Re: generic swap()

From: Wu Fengguang
Date: Thu Feb 05 2009 - 20:27:34 EST


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@xxxxxxxxxxxxx> 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@xxxxxxxxx>

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

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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