[libvirt PATCH 10/11] domain_capabilities: Add blockers attribute for CPU models

[Jiri Denemark]

On Tue, Oct 04, 2022 at 17:34:34 +0100, Daniel P. Berrangé wrote:
> On Tue, Oct 04, 2022 at 04:28:53PM +0200, Jiri Denemark wrote:
> > We already show whether a specific CPU model is usable on the current
> > host without modification via the 'usable' attribute of each CPU model.
> > But it may be useful to actually see what features are blocking each CPU
> > model from being usable. Especially when we already fetch the info from
> > QEMU and propagating it to domain capabilities XML is all we need to do.
> 
> > diff --git a/tests/domaincapsdata/qemu_4.2.0-q35.x86_64.xml b/tests/domaincapsdata/qemu_4.2.0-q35.x86_64.xml
> > index dab12e5888..8ca9e8d2b2 100644
> > --- a/tests/domaincapsdata/qemu_4.2.0-q35.x86_64.xml
> > +++ b/tests/domaincapsdata/qemu_4.2.0-q35.x86_64.xml
> > @@ -63,7 +63,7 @@
> >      <mode name='custom' supported='yes'>
> >        <model usable='yes' vendor='unknown'>qemu64</model>
> >        <model usable='yes' vendor='unknown'>qemu32</model>
> > -      <model usable='no' vendor='AMD'>phenom</model>
> > +      <model usable='no' vendor='AMD' blockers='mmxext,fxsr_opt,3dnowext,3dnow,sse4a,npt'>phenom</model>
> 
> This is an XML design anti-pattern, because it invents a data format
> inside the attribute which the caller then has to further parse.
> 
> If we want to expose this, it needs to be with child elements IMHO,
> but yes it will be more much more verbose.

You're absolutely right, but that's the only option we have I'm afraid.
Mixing subelements and text nodes is a much worse anti-pattern. I wish
the model name was in an attribute, but it isn't and having

    <model usable='no' vendor='AMD'>
      <blocker name='mmxext'/>
      phenom
    </model>

is just insane :-(

Jirka