Re: [PATCH 7/7] printk: provide a filtering macro for printk

[Mike Frysinger <vapier.adi@gmail.com>]

On Wed, Sep 2, 2009 at 08:44, Marc Andre Tanner wrote:
> On Wed, Sep 02, 2009 at 07:25:43AM -0500, Bill Gatliff wrote:
>> Jamie Lokier wrote:
>> >Looks good, except that I think kernel style is to use "do {...} while
>> >(0)" rather than "({ ... })"
>>
>> And IIRC, there was some reason for the do{...} while(0) that made
>> other alternatives not work.  So it might be more than just style at
>> issue.
>
> Do you remember the reason? I found the oposite to be ture, I actually
> started with the do { } while(0) construct but it failed in certain
> situations so I wrapped it with ({ }) and then later removed
> the now useless do { } while(0).
>
> By the way printk_once which is defined a few lines further down in
> kernel.h also uses ({ }).
>
> Anyway the next version of my patch will no longer need it.

it depends completely on how the macro is intended to be used.  if you
want to maintain the "this macro has a return value", then you have to
use ({...}).  if you want the macro to return a void, then you have to
use do{...}while(0).
-mike