linux-kernel - Re: Strange code in include/linux/cpumask.h

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Message-Id: <200903260914.46958.rusty@rustcorp.com.au>
Date:	Thu, 26 Mar 2009 09:14:46 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Nikanth Karthikesan <knikanth@...ell.com>
Cc:	nikanth@...il.com, linux-kernel@...r.kernel.org
Subject: Re: Strange code in include/linux/cpumask.h

On Wednesday 25 March 2009 17:14:30 Nikanth Karthikesan wrote:
> On Wednesday 25 March 2009 10:41:11 Rusty Russell wrote:
> > Yes, except that this insists that bitmap be an unsigned long * or you'll
> > get a warning.  Otherwise the macro could be used on anything.  And it
> > needs to be a macro to use it as a static initializer.
> 
> Ah, got it. Thanks a lot for the explanation. May be a comment could be added 
> to the source.

Well, it's not that unusual a trick in the kernel, but an explanation might
help.

> Also looks like, this is not being used as a static initializer anywhere. 
>  i.e., Using my type-checking only version didn't trigger any error/warnings! 

It will.  cpu_all_mask uses to_cpumask, and it's replacing CPU_MASK_ALL.

> Being a deprecated interface, no new users are expected? Or is gcc smart, not 
> complaining when used as static initializer, as it would always evaluate to 
> (struct cpumask *)(bitmap)?

Yes, it seems to be.  AFAICT though, using a function in an initializer is not
valid C.

> Can the sizeof constification be removed?

Possibly, but it makes me nervous to rely on it.

Thanks,
Rusty.


> 
> Thanks
> Nikanth
> 
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