Re: [Xen-devel] [PATCH 1/7] Port WARN_ON_ONCE() from Linux

[Sameer Goel <sameer.goel@xxxxxxxxxx>]

On 2/13/2018 2:46 AM, Jan Beulich wrote:
>>>> On 09.02.18 at 11:47, <roger.pau@xxxxxxxxxx> wrote:
>> On Fri, Feb 09, 2018 at 10:45:25AM +0000, Julien Grall wrote:
>>> Hi,
>>>
>>> On 02/09/2018 10:29 AM, Roger Pau Monné wrote:
>>>> On Thu, Feb 08, 2018 at 08:10:49PM -0700, Sameer Goel wrote:
>>>>> diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
>>>>> index 1d9771340c..697212a061 100644
>>>>> --- a/xen/include/xen/lib.h
>>>>> +++ b/xen/include/xen/lib.h
>>>>> @@ -11,6 +11,19 @@
>>>>>   #define BUG_ON(p)  do { if (unlikely(p)) BUG();  } while (0)
>>>>>   #define WARN_ON(p) do { if (unlikely(p)) WARN(); } while (0)
>>>>> +#define WARN_ON_ONCE(p)                             \
>>>>> +({                                                  \
>>>>> +    static bool __section(".data.unlikely") __warned; \
>>>>> +    int __ret_warn_once = !!(p);                    \
>>>>         ^ bool
>>>>
>>>>> +                                                    \
>>>>> +    if ( unlikely(__ret_warn_once && !__warned) )     \
>>>>> +    {                                               \
>>>>> +        __warned = true;                            \
>>>>> +        WARN();                                     \
>>>>> +    }                                               \
>>>>> +    unlikely(__ret_warn_once);                      \
>>>> Does this macro really need to return something? It seems weird to me
>>>> to allow usages like: if ( WARN_ON_ONCE...
>>> This construct is used in Linux (included in the driver ported):
>>>
>>> if (WARN_ON_ONCE(fwspec->iommu_priv)) {
>>>      master = fwspec->iommu_priv;
>>>      smmu = master->smmu;
>>> } else {
>>> ....
>>> }
>>>
>>> IHMO the makes the code nicer to read over:
>> OK, if that's intended I'm fine with it, just wanted to check.
> But WARN_ON() should then be given the same property, I think.

Not changing any already defined macros in Xen.
>
> Jan
>
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