Re: [Qemu-devel] [PATCH 1/2 v16] fsdev: add IO throttle support to fsdev devices

[Eric Blake]

On 02/07/2017 04:32 AM, Greg Kurz wrote:
>>
>> I'm not aware of anything related to fsdev in QMP... and libvirt seems to
>> only parse the output of -help to guess fsdev capabilities.
> 
> Oops, reading some more libvirt code I now see that libvirt doesn't parse
> -help anymore with QEMU >= 1.2.0... sorry for the noise :)
> 
>> And indeed,
>> qemu-options.hx doesn't expose this new feature.
>>
>>> Please make sure we don't reach 2.9 with only a half-baked feature;
>>> whether that means finishing the QMP work or temporarily disabling the
>>> cli additions until a later release can finish the work.
>>>   
>>
>> Would this be ok to add the missing bits in qemu-options.hx or do you
>> expect more ?

If it cannot be probed via QMP, then libvirt will most likely assume
that it does not exist.  I guess we're okay having command line only in
2.9 if you can't get QMP working, because libvirt will just never drive
the feature until 2.10 when QMP is available; but then we risk the
command line subtly changing and breaking someone else that was using
the command line without QMP.  Maybe the safest approach is to just use
the 'x-' prefix to the command line portion, until the feature is complete.

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

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