linux-kernel - Re: [PATCH 1/1 linux-next] fs/jffs2/nodelist.h: remove unnecessary __constant

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Date:	Thu, 16 Oct 2014 09:59:04 +0200 (CEST)
From:	Fabian Frederick <fabf@...net.be>
To:	Joe Perches <joe@...ches.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mtd@...ts.infradead.org,
	David Woodhouse <dwmw2@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1 linux-next] fs/jffs2/nodelist.h: remove unnecessary
 __constant_ prefix



> On 14 October 2014 at 18:52 Joe Perches <joe@...ches.com> wrote:
>
>
> On Tue, 2014-10-14 at 18:44 +0200, Fabian Frederick wrote:
> > See commit fbdb8138cf0c
> > ("checkpatch: warn on uses of __constant_ functions")
>
> Perhaps it'd be better to use the same
> __builtin_constant_p test as swab.h and use
> just one pattern instead
>
> > diff --git a/fs/jffs2/nodelist.h b/fs/jffs2/nodelist.h
> > index fa35ff7..9f0d547 100644
> > --- a/fs/jffs2/nodelist.h
> > +++ b/fs/jffs2/nodelist.h
> > @@ -48,8 +48,8 @@
> >  #define cpu_to_je32(x) ((jint32_t){cpu_to_be32(x)})
> >  #define cpu_to_jemode(x) ((jmode_t){cpu_to_be32(os_to_jffs2_mode(x))})
> > 
> > -#define constant_cpu_to_je16(x) ((jint16_t){__constant_cpu_to_be16(x)})
> > -#define constant_cpu_to_je32(x) ((jint32_t){__constant_cpu_to_be32(x)})
> > +#define constant_cpu_to_je16(x) ((jint16_t){cpu_to_be16(x)})
> > +#define constant_cpu_to_je32(x) ((jint32_t){cpu_to_be32(x)})
>
> So none of these constant_ things would be here
> at all.

I guess you're talking about include/uapi/linux/swab.h eg       
#define __swab16(x)                             \
(__builtin_constant_p((__u16)(x)) ?     \
___constant_swab16(x) :                 \
__fswab16(x))

As your commit fbdb8138cf0c states

("Emit a warning when using any of these __constant_ forms:")

There's no need for __constant outside include/uapi.
So maybe we could just remove all #define constant_cpu_to_xxx
and always call cpu_to_xxx from jffs2 instead ?

Fabian
>
>
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