Re: [RFC PATCH 1/1] qtest/migration: Support more than one QEMU binary

[Thomas Huth <thuth@redhat.com>]

On 04/10/2023 20.09, Juan Quintela wrote:
> Daniel P. Berrangé <berrange@redhat.com> wrote:
>> On Wed, Oct 04, 2023 at 12:59:49PM -0300, Fabiano Rosas wrote:
>>> Juan Quintela <quintela@redhat.com> writes:
>>>
>>>> Fabiano Rosas <farosas@suse.de> wrote:
>>>>> Daniel P. Berrangé <berrange@redhat.com> writes:
>>>>>
>>>>>> On Tue, Oct 03, 2023 at 05:24:50PM +0200, Philippe Mathieu-Daudé wrote:
>>>> [...]
> 
>>> I'm working on a cleanup of this patch to make it more integrated with
>>> libqtest. If we teach qtest_get_machines() to sometimes refresh the list
>>> of machines then it becomes way less code.
>>>
>>>> I think that it is just easier to pass the machine type we want to test
>>>> to whatever script we have.  Specially where [sane] architectures like
>>>> arm don't have a default machine type (no, I haven't double checked if
>>>> that has changed lately).
>>>
>>> We still need to enforce the same machine type for both binaries and a
>>> sane range of QEMU versions. I think our docs state that we only support
>>> migration from QEMU n->n+1 and vice versa? If the test will know what
>>> combinations are allowed, it could just go ahead and use those.
>>
>> Query the 'pc' (or 'q35' as appropriate) alias on both QEMU versions,
>> to resolve them into versioned machines.
>>
>> Then find which resolved machine version(s) exist in both QEMUs, and
>> prefer the src machine if multiple matches exist.
> 
> We only change Machine Type with each qemu version, so having to change
> it by hand don't look so complicated.
> 
> Let's assume for a moment that "pc" and "q35" machine types don't exist
> (rest of architectures needs to do a similar thing)
> 
> latest qemu has:
> pc-i440fx-8.2        Standard PC (i440FX + PIIX, 1996) (default)
> pc-i440fx-8.1        Standard PC (i440FX + PIIX, 1996) (default)
> pc-i440fx-8.0        Standard PC (i440FX + PIIX, 1996) (default)
> pc-i440fx-7.2        Standard PC (i440FX + PIIX, 1996) (default)
> 
> Previous version one has everything except 8.2
> 
> We want to test:
> 
> (this is what we do now)
> qemu-8.2 -M pc-i440fx-8.2  -> qemu-8.2 -M pc-i440fx-8.2
> 
> And we want to test additionally:
> 
> qemu-8.1 -M pc-i440fx-8.1  -> qemu-8.2 -M pc-i440fx-8.1
> qemu-8.2 -M pc-i440fx-8.1  -> qemu-8.1 -M pc-i440fx-8.1
> 
> And that is it.
> 
> So the thing that we need is a sane way to get qtest_init() to use the
> right machine type without inventing what machine type they want.  Not
> having a default machine type has other advantages, but that is a
> different discussion.

Not sure whether it's useful for you, but have a look at 
qtest_cb_for_every_machine() and qtest_is_old_versioned_machine() ... there 
is already some logic in there to find out the latest machine version, maybe 
you can re-use some of the code in there.

  Thomas