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

[heying (H)]

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.
> .