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Re: [libvirt] [PATCH 09/14] Fix check for whether a suspend target is supported



On 11/29/2011 10:10 PM, Daniel P. Berrange wrote:

> On Tue, Nov 29, 2011 at 09:33:09AM -0700, Eric Blake wrote:
>> On 11/29/2011 08:44 AM, Daniel P. Berrange wrote:
>>> From: "Daniel P. Berrange" <berrange redhat com>
>>>
>>> hostPMFeatures is a bitmask, but the VIR_NODE_SUSPEND_TARGET
>>> constants are from an enum. Thus the code was checking the
>>> wrong bit values
>>
>> Yep - regression introduced in patch 1/14.  Maybe you should squash this
>> in to that patch, so that bisecting doesn't hit the regression (although
>> that would mean patching a different file, since you moved the function
>> location in the meantime).  Up to you if you want to go to the hassle.
> 
> It wasn't a regression actually. This code was still using the
> duplicate enum at that point:
> 
>   enum virHostPMCapability {
>      VIR_HOST_PM_S3,              /* Suspend-to-RAM */
>      VIR_HOST_PM_S4,              /* Suspend-to-Disk */
>      VIR_HOST_PM_HYBRID_SUSPEND,  /* Hybrid-Suspend */
> 
>      VIR_HOST_PM_LAST
>  };
> 
> So AFAICT, it was broken from the start.
> 


I beg to differ here. It was a bit weird, but definitely not broken.
Since VIR_HOST_PM_S3 etc were linear (0,1,2), a bit-wise OR operation
was carried out like this: *bitmask |= 1U << feature; where feature
was one of the above.

And while checking this, we used to do:
hostPMFeatures & VIR_NODE_SUSPEND_TARGET_HYBRID

where VIR_NODE_SUSPEND_TARGET_HYBRID etc were like 1 << 0, 1 << 1 etc

Thus, this was ugly, but not broken. Otherwise, it would have surely
failed my suspend tests which I ran every time before submitting the
patches :-)

-- 
Regards,
Srivatsa S. Bhat
IBM Linux Technology Center


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