Re: [Libguestfs] [libnbd PATCH] docs: Improve nbd_aio_get_direction documentation

Mention things to remember for avoiding the deadlock of polling for a POLLIN from a server that has no replies to send. Perhaps we could split the READY state into two - one for when there are no commands in flight (and get_direction returns 0 to state that polling is pointless, although a multi-threaded reader can still poll for POLLIN), and the other when there ARE commands in flight. Such a separation would also make it easier to know when nbd_aio_disconnect is not going to strand an in-flight command's response. But I'm not sure it is worth the effort. --- I'm pushing this one now, but sending the email because of the question it raises on whether we want the user to be able to distinguish a difference between any vs. no in-flight commands.