[libvirt] [PATCH] Add support for disabling S3 and S4 states

[Martin Kletzander]

On 07/30/2012 04:48 PM, Daniel P. Berrange wrote:
> On Mon, Jul 30, 2012 at 02:43:33PM +0200, Martin Kletzander wrote:
>> On 07/30/2012 02:33 PM, Daniel P. Berrange wrote:
>>> On Mon, Jul 30, 2012 at 02:25:04PM +0200, Martin Kletzander wrote:
>>>> There a two new elements in <features> implemented, which control what
>>>> ACPI sleeping states will be advertised. The default is to have both
>>>> states enabled, so this means no change for current machines.
>>>
>>>> diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
>>>> index b7562ad..859cb26 100644
>>>> --- a/docs/schemas/domaincommon.rng
>>>> +++ b/docs/schemas/domaincommon.rng
>>>> @@ -2788,6 +2788,16 @@
>>>>                <empty/>
>>>>              </element>
>>>>            </optional>
>>>> +          <optional>
>>>> +            <element name="disable_s3">
>>>> +              <empty/>
>>>> +            </element>
>>>> +          </optional>
>>>> +          <optional>
>>>> +            <element name="disable_s4">
>>>> +              <empty/>
>>>> +            </element>
>>>> +          </optional>
>>>>          </interleave>
>>>>        </element>
>>>>      </optional>
>>>
>>> This is not very nice design.  With this if an app wants to request
>>> S3, and have an error if it is not supported, they can't do that.
>>>
>>
>> I'm sorry, but I don't quite understand what do you mean. If the guest
>> wants to go to S3, there is (of course) no difference between the state
>> not being supported or the support being disabled. If an application
>> wants to request the guest to go to S3 through libvirt, then it will get
>> an appropriate message (disabled/not supported). Having one more option
>> means just setting the QEMU parameter to the default value (0).
> 
> I'm talking about the host mgmt's POV. An application creating a guest
> may want to guarantee that S3 is available to the guest. With your
> proposal, there is no way they can do that - since there is no explicit
> element in the XML to request S3. So the mgmt app may get a guest with
> S3, or it may not - it has no way of being sure. The only thing a mgmt
> app can do is forcably disable S3 .
> 

Oh, yes, I get it now. Unfortunately, that is true. Sadly, the only
thing I see we can do with QEMU is set the disable_s[34] parameter(s) to
zero, but that won't guarantee anything, I guess. Global parameters are
valid even if they don't make sense or they don't exist, so even
"qemu-kvm -global a.s=df" is a valid command-line.

Martin