def METHOD_NAME(fn):
    """
    A decorator that must be applied to functions that call if libvirt version <5.6.0.
    :param fn: function name.
    """
    def new_fn(*args, **kwargs):
        """
        Keep previous function as working before if libvirt version< 5.6.0, else do nothing
        :param args: function fixed args.
        :param kwargs: function varied args.
        """
        check_libvirt_version()
        if not IS_LIBVIRTD_SPLIT_VERSION or not LIBVIRTD_SPLIT_ENABLE_BIT:
            LOG.warn("legacy start libvirtd daemon NORMALLY with function name: %s" % fn.__name__)
            return fn(*args, **kwargs)
        else:
            LOG.warn("legacy start libvirtd daemon IGNORED with function name: %s" % fn.__name__)
            return None
    return new_fn