Re: [Xen-devel] Re: [PATCH 1/3] xen: pvhvm: allow user to request no emulated device unplug

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

 On 08/19/2010 03:54 AM, Stefano Stabellini wrote:
> On Thu, 19 Aug 2010, Ian Campbell wrote:
>> On Thu, 2010-08-19 at 11:50 +0100, Ian Campbell wrote:
>>> On Thu, 2010-08-19 at 11:37 +0100, Stefano Stabellini wrote:
>>>> On Thu, 19 Aug 2010, Ian Campbell wrote:
>>>>>   if (r && !(r == XEN_PLATFORM_ERR_MAGIC &&
>>>>> +                 (xen_emul_unplug != -1) &&
>>>>>                   (xen_emul_unplug & XEN_UNPLUG_IGNORE)))
>>>> I wouldn't add xen_emul_unplug != -1 because it should be clear that
>>>> xen_emul_unplug & XEN_UNPLUG_IGNORE always implies xen_emul_unplug != -1.
>>> That's not correct since -1 is all 1s. So you can get a false positive
>>> for "xen_emul_unplug & XEN_UNPLUG_IGNORE" if xen_emul_unplug == -1.
>> IOW if we were to rewrite the test to use less boolean logic the patch
>> might look like:
>>
>>      if (r) {
>>              if (r != XEN_PLATFORM_ERR_MAGIC)
>>                      return;
>> +            if (xen_emul_unplug == -1)
>> +                    return;
>>              if (!(xen_emul_unplug & XEN_UNPLUG_IGNORE))
>>                      return;
>>      }
>>
>> Perhaps this refactoring is worthwhile in any case? It certainly makes
>> my head hurt less ;-)
>>
>  
> Yeah, it is probably worth it anyway :)

Treating a variable as an integer and a bitfield seems like a bad idea.

    J

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