Greg Kurz <gk...@linux.vnet.ibm.com> wrote:
> On Fri, 19 Feb 2016 11:11:47 +1100
> David Gibson <da...@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 ?
As said previously, we don't have any better fix. We could try to make
the "enforce" thing only for some machine types, but I guess that it
would make the mess even bigger :-(
And on an unrelated topic, I guess we need to "agree" in a way to add
new features to migration for all machine types. Right now we have:
- two x86 boards
- now s390
- and now ppc
- and I guess arm is on the way
So, I guess we would need something like of what we have on
hw/i386/pc_piix.c
static void pc_compat_2_3(MachineState *machine)
{
PCMachineState *pcms = PC_MACHINE(machine);
savevm_skip_section_footers();
if (kvm_enabled()) {
pcms->smm = ON_OFF_AUTO_OFF;
}
global_state_set_optional();
savevm_skip_configuration();
}
Really, we need something like this
static void migration_compat_2_3(MachineState *machine)
{
savevm_skip_section_footers();
global_state_set_optional();
savevm_skip_configuration();
}
to be included in every machine that cares about migration. Is there
ane easy way/place where to do this globaly?
Later, Juan.
