linux-kernel - Re: Confusion in usr/include/asm-generic/fcntl.h

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Message-ID: <20090121172837.GA4386@uranus.ravnborg.org>
Date:	Wed, 21 Jan 2009 18:28:37 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Helge Deller <deller@....de>, David Miller <davem@...emloft.net>,
	jaswinder@...nel.org, mingo@...e.hu, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
	Kyle McMartin <kyle@...artin.ca>
Subject: Re: Confusion in usr/include/asm-generic/fcntl.h

On Wed, Jan 21, 2009 at 01:13:16PM +0100, Arnd Bergmann wrote:
> On Wednesday 21 January 2009, Sam Ravnborg wrote:
> > Could we add a new symbol for this?
> > We know we are going to use this in several places so a simpler variant
> > would be more readable.
> > 
> > Something like:
> > 
> > #ifdef __64BIT
> > ...
> > #endif
> > 
> > When we define __64BIT we would use the  __BITS_PER_LONG == 64 check.
> 
> I would prefer using the __BITS_PER_LONG == 64 check directly, because
> it gives you a warning when __BITS_PER_LONG is undefined, whereas the
> #ifdef check gets easily fooled by include order problems. Note that
> this is not a problem in the kernel for CONFIG_* symbols which are
> always defined before the first #include.

It gives the warning only if you add -Wundef which IIRC is not default
with -Wall. And using the "__BITS_PER_LONG == 64" the risk of gitting
the expression wrong is much higher than the simpler variant where
you only write:

    __64BIT

But I have no strong feelings for it.

	Sam
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