linux-kernel - Re: [PATCH] linux++: delete some forward declarations

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Date: Thu, 13 Jun 2024 16:10:12 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@...il.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, linux-security-module@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] linux++: delete some forward declarations

On Thu, 13 Jun 2024 13:04:20 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Thu, 13 Jun 2024 15:34:02 -0400 Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Thu, 13 Jun 2024 22:22:18 +0300
> > Alexey Dobriyan <adobriyan@...il.com> wrote:
> >   
> > > g++ doesn't like forward enum declarations:
> > > 
> > > 	error: use of enum ‘E’ without previous declaration
> > > 	   64 | enum E;  
> > 
> > But we don't care about g++. Do we?  
> 
> It appears that g++ is a useful enum declaration detector.
> 
> I'm curious to know how even the above warning was generated.  Does g++
> work at all on Linux?
> 
> > I would make that a separate patch.  
> 
> What are you referring to here?

The enum change should be separate from the struct changes.

> 
> > > 
> > > Delete those which aren't used.
> > > 
> > > Delete some unused/unnecessary forward struct declarations for a change.  
> > 
> > This is a clean up, but should have a better change log. Just something
> > simple like:
> > 
> >   Delete unnecessary forward struct declarations.  
> 
> Alexey specializes in cute changelogs.

eh

> 
> I do have a concern about the patch: has it been tested with all
> possible Kconfigs?  No.  There may be some configs in which the forward
> declaration is required.
> 
> And...  I'm a bit surprised that forward declarations are allowed in C.
> A billion years ago I used a C compiler which would use 16 bits for
> an enum if the enumted values would fit in 16 bits.  And it would use 32
> bits otherwise.  So the enumerated values were *required* for the
> compiler to be able to figure out the sizeof.  But it was a billion
> years ago.

Well, I only looked at the one change in ftrace.h which has a
"struct seq_file;" that is not used anywhere else in the file, so that
one definitely can go.

-- Steve