[Libguestfs] [PATCH nbdkit] nbd: Hide some state machine debugging behind a debug flag

[Eric Blake]

On Tue, May 10, 2022 at 10:43:04AM +0100, Richard W.M. Jones wrote:
> When running virt-p2v which uses this plugin, the log file is consumed
> by messages about state machine transitions and so on.  In a log file
> that was shared with me, out of the 135,023 lines in total,
> 94,653 (70%) were:
> 
>   nbdkit: debug: polling, dir=1
> 
> and 18,676 (14%) were:
> 
>   nbdkit: debug: cookie X completed state machine, status 0
> 
> This commit changes the logging so these state machine transitions are
> only printed when you use the debug flag “-D nbd.verbose=1”.  I didn't
> document this flag because it's likely only of use to developers who
> are reading the code already.
> 
> There are some debug messages along error paths which are
> (a) generally useful and (b) did not appear in the log file, so I left
> those alone.
> 
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2083498
> Reported-by: Ming Xie
> ---
>  plugins/nbd/nbd.c | 24 +++++++++++++++++-------
>  1 file changed, 17 insertions(+), 7 deletions(-)

Reviewed-by: Eric Blake <eblake at redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org