linux-kernel - Re: [PATCH 01/30] headers: fixup cred.h, ipc

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Date:	Fri, 10 Apr 2009 17:17:01 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	akpm@...ux-foundation.org, containers@...ts.linux-foundation.org,
	xemul@...allels.com, serue@...ibm.com, dave@...ux.vnet.ibm.com,
	orenl@...columbia.edu, hch@...radead.org,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/30] headers: fixup cred.h, ipc_namespace.h

On Fri, Apr 10, 2009 at 10:47:47AM +0200, Ingo Molnar wrote:
> 
> * Alexey Dobriyan <adobriyan@...il.com> wrote:

> > +struct kern_ipc_perm;

> Please, not yet another forward declaration...
> 
> I believe this should be cleaned up properly, instead of sprinkling 
> the kernel with random placed forward declarations.

It's at the top of the file, there is no random placing going on.

> In a cleanly structured piace of code there's rarely any need for 
> forward declarations like this. There's two basic header types 
> needed:
> 
>    foo_types.h       declares all the data types and constants
>                      [no complex inline functions]
> 
>    foo.h             externs, complex inlines
> 
> foo.h includes all foo_types.h and bar_types.h headers it needs.
> 
> The foo_types.h file includes all other bar_types.h headers it 
> depends on for its data type definitions.
> 
> foo_types.h never includes a bar.h file.

This can be viewed as bad precedent created by mm_types.h.

Look how many headers mm_types.h includes. It doesn't change much
if one includes mm.h or mm_types.h.

Look how many places includes spinlock_types.h

> The end result will be a clean hieararchy of data types, separated 
> from methods. Complex inlines dont create the incestous 
> cross-dependency hell anymore and dont contaminate the foo_types.h 
> files.
> 
> Yes, this is quite a bit of work, but this has been done before for 
> several complex headers so it's possible to do it.

Forward declarations are currently well established.

Want to change rules? Fine, do it.
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