[Qemu-devel] Querying possible -cpu variants

[Qemu-devel] Querying possible -cpu variants

[Pavel Dovgalyuk]

Hello.

 

We are making GUI for QEMU (which also should allow convenient record/replay command line
generation): https://github.com/ispras/qemu-gui

 

To fill the combo box in CPU selection form we run QEMU with "-cpu help" command and parse its
output.

The format of this list depends on target. Therefore our parsing code does not look good (and also
may corrupt someday).

 

Is there a better way of requesting this information?

 

Or we should do one of the following:

1.       Patch all targets and make the uniform "-cpu help" output format

2.       Add QMP command for requesting this list.

 

Pavel Dovgalyuk

 

Re: [Qemu-devel] Querying possible -cpu variants

[Peter Maydell]

On Fri, 25 Jan 2019 at 09:59, Pavel Dovgalyuk <dovgaluk@ispras.ru> wrote:
> To fill the combo box in CPU selection form we run QEMU with "-cpu help" command and parse its
> output.
>
> The format of this list depends on target. Therefore our parsing code does not look good (and also
> may corrupt someday).
>
> Is there a better way of requesting this information?

Yes, and you list it below...

> Or we should do one of the following:
>
> 1.       Patch all targets and make the uniform "-cpu help" output format
>
> 2.       Add QMP command for requesting this list.

...you should use QMP. The whole point of that protocol is to
be a guaranteed-not-to-break-or-change-format machine readable
way to query properties of QEMU. Don't try to hand-parse
the human-readable help output, please.

thanks
-- PMM

Re: [Qemu-devel] Querying possible -cpu variants

[Daniel P. Berrangé]

On Fri, Jan 25, 2019 at 12:58:04PM +0300, Pavel Dovgalyuk wrote:
> Hello.
> 
>  
> 
> We are making GUI for QEMU (which also should allow convenient record/replay command line
> generation): https://github.com/ispras/qemu-gui
> 
>  
> 
> To fill the combo box in CPU selection form we run QEMU with "-cpu help" command and parse its
> output.
> 
> The format of this list depends on target. Therefore our parsing code does not look good (and also
> may corrupt someday).
> 
>  
> 
> Is there a better way of requesting this information?
> 
>  
> 
> Or we should do one of the following:
> 
> 1.       Patch all targets and make the uniform "-cpu help" output format

Machine parsing of "help" output is not supported by the QEMU project.
This must all be done via the QMP interfaces.

> 2.       Add QMP command for requesting this list.

This already exists as the 'query-cpu-definitions' command


Regards,
Daniel
-- 
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Re: [Qemu-devel] Querying possible -cpu variants

[Pavel Dovgalyuk]

> From: Daniel P. Berrangé [mailto:berrange@redhat.com]
> On Fri, Jan 25, 2019 at 12:58:04PM +0300, Pavel Dovgalyuk wrote:
> >
> > We are making GUI for QEMU (which also should allow convenient record/replay command line
> > generation): https://github.com/ispras/qemu-gui
> >
> >
> >
> > To fill the combo box in CPU selection form we run QEMU with "-cpu help" command and parse
> its
> > output.
> >
> > The format of this list depends on target. Therefore our parsing code does not look good
> (and also
> > may corrupt someday).
> >


> > 2.       Add QMP command for requesting this list.
> 
> This already exists as the 'query-cpu-definitions' command

Thank you!

Pavel Dovgalyuk

Re: [Qemu-devel] Querying possible -cpu variants

[Eric Blake]

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On 1/25/19 4:10 AM, Daniel P. Berrangé wrote:

> 
>> 2.       Add QMP command for requesting this list.
> 
> This already exists as the 'query-cpu-definitions' command

What's more, you can use libvirt code as an example of how to parse QMP
commands to see what features are present.  And if the existing QMP
commands don't answer a question you need answered, enhancing QMP is a
worthwhile patch (other projects, like libvirt, will probably also end
up using those enhancements).  Among other things, we know that our
command-line parameters are not yet fully queryable by QMP.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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