Re: [Qemu-devel] [PATCH 1/3] qapi: Report support for -device cpu hotplug in query-machines

[Eric Blake <eblake@redhat.com>]

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On 06/23/2016 08:56 PM, David Gibson wrote:
> On Thu, 23 Jun 2016 22:23:23 +0200
> Peter Krempa <pkrempa@redhat.com> wrote:
> 
>> For management apps it's very useful to know whether the selected
>> machine type supports cpu hotplug via the new -device approach. Using
>> the presence of 'query-hotpluggable-cpus' is enough for a withess.
>>

> 
> I'd been under the impression that there was a general way of detecting
> the availability of a particular qmp command.  Was I mistaken?

You are correct - query-commands says whether 'query-hotpluggable-cpus'
exists as a command.  But that is insufficient.  See my review, or the
v2 patch, where the above poor wording was corrected to say what was
really meant: knowing whether query-hotpluggable-cpus exists is
insufficient to tell you whether a given cpu type can be hotplugged.  So
adding one more piece of witness (for every type of cpu supported, we
also advertise if it is hotpluggable) is enough for libvirt to
efficiently take advantage of the new query-hotpluggable-cpus command.

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


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