Re: [Xen-devel] [PATCH v3 2/2] xen/vm-events: Move parts of monitor_domctl code to common-side.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.02.16 at 17:28, <czuzu@xxxxxxxxxxxxxxx> wrote:
> On 2/15/2016 4:08 PM, Jan Beulich wrote:
>>
>>> After changing 1 to 1U though, I don't understand why we should also
>>> range-check mop->event.
>>> I'm imagining when (mop->event > 31):
>>> * (1U << mop->event) = 0 or >= (0x1 + 0xFFFFFFFF) (?)
>> No, it's plain undefined.
> 
> Weirdo C, didn't know that!
> I've just read http://www.danielvik.com/2010/05/c-language-quirks.html .
> That's crazy, I can't believe such 'quirks' exist and that I never knew 
> of them.
> So then, would this do:
> 
> /* sanity check - avoid '<<' operator undefined behavior */
> if ( unlikely(mop->event > 31) )
>      return -EINVAL;
> if ( unlikely(!(arch_monitor_get_capabilities(d) & (1U << mop->event))) )
>      return -EOPNOTSUPP;

I'd say -EOPNOTSUPP in both cases, but if the maintainers like
-EINVAL better I wouldn't insist on my preference.

Jan


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