Re: [PATCH v3 0/2] nbd/client-connection: Fix client returning a closed channel

[Eric Blake <eblake@redhat.com>]

On Thu, Nov 05, 2026 at 05:41:22PM +0100, Guillaume Vincke wrote:
> NBD client relies on lazy reconnection on error. There is a case where
> nbd_co_establish_connection() will hand back a channel disconnected by
> its peer. This leads to the request running on the dead channel. When
> reconnect-delay is set to 0 (the default), this bug prevents the
> nbd-connect thread from running on the first operation. This patch set
> addresses this specific case.
> 

> 
> v3 does not use a more robust method than sleeping to wait for the NBD
> client to reach the desired state. An option would be to add a QMP
> unstable debug query reporting the NBD client state and whether the
> connect thread has a channel ready. The test would poll this instead of
> sleeping. Would that be an acceptable follow-up?

I think an unstable query for current NBD server state (is the server
up, and if so, which exports is it serving and what is the state of
all client(s) attached to each server) would indeed make sense.  That
will probably miss this release, but I still think this series is okay
for now.  Queueing it up as a bug fix, for my upcoming pull request
intended to make it into rc0.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org