linux-kernel - Re: [PATCH] Use __unused0 instead of __unused for user visible struct member names

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Date:	Wed, 04 Jan 2012 12:03:16 +0100
From:	Michal Marek <mmarek@...e.cz>
To:	Guillem Jover <guillem@...rons.org>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Jonathan Nieder <jrnieder@...il.com>,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH] Use __unused0 instead of __unused for user visible struct
 member names

On 4.1.2012 09:14, Guillem Jover wrote:
> On Tue, 2012-01-03 at 07:56:59 +0100, Sam Ravnborg wrote:
>> On Mon, Jan 02, 2012 at 02:22:43PM -0600, Jonathan Nieder wrote:
>>> Guillem Jover wrote:
>>>> On BSD systems __unused has traditionally been defined to mean the
>>>> equivalent of gcc's __attribute__((__unused__)), some parts of the
>>>> Linux tree use that convention too (e.g. perf). The problem comes when
>>>> defining such macro while trying to build unmodified source code with
>>>> BSD origins on systems with Linux headers.
>>>>
>>>> Rename the user visible struct members from __unused to __unused0 to
>>>> not cause compilation failures due to that macro, which should not be
>>>> a problem as those members are supposed to be private anyway.
>>
>> ^__ is reserved for libc internal stuff and there is no reason to
>> name the unused/padding members "__unused".
>> So one or a set of patches that rename them all to something more
>> sensible would be fine.
> 
> On a quick glance, I've found other functionally similar struct
> member names present on the tree:
> 
>   __unused __unusedN __reserved __reservedN __reserved_N __resN
>   __pad __padN __flr_pad __ifi_pad __tcpm_padN __tcpct_padN
> 
> Do you mean you'd like to see patch(es) to rename all those? I'd not
> mind providing them, although my immediate concern right now is just
> regarding __unused.

__.* and _[A-Z].* are reserved for the implementation. Unfortunately,
both the kernel userspace headers and the libc are part of the
implementation, so there needs to be some common sense applied to avoid
clashes. IMO renaming __unused to __unused0 on the basis that some
headers define __unused to __attribute__((__unused__)) makes sense, but
blindly renaming any occurence of double underscore helps little.

Just my $0.02.
Michal
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