
        if lines[-1] == ';\n':
            empty_count += 1
    return lines