linux-kernel - Re: [PATCH 1/4] UAPI: Fix endianness conditionals in linux/aio

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Date:	Tue, 12 Mar 2013 14:22:17 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	David Howells <dhowells@...hat.com>, torvalds@...ux-foundation.org,
	linux-arch@...r.kernel.org, sfr@...b.auug.org.au,
	Joakim.Tjernlund@...nsmode.se, arnd@...db.de, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 1/4] UAPI: Fix endianness conditionals in linux/aio_abi.h

Benjamin LaHaise <bcrl@...ck.org> writes:

> On Wed, Mar 06, 2013 at 08:47:33PM +0000, David Howells wrote:
>> In the UAPI header files, __BIG_ENDIAN and __LITTLE_ENDIAN must be compared
>> against __BYTE_ORDER in preprocessor conditionals where these are exposed to
>> userspace (that is they're not inside __KERNEL__ conditionals).
>> 
>> However, in the main kernel the norm is to check for "defined(__XXX_ENDIAN)"
>> rather than comparing against __BYTE_ORDER and this has incorrectly leaked
>> into the userspace headers.
>> 
>> The definition of PADDED() in linux/aio_abi.h is wrong in this way.  Note that
>> userspace will likely interpret this and thus the order of fields in struct
>> iocb incorrectly as the little-endian variant on big-endian machines -
>> depending on header inclusion order.
>> 
>> [!!!] NOTE [!!!]  This patch may adversely change the userspace API.  It might
>> be better to fix the ordering of aio_key and aio_reserved1 in struct iocb.
>
> It is unlikely that anyone has used the existing kernel headers and hit this 
> issue given that most existing users use the libaio.h include (which does not 
> get the endianness tests wrong).  Given that the kernel has always used the 
> correct endian mappings, this change is correct.

Agreed.

Acked-by: Jeff Moyer <jmoyer@...hat.com>
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