Re: [Qemu-devel] [PATCH] monitor: introduce query-config-schema

[Paolo Bonzini <pbonzini@redhat.com>]

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Il 22/04/2013 17:00, Eric Blake ha scritto:
> On 04/22/2013 06:07 AM, Paolo Bonzini wrote:
>> Il 22/04/2013 13:48, Amos Kong ha scritto:
>>>>>>> Libvirt doesn't have a stable way to know option
>>>>>>> support detail. This patch introdued a new qmp command
>>>>>>> to query configuration schema information. hmp command
>>>>>>> isn't added.
>>>>> 
>>>>> Can you introspect QemuOpts instead?  All new options are
>>>>> added there.
>>> 
>>> It would be exact to use QemuOpts. I tried to output the
>>> vm_config_groups[] in qemu-config.c, but it seems not enough.
>>> (desc list of -netdev, -drive, -device are all empty)
>> 
>> That's expected because they are parsed otherwise, depending on
>> the backend type.  -chardev is currently working but it's an
>> implementation detail.
> 
> Libvirt cares most about newly added options, which should use
> qemuOpts all the way.  We can understand that legacy options like
> -netdev might not yet use qemuOpts, but they are also legacy
> options, and therefore libvirt can already assume they exist since
> at least qemu 1.3 (when libvirt switched over to QMP probing).  If
> we later add a new feature to -netdev, we should also convert
> -netdev to qemuOpts at that time, so that libvirt would know
> whether the new feature is available.

- -netdev is not a legacy option.  -netdev/-drive/-device do use
QemuOpts, but not for validation.  They create an object, and let the
object parse the option.

They are more complex than the other option, and need a different kind
of introspection (on the properties of a class, or something like that).

Paolo

> At any rate, we really DO want introspection, and having it in 1.5
> is a worthwhile goal.  Even if the introspection turns up empty on
> legacy options, having it for the sake of new options is worth the
> effort.
> 

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