Re: [Qemu-devel] Versioned machine types for ARM/non-x86 ? (Was Re: [PATCH v4 0/2] ARM: add 'virt' platform)

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

>>> However, unlike PC, I'd like to do linear versioning and avoid bumping
>>> at every release.
>>>
>>> IOW, spapr-1, spapr-2, spapr-3, etc.
>>>
>>> I think virt ought to try to do the same.
>>
>> Any particular reason why ? I kind of like the clarity of having the
>> version match the release version. Avoids needing to lookup a magic
>> decoder ring to figure out which QEMU version maps to which machine
>> version.

+1, /me likes the version-based naming too.  It's also easier to handle
on source code level as it makes it easier to reuse the #defines we
already have for pc compat properties.

> (1) reduces testing matrix by having fewer versions

I doubt that is going to fly.  It's not like we do new pc-* machine
types just for the snake of creating them, there is no policy we have to
have a new one for each release.  Usually we create them in case there
is an actual need, i.e. a incompatible change which needs a compat
property.  Which so far was the case for (almost?) every release.

> (2) makes people
> think more carefully about whether it's really necessary to break
> compatibility.

Often it's not about incompatibilities but about new features which we
wanna have enabled by default.

cheers,
  Gerd