[libvirt] cpu_map data access for libxl driver

[Jiri Denemark]

On Thu, Jul 07, 2016 at 13:47:28 +0100, Daniel P. Berrange wrote:
> On Thu, Jul 07, 2016 at 02:37:39PM +0200, Cedric Bosdonnat wrote:
> > Hi Jiri, all,
> > 
> > As I mentioned earlier today on IRC, I have started implementing CPU configuration
> > support for libxl driver.
> > 
> > libxl expects a string definition the state of all the feature (easy to create), but also
> > the numeric values for the CPU family and model. virCPUDef holds the name as a string, but
> > not the numeric values though there are stored in the cpu_map.xml.

Yeah, the family/model values are currently only used for better host
CPU detection so they are not exposed outside the cpu driver.

> > For what libxl expects, search for 'cpuid=' in this man page:
> > http://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html

Oh, I was about to suggest the cpuEncode API to translate virCPUDef into
CPUID data, but now I see libxl added a new syntax which does not
require messing with raw CPUID data, which is nice.

> > Any idea how to get those values from the libxl driver?
> 
> I'd suggest just extending the virCPUDef to hold them, and populating it from
> the cpu_map.xml

This is an option, but if model/family is stored in virCPUDef, which is
just an internal representation of the <cpu> XML element, we should
probably format and parse the values. But doing so would mean users can
set them in domain XML, which I believe is not something we want to
allow. So either we will not add any formatting/parsing code for family
and model breaking the relation between *Def and XML elements, or we
need to come up with a different solution...

Another option would be to add a virCPUGetSignature API which would take
a virCPUDefPtr and return the corresponding family and model values.

Jirka