linux-kernel - Re: {PATCH] fix __packed in exported kernel headers

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Message-Id: <201106241833.15424.arnd@arndb.de>
Date:	Fri, 24 Jun 2011 18:33:15 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
Cc:	Michal Marek <mmarek@...e.cz>, Joe Perches <joe@...ches.com>,
	Nick Bowler <nbowler@...iptictech.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Frysinger <vapier@...too.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Subject: Re: {PATCH] fix __packed in exported kernel headers

On Friday 24 June 2011, Markus Trippelsdorf wrote:
> checkpatch.pl warns about using __attribute__((packed)) in kernel
> headers: "__packed is preferred over __attribute__((packed))". If one
> follows that advice it could cause problems in the exported header
> files, because the outside world doesn't know about this shortcut.
> 
> For example busybox will fail to compile:
>  CC      miscutils/ubi_attach_detach.o
>  In file included from miscutils/ubi_attach_detach.c:27:0:
>  /usr/include/mtd/ubi-user.h:330:3: error: conflicting types for ‘__packed’
>  /usr/include/mtd/ubi-user.h:314:3: note: previous declaration of ‘__packed’ was here
> ...
> 
> Fix the problem by substituting __packed with __attribute__((packed)) in
> the header_install.pl script.

No objections to the patch, but it should probably be noted that user
visible data structures should ideally not have any attributes, because
that requires building all applictions using that interface with gcc.

We generally try to add no such requirements on user applications.

	Arnd
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