[Libguestfs] Communication issues between NBD driver and NBDKit server

[Richard W.M. Jones]

On Sun, May 15, 2022 at 08:12:59PM +0100, Nikolaus Rath wrote:
> Do you see any way for this to happen?

I think it's impossible.  A more likely explanation follows.

If you look at the kernel code, the NBD_CMD_INFLIGHT command flag is
cleared when a command times out:

  https://github.com/torvalds/linux/blob/0cdd776ec92c0fec768c7079331804d3e52d4b27/drivers/block/nbd.c#L407

That's the place where it would have printed the "Possible stuck
request" message.

Some time later, nbdkit actually replies to the message (for the first
and only time) and in that code the flag is checked and found to be
clear already, causing the "Suspicious reply" message to be printed:

  https://github.com/torvalds/linux/blob/0cdd776ec92c0fec768c7079331804d3e52d4b27/drivers/block/nbd.c#L749

I'd say you need to increase the timeout and/or work out why the S3
plugin is taking so long to respond.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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