Re: [Qemu-devel] [libvirt] [PATCH qom-cpu 6/9] target-i386: Add "feature-words" property

[Eric Blake <eblake@redhat.com>]

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On 04/22/2013 01:00 PM, Eduardo Habkost wrote:
> This property will be useful for libvirt, as libvirt already has logic
> based on low-level feature bits (not feature names), so it will be
> really easy to convert the current libvirt logic to something using the
> "feature-words" property.
> 
> The property will have two main use cases:
>  - Checking host capabilities, by checking the features of the "host"
>    CPU model
>  - Checking which features are enabled on each CPU model
> 
> Example output:
> 
>   $ ./QMP/qmp --path=/tmp/m qom-get --path=/machine/unattached/device[1] --property=feature-words

If I'm not mistaken, the QMP counterpart that libvirt will use is:

{ "execute":"qom-get",
  "arguments": { "path":"/machine/unattached/device[1]",
                 "property":"feature-words" } }

>   item[0].cpuid-register: EDX
>   item[0].cpuid-input-eax: 2147483658
>   item[0].features: 0
>   item[1].cpuid-register: EAX
>   item[1].cpuid-input-eax: 1073741825
>   item[1].features: 0
>   item[2].cpuid-register: EDX
>   item[2].cpuid-input-eax: 3221225473
>   item[2].features: 0
>   item[3].cpuid-register: ECX
>   item[3].cpuid-input-eax: 2147483649
>   item[3].features: 101
>   item[4].cpuid-register: EDX
>   item[4].cpuid-input-eax: 2147483649
>   item[4].features: 563346425
>   item[5].cpuid-register: EBX
>   item[5].cpuid-input-eax: 7
>   item[5].features: 0
>   item[5].cpuid-input-ecx: 0
>   item[6].cpuid-register: ECX
>   item[6].cpuid-input-eax: 1
>   item[6].features: 2155880449
>   item[7].cpuid-register: EDX
>   item[7].cpuid-input-eax: 1
>   item[7].features: 126614521

And this would then be returned as a JSON array containing struct
members looking like this:

> +{ 'type': 'X86CPUFeatureWordInfo',
> +  'data': { 'cpuid-input-eax': 'int',
> +            '*cpuid-input-ecx': 'int',
> +            'cpuid-register': 'X86CPURegister32',
> +            'features': 'int' } }

Looks reasonable (and better than what we've had in the past!), although
I'll let Jiri Denemark give final say on whether it meets libvirt's needs.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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