Re: [PATCH] system: improve -mon deprecation warning

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Aug 27, 2026 at 10:56:44AM +0200, Philippe Mathieu-Daudé wrote:
> On 24/8/26 14:29, Daniel P. Berrangé wrote:
> > Expand the text a bit to make the new syntax more explicit and point
> > users to the man page for further info.
> > 
> > Reported-by: Peter Maydell <peter.maydell@linaro.org>
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >   system/vl.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/system/vl.c b/system/vl.c
> > index 061cbdf860..d5b5392569 100644
> > --- a/system/vl.c
> > +++ b/system/vl.c
> > @@ -3239,8 +3239,11 @@ void qemu_init(int argc, char **argv)
> >                   default_monitor = 0;
> >                   break;
> >               case QEMU_OPTION_mon:
> > -                warn_report_once("'-mon' is deprecated, use '-object' with "
> > -                                 "'monitor-hmp' or 'monitor-qmp' types instead");
> > +                warn_report_once("'-mon' is deprecated. Switch to either "
> > +                                 "'-object monitor-hmp,id=ID,chardev=CHR-ID' "
> > +                                 "or '-object monitor-qmp,id=qmpNN,chardev=CHR-ID' "
> > +                                 "instead. See '-object' docs in 'qemu(1)' for further "
> > +                                 "configuration guidance.");
> 
> Looking at commit 58b70f21ba6 ("docs: mark '-mon' as deprecated in
> favour of -object") I'm not sure this is a good idea to document
> '-object monitor-qmp' at all on CLI help. CLI users looking at
> help output are likely users of '-mon' for HMP. My 2 cents.

The warnings here get reported in machine use of QEMU too, not just
interactive usage. In libvirt they'll end up in
/var/log/libvirt/qemu/$GUEST.log.

I expect most end user non-managed launches of QEMU are using the
higher level -monitor for HMP, with -mon more likely machine usage.

With regards,
Daniel
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