linux-kernel - Re: [PATCH 6/4] [-mm patch] use the existing offsetof().

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Date:	Thu, 20 Sep 2007 17:58:52 +0530 (IST)
From:	Satyam Sharma <satyam@...radead.org>
To:	Ken'ichi Ohmichi <oomichi@....nes.nec.co.jp>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Adrian Bunk <bunk@...nel.org>,
	kexec-ml <kexec@...ts.infradead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 6/4] [-mm patch] use the existing offsetof().



On Thu, 20 Sep 2007, Ken'ichi Ohmichi wrote:
> 
> [PATCH 6/4] [-mm patch] use the existing offsetof().
>  It is better that offsetof() is used for VMCOREINFO_OFFSET().
>  This idea is Joe Perches's.
> 
> 
> 
> Thanks
> Ken'ichi Ohmichi 
> 
> ---
> Signed-off-by: Joe Perches <joe@...ches.com>

Same deal here ...


> Signed-off-by: Ken'ichi Ohmichi <oomichi@....nes.nec.co.jp>
> ---
> diff -rpuN a/include/linux/kexec.h b/include/linux/kexec.h
> --- a/include/linux/kexec.h	2007-09-18 15:23:22.000000000 +0900
> +++ b/include/linux/kexec.h	2007-09-18 15:27:29.000000000 +0900
> @@ -137,7 +137,7 @@ unsigned long paddr_vmcoreinfo_note(void
>  			      (unsigned long)sizeof(struct name))
>  #define VMCOREINFO_OFFSET(name, field) \
>  	vmcoreinfo_append_str("OFFSET(%s.%s)=%lu\n", #name, #field, \
> -			      (unsigned long)&(((struct name *)0)->field))
> +			      (unsigned long)offsetof(struct name, field))
>  #define VMCOREINFO_LENGTH(name, value) \
>  	vmcoreinfo_append_str("LENGTH(%s)=%lu\n", #name, (unsigned long)value)

... and here. Use %zu and lose the casts.

BTW I don't think these macros are such a big win in readability or
code clarity anyway. And I noticed that there are still some open
calls to vmcoreinfo_append_str() in kexec.c (such as for the OS_RELEASE
case) which you haven't macro-ized ... we end up having code that looks
like:

	vmcoreinfo_append_str(...);
	...

	...
	VMCOREINFO_OFFSET(...);
	...

and it's not even obvious (unless you follow on to the definition of the
later macro) that the above two are *exactly* the same. So you could also
consider just losing the macros altogether.


Satyam
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