def data_blobxfer_extra_options(conf):
    # type: (dict) -> str
    """Retrieve input data blobxfer extra options
    :param dict conf: configuration object
    :rtype: str
    :return: blobxfer extra options
    """
    try:
        eo = conf['blobxfer_extra_options']
        if eo is None:
            eo = ''
    except KeyError:
        eo = ''
    return eo