Re: [Qemu-devel] [PATCH v3 0/2] Fix migration of old pseries

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Fri, 19 Feb 2016 11:11:47 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Thu, Feb 18, 2016 at 12:32:11PM +0100, Greg Kurz wrote:
> > QEMU 2.4 broke the migration of old pseries machine with the addition
> > of configuration sections, which are sent unconditionally.
> > 
> > We assume that QEMU 2.3 is more deployed than any newer release (based on
> > the versions currently shipped by most distros). This v3 series hence
> > reverses the logic from v2: it now fully fixes migration of old pseries
> > from/to QEMU 2.3 and provides a manual workaround for the QEMU 2.4/2.4.1/2.5
> > case.
> > 
> > With this series, I could migrate the same pseries-2.3 instance in a full
> > 2.3->2.6->2.5->2.6->2.4->2.6->2.3 cycle.  
> 
> Sorry, I've lost track slightly here.  Does this series apply on top
> of, or instead of your earlier series that peeks for the config
> section?
> 

This v3 series applies instead of the v2 that peeks for the config section.

It was suggested by Laurent during review, and motivated by your decision
to favor fixing 2.3 over 2.4.

As shown in Laurent's detailed test report, migration from/to 2.3.x now works
out of the box and 2.4.x/2.5 requires qom-set.

I was also feeling a bit uncomfortable with all these machine properties to
disable the configuration section, which was explicitly coded to be non-optional
according to the changelog of commit 61964c23. The logic inversion in v3 seem
to be friendlier with the configuration section design.

Juan, could you share your thoughts ?

Thanks.

--
Greg

> > ---
> > 
> > Greg Kurz (2):
> >       spapr: skip configuration section during migration of older machines
> >       migration: allow machine to enforce configuration section migration
> > 
> > 
> >  hw/core/machine.c   |   21 +++++++++++++++++++++
> >  hw/ppc/spapr.c      |    1 +
> >  include/hw/boards.h |    1 +
> >  migration/savevm.c  |   10 ++++++++--
> >  qemu-options.hx     |    3 ++-
> >  5 files changed, 33 insertions(+), 3 deletions(-)
> >   
>