def get_subfunctions(filename):
    """
    Retrieves the subfunctions from a platform.conf file.
    :param filename: file to retrieve subfunctions from
    :return: a list of the subfunctions or None if no subfunctions exist
    """
    matchstr = 'subfunction='

    with open(filename, 'r') as f:
        for line in f:
            if matchstr in line:
                parsed = line.split('=')
                return parsed[1].rstrip().split(",")
    return