Re: [PATCH] fw_cfg: Allow reboot-timeout=-1 again

[Han Han <hhan@redhat.com>]

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However, another important question is: how can we avoid such undocumented
incompatibility appears again?
I can show another case caused by such incompatibile change:
https://bugzilla.redhat.com/show_bug.cgi?id=1745868#c0

For the qemu devices, attributes, values, qmp cmds, qmp cmds arguments used
by libvirt, could we get a way to inform libvirt
that an incompatibile qemu change is coming, please update libvirt code
ASAP to adjust to that change?
Or another way that is more gently:  popping up the warning of depreciation
instead of  dropping it, and then drop it in the version
after next version.


On Tue, Oct 29, 2019 at 1:59 PM Dr. David Alan Gilbert <dgilbert@redhat.com>
wrote:

> * Markus Armbruster (armbru@redhat.com) wrote:
> > "Dr. David Alan Gilbert" <dgilbert@redhat.com> writes:
> >
> > > * Markus Armbruster (armbru@redhat.com) wrote:
> > >> "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> writes:
> > >>
> > >> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > >> >
> > >> > Commit ee5d0f89de3e53cdb0dc added range checking on reboot-timeout
> > >> > to only allow the range 0..65535; however both qemu and libvirt
> document
> > >> > the special value -1  to mean don't reboot.
> > >> > Allow it again.
> > >> >
> > >> > Fixes: ee5d0f89de3e53cdb0dc ("fw_cfg: Fix -boot reboot-timeout
> error checking")
> > >> > RH bz: https://bugzilla.redhat.com/show_bug.cgi?id=1765443
> > >> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > >> > ---
> > >> >  hw/nvram/fw_cfg.c | 5 +++--
> > >> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > >> >
> > >> > diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> > >> > index 7dc3ac378e..1a9ec44232 100644
> > >> > --- a/hw/nvram/fw_cfg.c
> > >> > +++ b/hw/nvram/fw_cfg.c
> > >> > @@ -247,10 +247,11 @@ static void fw_cfg_reboot(FWCfgState *s)
> > >> >
> > >> >      if (reboot_timeout) {
> > >> >          rt_val = qemu_opt_get_number(opts, "reboot-timeout", -1);
> > >> > +
> > >> >          /* validate the input */
> > >> > -        if (rt_val < 0 || rt_val > 0xffff) {
> > >> > +        if (rt_val < -1 || rt_val > 0xffff) {
> > >> >              error_report("reboot timeout is invalid,"
> > >> > -                         "it should be a value between 0 and
> 65535");
> > >> > +                         "it should be a value between -1 and
> 65535");
> > >> >              exit(1);
> > >> >          }
> > >> >      }
> > >>
> > >> Semantic conflict with "PATCH] qemu-options.hx: Update for
> > >> reboot-timeout parameter", Message-Id:
> > >> <20191015151451.727323-1-hhan@redhat.com>.
> > >
> > > Thanks for spotting that.
> > > I think Han and also submitted patches to review it from libvirt
> > > and it wasn't obvious what to do.  (Cc'd Han in).
> > >
> > >> I'm too tired right now to risk an opinion on which one we want.
> > >
> > > As is everyone else !  The problem here is that its documented
> > > as a valid thing to do, and libvirt does it, and you might have
> > > a current XML file that did it.  Now I think you could change libvirt
> > > to omit the reboot-timeout parameter if it was called with -1.
> > >
> > > So given its a documented thing in both qemu and libvirt xml
> > > if we want to remove it then it sohuld be deprecated properly - but
> it's
> > > already broken.
> >
> > Since commit ee5d0f89d, v4.0.0.
> >
> > If that commit had not made it into a release, we'd certainly treat the
> > loss of "-1 means don't reboot" as regression.
> >
> > But it has.  We can treat it as a regression anyway.  We can also
> > declare "ship has sailed".
> >
> > I'm leaning towads the former.
> >
> > If we restore "-1 means don't reboot", then I don't see a need to
> > deprecate it.  Just keep it.
> >
> > What do you think?
>
> That's also my view; especially since the problem seems to be an easy
> fix.
>
> Dave
>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>


-- 
Best regards,
-----------------------------------
Han Han
Quality Engineer
Redhat.

Email: hhan@redhat.com
Phone: +861065339333

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