Re: [Qemu-devel] [PATCH qom-cpu 0/9] x86: feature words array (v11) + "feature-words" property

[Andreas Färber]

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Am 02.05.2013 21:48, schrieb Eric Blake:
> On 05/02/2013 01:43 PM, Eduardo Habkost wrote:
>>> 
>>> As mentioned earlier I'd prefer to defer the property design
>>> rather than putting it lightly reviewed into 1.5 and living
>>> with some ABI. If libvirt urgently needs this info, this series
>>> needs to be reviewed and sorted out until the weekend (Hard
>>> Freeze on Monday).
>> 
>> I consider it an important bugfix for the QEMU+libvirt stack.
>> The current libvirt behavior (checking CPUID directly; not using
>> the "enforce" flag; and having its own copy of each CPU model
>> definition) is unsafe and may break live-migration silently under
>> many circumstances.
> 
> I agree that libvirt would very much like to have this in 1.5.  How
> can I help in reviewing things?

Apart from the usual QMP considerations that you will know much better
than me, I have two concerns here:
1) Polluting the QOM namespace with this dump-all implementation for
libvirt and interfering with more fine-grained property getters/setters.
2) Basing its design on current code of which we are not sure yet how
it may evolve and having to live with that for ABI stability.
Like I said, I hadn't reviewed that part yet, so couldn't pick it up
on short notice. If we get it respun and reviewed today, I can (try
to) prepare a PULL on Sunday.

On Igor's series (latest: v7 from Feb 25) I had more or less nack'ed
the attempt to introduce f-* properties due to Anthony asking for
verbose QOM property names, so we're in need of a better name, likely
something with "feature" in it, similar to what is being proposed here.
I had also argued with Anthony that QOM's object_property_add_bool()
should allow us to create a container object for accessing features in
a more simple way, such as .../icc/child[0]/cpuid-features/foo rather
than f-foo or feature-foo or foo-feature to avoid the constant
repetition and an unreadable long list of CPU properties, but the
addition of an opaque to support this was turned down.

So it boils down to the questions of where do we want to expose which
information, how should it be structured and where does/will that
information come from. Thanks.

Regards,
Andreas

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