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Re: [libvirt] [PATCH] Add capabilities bit for -no-kvm-pit-reinjection



On Mon, Feb 18, 2013 at 11:13 AM, Laine Stump <laine laine org> wrote:
> On 02/18/2013 09:54 AM, Doug Goldstein wrote:
>> On Mon, Feb 18, 2013 at 7:22 AM, Laine Stump <laine laine org> wrote:
>>> On 02/18/2013 01:10 AM, Doug Goldstein wrote:
>>>> The conversion to qemuCaps dropped the ability with qemu{,-kvm} 1.2 and
>>>> newer to set the lost tick policy for the PIT. While the
>>>> -no-kvm-pit-reinjection option is depreacated, it is still supported at
>>>> least through 1.4, it is better to not lose the functionality.
>>> After 1.4 will adding it to a commandline result in an error, or will it
>>> be ignored?
>> It still exists in qemu/master.
>>
>>> Also, will something else be replacing it, or is it just no longer
>>> useful/necessary?
>> Yes. Patches coming to utilize -device
>> kvm-pit,lost-tick-policy=${valuehere} shortly. Which appeared at least
>> as early as 1.1
>>
>>> It would be a bit perturbing if an "implied" capability disappeared,
>>> with no way to detect via QMP whether or not it was there.
>> The newer command line argument cannot be detected afaik right now
>> either. But its one of those things that always exists. I plan on
>> digging into it and more patches to come. But this patch came from the
>> fact that the functionality (which unfortunately a guest needs)
>> disappeared when I switched from qemu 1.1 to 1.2. Basically this was
>> an "oh crap get the feature back" patch.
>
> Right.
>
> So the story is this:
>
> 1) in older libvirt that doesn't use qmp capabilities detection we are
> detecting presence of --no-kvm-pit-reinjection, and simply bypass it if
> it's requested but doesn't exist.
>
>
> 2) with current libvirt that uses qmp, we currently assume
> --no-kvm-pit-reinjection never exists, so silently don't add it to the
> commandline when requested.
>
> 3) with this patch, we will assume that it always exists if we have a
> qmp monitor. At least until 1.4, this is true.
>
> 4) You will be sending a patch that uses "a different method" of
> achieving the same result, and that will be in place prior to any newer
> version of qemu that may not have --no-kvm-pit-reinjection. That
> alternative has existed since at least qemu 1.1.
>
> Based on your promise of (4), ACK to this patch.
>

Thanks. Pushed. Working on the patchset for this as we speak.

-- 
Doug Goldstein


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