Re: [Qemu-devel] [Qemu-stable] [PATCH 28/35] spapr: skip configuration section during migration of older machines

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Greg Kurz (2016-03-22 02:49:35)
> On Mon, 21 Mar 2016 12:28:26 -0500
> Michael Roth <mdroth@linux.vnet.ibm.com> wrote:
> 
> > From: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > 
> > Since QEMU 2.4, we have a configuration section in the migration stream.
> > This must be skipped for older machines, like it is already done for x86.
> > 
> > This patch fixes the migration of pseries-2.3 from/to QEMU 2.3, but it
> > breaks migration of the same machine from/to QEMU 2.4/2.4.1/2.5. We do
> > that anyway because QEMU 2.3 is likely to be more widely deployed than
> > newer QEMU versions.
> > 
> > Fixes: 61964c23e5ddd5a33f15699e45ce126f879e3e33
> > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > Reviewed-by: Laurent Vivier <lvivier@redhat.com>
> > Reviewed-by: Juan Quintela <quintela@redhat.com>
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > (cherry picked from commit 09b5e30da5b19f44768a5429f603caaede216757)
> > 
> > Conflicts:
> >       hw/ppc/spapr.c
> > 
> > *remove dep on 5013c5474
> > 
> > Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> > ---
> 
> This will break migration of pseries-2.3 from QEMU 2.5 to QEMU 2.5.1. Maybe
> this should be documented somewhere ?
> 
> Also, there's a companion patch to allow migration to succeed with manual
> intervention on the destination:
> 
> commit 902c053d834e3b802ec736f170edf226d4a841ff
> Author: Greg Kurz <gkurz@linux.vnet.ibm.com>
> Date:   Thu Feb 18 12:32:25 2016 +0100
> 
>     migration: allow machine to enforce configuration section migration
> 
> Maybe worth to push to stable as well ?

Yah, makes sense. I'll include this patch and document compatibility
changes in the release notes.

Is this wording correct?

"Fixes migration between QEMU 2.3 and QEMU 2.5.1 when running
pseries-2.3 machine model. Note that for migration of same
pseries-2.3 machine to/from QEMU versions 2.4.x and 2.5, 
the -machine enforce-config-section=on option now needs to be
used."

> 
> >  hw/ppc/spapr.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 6bfb908..ff1537a 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -2327,6 +2327,7 @@ static void spapr_compat_2_3(Object *obj)
> >  {
> >      savevm_skip_section_footers();
> >      global_state_set_optional();
> > +    savevm_skip_configuration();
> >  }
> > 
> >  static void spapr_compat_2_2(Object *obj)
>