linux-kernel - Re: [PATCH] bitops: simplify generic bit finding functions

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Date:	Mon, 28 Apr 2008 23:55:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] bitops: simplify generic bit finding functions

* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> So we do have cases where the inlines are obviously worth it. But in 
> general, I think we should try to move things from the header files 
> into *.c files unless there is a really clear reason for keeping it 
> that way.

there's another benefit, and in asm-x86 we prefer to move inlines to .c 
files even in borderline cases because it simplifies the type 
dependencies: not having to fully define all types at the function 
prototype site avoids include file dependency hell.

Putting things like a task struct dereference into a lowlevel inline 
file easily causes dependency problems that causes people to use macros 
instead - which have their own set of readability and side-effect 
problems.

a third argument is that inlines seldom get smaller. So if they are 
borderline and we move them into a .c, and later on the function gets 
larger, no harm is done. But if we keep the inline in a .h in the 
borderline case and we grow the inline later on, the whole kernel bloats 
in a multiplied way, without any apparent direct feedback to the 
developer that something wrong and harmful just happened.

	Ingo
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