linux-kernel - Re: [PATCH v2] smp: kernel/panic.c

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Date:   Fri, 19 Mar 2021 09:39:50 +0800
From:   "heying (H)" <heying24@...wei.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Peter Zijlstra <peterz@...radead.org>
CC:     Ingo Molnar <mingo@...nel.org>, <frederic@...nel.org>,
        <paulmck@...nel.org>, <clg@...d.org>, <qais.yousef@....com>,
        <johnny.chenyi@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] smp: kernel/panic.c - silence warnings

Dear Ingo, Peter and Christophe,


I'm a bit confused. All of you have a good reason but have opposite 
opinions.

If I don't add 'extern', can you accept it? Please let me know.


Thanks,

He Ying

在 2021/3/18 13:53, Christophe Leroy 写道:
>
>
> Le 17/03/2021 à 18:37, Peter Zijlstra a écrit :
>> On Wed, Mar 17, 2021 at 06:17:26PM +0100, Christophe Leroy wrote:
>>>
>>>
>>> Le 17/03/2021 à 13:23, Peter Zijlstra a écrit :
>>>> On Wed, Mar 17, 2021 at 12:00:29PM +0100, Christophe Leroy wrote:
>>>>> What do you mean ? 'extern' prototype is pointless for function 
>>>>> prototypes
>>>>> and deprecated, no new function prototypes should be added with 
>>>>> the 'extern'
>>>>> keyword.
>>>>>
>>>>> checkpatch.pl tells you: "extern prototypes should be avoided in 
>>>>> .h files"
>>>>
>>>> I have a very strong preference for extern on function decls, to match
>>>> the extern on variable decl.
>>>
>>> You mean you also do 'static inline' variable declarations ?
>>
>> That's a func definition, not a declaration. And you _can_ do static
>> variable definitions in a header file just fine, although that's
>> typically not what you'd want. Although sometimes I've seen people do:
>>
>> static const int my_var = 10;
>>
>> inline is an attribute that obviously doesn't work on variables.
>>
>>> Using the extern keyword on function prototypes is superfluous visual
>>> noise so suggest removing it.
>>
>> I don't agree; and I think the C spec is actually wrong there (too).
>>
>> The thing is that it distinguishes between a forward declaration of a
>> function in the same TU and an external declaration for a function in
>> another TU.
>>
>> That is; if I see:
>>
>> void ponies(int legs);
>>
>> I expect that function to be defined later in the same TU. IOW it's a
>> forward declaration. OTOH if I see:
>>
>> extern void ponies(int legs);
>>
>> I know I won't find it in this TU and the linker will end up involved.
>
> Yes I can understand that for a .c file where you want to distinguish 
> between forward declaration of functions defined in the file and 
> functions declared outside. There, it is definitely an added value.
>
> But in .h, all functions must be defined somewhere else, otherwise you 
> have another problem. So all functions would have the 'extern' keyword 
> according to your reasoning. Therefore that's just useless and I fully 
> agree with Checkpatch's commit that in that case that's "superfluous 
> visual noise" impeding readability and making it more difficult to fit 
> the prototype on a single line.
>
>
>>
>> Now, the C people figured that distinction was useless and allowed
>> sloppiness. But I still think there's merrit to that. And as mentioned
>> earlier, it is consistent with variable declarations.
>>
> .