From: Alexander Duyck <alexander.h.duyck@redhat.com>
To: Jan Engelhardt <jengelh@inai.de>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>,
netfilter-devel@vger.kernel.org, kaber@trash.net,
pablo@netfilter.org
Subject: Re: [iptables PATCH] list: fix prefetch dummy
Date: Tue, 07 Apr 2015 12:29:25 -0700 [thread overview]
Message-ID: <55243015.8020402@redhat.com> (raw)
In-Reply-To: <alpine.LSU.2.20.1504072010530.17563@nerf40.vanv.qr>
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
next prev parent reply other threads:[~2015-04-07 19:29 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-06 18:05 [iptables PATCH] list: fix prefetch dummy Arturo Borrero Gonzalez
2015-04-07 0:38 ` Alexander Duyck
2015-04-07 8:37 ` Jan Engelhardt
2015-04-07 17:45 ` Alexander Duyck
2015-04-07 18:17 ` Jan Engelhardt
2015-04-07 19:29 ` Alexander Duyck [this message]
2015-04-08 17:04 ` Pablo Neira Ayuso
2015-04-09 0:18 ` Stephen Hemminger
2015-04-09 10:45 ` Pablo Neira Ayuso
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