Re: [libvirt] [PATCH 3/3] qemu: Adapt to changed ppc64 CPU model names
On Tue, May 22, 2018 at 11:02:17 +0200, Andrea Bolognani wrote:
On Thu, 2018-05-17 at 17:33 +0200, Jiri Denemark wrote:
[...]
> --- a/tests/domaincapsschemadata/qemu_2.12.0.ppc64.xml
> +++ b/tests/domaincapsschemadata/qemu_2.12.0.ppc64.xml
> @@ -25,7 +25,11 @@
> <mode name='host-model' supported='yes'>
> <model fallback='allow'>POWER8</model>
> </mode>
This is quite suspicious - it looks like a proper CPU model, but
it's really a compatibility mode, so it should be lowercase rather
than uppercase. You certainly won't be able to use
<cpu mode='host-model>
<model>POWER8</model>
</cpu>
so why are we advertising the uppercase variant here? Am I missing
something?
Hmm, you're right. In general, this is advertising the host CPU (ideally
as seen by QEMU), which doesn't really work for ppc since host-model was
misused for compatibility modes. I think we'll have to add a special
hack to produce <mode name='host-model' supported='yes'/> without
showing any CPU model. Ideally, we would somehow list all supported
compatibility modes, but this can be left for the future.
> - <mode name='custom' supported='no'/>
> + <mode name='custom' supported='yes'>
> + <model usable='unknown'>POWER9</model>
> + <model usable='unknown'>POWER8</model>
> + <model usable='unknown'>POWER7</model>
> + </mode>
This is of course an improvement, but I'm not sure we want to keep
exposing uppercase model names to users.
I understand we need to keep accepting them for compatibility
reasons, but since QEMU has moved to lowercase CPU model names
wouldn't it make sense for libvirt to follow suit?
I don't think so. Introducing new aliases (i.e., lower case variants)
for the existing models would IMHO cause more troubles than having a
mixture of upper case and lower case names (once something like power10
is introduced). Users or apps would have to use a crystal ball to check
which CPU model name would be compatible with older libvirt.
Jirka