linux-kernel - Re: generic swap()

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Message-ID: <20090206012657.GA6850@localhost>
Date:	Fri, 6 Feb 2009 09:26:57 +0800
From:	Wu Fengguang <wfg@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	L-K <linux-kernel@...r.kernel.org>
Subject: Re: generic swap()

On Fri, Jan 16, 2009 at 10:45:36AM +0100, Peter Zijlstra wrote:
> On Fri, 2009-01-16 at 01:38 -0800, Andrew Morton wrote:
> > On Fri, 16 Jan 2009 10:26:34 +0100 Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > Hi,
> > > 
> > > Where did this patch come from? -- I can't seem to find it on lkml at all..
> > 
> > That's a damn good question.  I received:
> 
> Hehe, one of the mysteries of life then :-)
> 
> > > The reason I ask it that I wonder why swap() has a return value?
> > 
> > Accident, I guess.
> > 
> > > +#define swap(a, b) ({ typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; })
> > 
> > You think it should use the do{}while(0) thing?
> 
> That was what I was thinking indeed. Non of the current users appear to
> make use of the (somewhat arbitrary) return value, so lets change it
> before someone gets creative ;-)
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

Acked-by: Wu Fengguang <fengguang.wu@...el.com>

Good change, thank you Peter.

//Sorry I was not able to read this email because of VPN issues.

Fengguang

> ---
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 343df9e..7fa3718 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -480,7 +480,8 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
>  /*
>   * swap - swap value of @a and @b
>   */
> -#define swap(a, b) ({ typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; })
> +#define swap(a, b) \
> +	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
>  
>  /**
>   * container_of - cast a member of a structure out to the containing structure
> 
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