Re: [Qemu-devel] [libvirt] libvirt doesn't work with qemu 1.0

[Eric Blake <eblake@redhat.com>]

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On 12/02/2011 08:15 AM, Anthony Liguori wrote:
>> Which of course only works with new enough QEMU that is known to
>> support QMP
>> (which BTW we detect by checking the version number).
> 
> Or you could just try the -qmp option and if QEMU exits, it doesn't
> support it.  That's going to be a lot more reliable than checking a
> version number.

But we already have to call 'qemu -h' for other reasons; so we might as
well be efficient and learn as much as possible from that result than by
calling both 'qemu -h' and 'qemu -qmp ...', in order to probe what qemu
supports.

Also, 'qemu -qmp' doesn't work.  What's the proper syntax for invoking
qemu in order to query QMP capabilities, but without also starting up a
guest?

At any rate, yes, we want to improve libvirt to cache qemu capabilities,
to do the probing once at startup and then again any time the mtime of
the qemu binary changes, rather than the current policy of doing it on
every VM startup; once we cache information, making multiple probes will
still be more efficient in the long ran than the current probe per guest.

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


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