[Libguestfs] nbdkit does not support NBD_OPT_GO?

When trying to connect to nbdkit with imageio nbd client, I get this error: $ rm -f /tmp/nbd.sock && nbdkit file file=/var/tmp/fedora-27.img -e export -U /tmp/nbd.sock $ python -c "import logging; logging.basicConfig(level=logging.DEBUG); from ovirt_imageio_common import nbd; c = nbd.Client('/tmp/nbd.sock', 'export')" INFO:nbd:Connecting to '/tmp/nbd.sock' 'export' DEBUG:nbd:Received server flags: 3 DEBUG:nbd:Sending client flags: 1: DEBUG:nbd:Sending option: 'IHAVEOPT\x00\x00\x00\x07\x00\x00\x00\x0c' data: bytearray(b'\x00\x00\x00\x06export\x00\x00') DEBUG:nbd:Received reply [magic=3e889045565a9 option=7 type=80000001 len=0] Traceback (most recent call last): File "<string>", line 1, in <module> File "ovirt_imageio_common/nbd.py", line 126, in __init__ self._newstyle_handshake(export_name) File "ovirt_imageio_common/nbd.py", line 181, in _newstyle_handshake self._receive_go_reply() File "ovirt_imageio_common/nbd.py", line 206, in _receive_go_reply .format(ERROR_REPLY[reply], message)) ovirt_imageio_common.nbd.Error: The option sent by the client is unknown by this server implementation [message=]) According to the NBD protocol: For backwards compatibility, clients SHOULD be prepared to also handle NBD_REP_ERR_UNSUP by falling back to using NBD_OPT_EXPORT_NAME. Should I fall back to sending NBD_OPT_EXPORT_NAME, or nbkit needs to implement NBD_OPT_GO? The client code is here: https://gerrit.ovirt.org/c/93384/ Nir