def init(root_helper=None):
    """Initialise oslo.privsep library.

    This function should be called at the top of main(), after the
    command line is parsed, oslo.config is initialised and logging is
    set up, but before calling any privileged entrypoint, changing
    user id, forking, or anything else "odd".

    :param root_helper: List of command and arguments to prefix
        privsep-helper with, in order to run helper as root.  Note,
        ignored if context's helper_command config option is set.
    """
    if root_helper:
        global _HELPER_COMMAND_PREFIX
        _HELPER_COMMAND_PREFIX = root_helper
