Re: [iptables PATCH] list: fix prefetch dummy

[Alexander Duyck <alexander.h.duyck@redhat.com>]

On 04/07/2015 11:17 AM, Jan Engelhardt wrote:
>
> On Tuesday 2015-04-07 19:45, Alexander Duyck wrote:
>>>>>   -#define prefetch(x)		1
>>>>> +#define prefetch(x)		((void)0)
>>>>>
>>>> Why not just use "do {} while (0)"?  I know that is what is used in the
>>>> kernel for functions that don't do anything.
>>> I may be getting the terms wrong, but:
>>> do{}while(0) is not an expression, it is a (block) control statement.
>>> In particular, do{}while(0) won't evaluate to an rvalue.
>>
>> Right.  That is the point in this case.  I am assuming what Arturo is trying to
>> accomplish since you shouldn't be able to evaluate ((void)0) as an rvalue
>> either.
>
> The difference is that
>
> 	int i;
> 	i = 1, (void)0;
>
> compiles, while
>
> 	i = 1, do{}while(0);
>

Okay, that explains it.  It is being used inside the init, condition, 
and post process sections of a for loop.  Thanks for explaining it.

- Alex