Re: [Qemu-ppc] [PATCH v2 3/3] migration: allow to suppress configuration section submission

[Greg Kurz]

On Thu, 18 Feb 2016 12:06:39 +0530
Amit Shah <address@hidden> wrote:

> On (Thu) 18 Feb 2016 [13:50:25], David Gibson wrote:
> > On Wed, Feb 17, 2016 at 05:06:43PM +0100, Greg Kurz wrote:  
> > > Since the addition of the configuration section in QEMU 2.4, it is 
> > > impossible
> > > to migrate a pseries-2.3 machine back to QEMU 2.3.
> > > 
> > > This patch makes it possible thanks to a new machine property which 
> > > allows to
> > > disable configuration section submission.
> > > 
> > > To disable submission, just add:
> > > 
> > > -machine suppress-config-section=on
> > > 
> > > Alternatively, if the target QEMU version isn't known at startup, this can
> > > be done later from the QEMU monitor with:
> > > 
> > > qom-set /machine suppress-config-section on
> > > 
> > > This property won't be automatically set for pseries-2.3 because it would
> > > then break backward migration to QEMU 2.4. If automatic behaviour is 
> > > needed,
> > > it is up to the tooling to handle this.  
> > 
> > As noted elsewhere, I'd actually be ok with enabling it for
> > pseries-2.3.  Basically we have to chose whether to work against qemu
> > 2.3 or 2.4 out of the box, we can't have both, and it sounds like qemu
> > 2.3 is more widely deployed than qemu 2.4.
> >   
> > > 
> > > Signed-off-by: Greg Kurz <address@hidden>  
> > 
> > Reviewed-by: David Gibson <address@hidden>
> > 
> > I'm not sure whose tree these need to go in via.  
> 
> I'd like to see Juan's ack, and I'm fine if you take it via your tree.
> 
> 
> 
>               Amit
> 

Hi,

I also have another option I'd like to submit. Basically, this would
be:
- introduce a enforce-config-section machine property which allows to
  override the savevm_state.skip_configuration flag
- update pseries-2.3 to skip configuration section by default (like it
  should have been done in the beginning)

It would fix migration from/to QEMU 2.3 of pseries-2.3 without manual
intervention. Only migration to/from QEMU 2.4/2.5 would require manual
use of the enforce-config-section.

Laurent, is this what you had in mind ?

--
Greg