linux-kernel - Re: [GIT PATCH] Fix asm-avr32/dma-mapping.h breakage

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Message-ID: <Pine.LNX.4.64.0710240840390.1257@localhost.localdomain>
Date:	Wed, 24 Oct 2007 08:44:24 -0400 (EDT)
From:	"Robert P. J. Day" <rpjday@...shcourse.ca>
To:	Adrian Bunk <bunk@...nel.org>
cc:	Jens Axboe <jens.axboe@...cle.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Haavard Skinnemoen <hskinnemoen@...el.no>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PATCH] Fix asm-avr32/dma-mapping.h breakage

On Wed, 24 Oct 2007, Adrian Bunk wrote:

> On Wed, Oct 24, 2007 at 02:21:20PM +0200, Jens Axboe wrote:
> > On Wed, Oct 24 2007, Robert P. J. Day wrote:

> > > i was just about to ask -- is this one of those cases where the
> > > asm versions of scatterlist.h should have a warning/error that
> > > they should not be included directly, and to include
> > > linux/scatterlist.h instead?

> > No, using asm/scatterlist.h is perfectly fine. The problem is code
> > using the sg helpers should include linux/scatterlist.h since that
> > is where those are defined.

> > If you just need the scatterlist structure definition, then
> > asm/scatterlist.h is the correct include.

> But there's also the general question whether it's good practice for
> not architecture specific code to include asm/ headers.

> For APIs available on all architectures linux/ header are the right
> thing to use, and what is in the asm/ header and what in the linux/
> header becomes an implementation detail that can be changed.

more to the point, what the above shows is that the headers aren't
well defined.  one would think that a header file whose name is
"scatterlist.h" should provide content related solely to that name.

if there's different content, such as the "sg helpers" mentioned
above, then those should require a different header file inclusion.
it makes no sense to suggest that one should include
<asm/scatterlist.h> if you need *only* that content, but to include
<linux/scatterlist.h> if you need stuff *in addition to* the
scatterlist content.  that's just begging for confusion.

rday
-- 
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

http://crashcourse.ca
========================================================================
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