linux-kernel - Re: [PATCH] kobject: Suppress compiler warning with gcc 3.x

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Message-ID: <m1k4qgr54j.fsf@fess.ebiederm.org>
Date:	Wed, 02 Jun 2010 23:40:12 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	ebiederm@...stanetworks.com, randy.dunlap@...cle.com,
	gregkh@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kobject: Suppress compiler warning with gcc 3.x

Américo Wang <xiyou.wangcong@...il.com> writes:

> On Wed, Jun 02, 2010 at 11:02:28PM -0700, Eric W. Biederman wrote:
>>Américo Wang <xiyou.wangcong@...il.com> writes:
>>
>>> On Thu, Jun 03, 2010 at 07:31:41AM +0200, Eric Dumazet wrote:
>>>>Le jeudi 03 juin 2010 à 14:23 +0900, Tetsuo Handa a écrit :
>>>>> Gcc 3.x generates a warning
>>>>> 
>>>>>   include/linux/sysfs.h:183: warning: parameter has incomplete type
>>>>> 
>>>>> on each file.
>>>>> Suppress the warning by moving the definition of "enum kobj_ns_type"
>>>>> to before "#include <linux/sysfs.h>".
>>>>> 
>>>>> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
>>>>
>>>>
>>>>I was about to submit same patch, but I was also reverting 27eabc7cb4b3
>>>>(sysfs: Don't use enums in inline function declaration.)
>>>>
>>>>So that sysfs_exit_ns() prototype is consistent regardless of
>>>>CONFIG_SYSFS
>>>>
>>>>What do you think ?
>>>>
>>>
>>> This looks odd, in sysfs.h we do have a forward declaration of
>>> enum kobj_ns_type... I am wondering why gcc 3.x doesn't recognize it.
>>
>>Because the replacement is an inline, and we are passing the enum by value
>>gcc wants to see the full definition, at the point where the inline function
>>is declared.
>>
>
> But sysfs_exit_ns() is not inlined if CONFIG_SYSFS here.

You are right gcc 3.x seems full of it.  I was thinking of the !CONFIG_SYSFS
case where I had to pull out the enum because it is in fact inlined.

If we are going to worry about gcc 3.x and about my !CONFIG_SYSFS
inline function the clean way to handle this seems to be to introduce
a new header file that both sysfs.h and kobject.h can include.
Assuming/requiring that files that include sysfs.h also include
kobject.h to seems like the wrong way to go.

Eric

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