Re: generic swap()

[Wu Fengguang <wfg@linux.intel.com>]

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@infradead.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@chello.nl>

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