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Date: Fri, 15 Dec 2000 23:48:57 +0100
From: "J . A . Magallon" <jamagallon@able.es>
To: Werner Almesberger <Werner.Almesberger@epfl.ch>
Cc: LA Walsh <law@sgi.com>, Alexander Viro <viro@math.psu.edu>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: Linus's include file strategy redux
Message-ID: <20001215234857.A689@werewolf.able.es>
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On 2000/12/15 Werner Almesberger wrote:
> LA Walsh wrote:
> 
> Exception: opaque types; there one would have to go via a __ identifier,
> i.e.
> 
> <public>/foo.h defines  struct __foo ...;
> <public>/bar.h includes <public>/foo.h
>                and uses #define FOOSIZE sizeof(struct __foo)
> <private>/foo.h either  typedef struct __foo foo_t;
>                 or      #define foo __foo  /* ugly */
> 

Easier: public kernel interfaces only work through pointers.
<public>/foo.h typedef struct foo foo_t;
               foo_t* foo_new();
<private>/foo.h includes <public>/foo.h
               struct foo { ............... };
               and uses #define FOOSIZE sizeof(foo_t)

Drawback: public access is slow (always through foo_set_xxxx_field(foo_t*))
          private access from kernel or modules is fast (foo_t->x = ...)
Advantage: kernel can change, foo_t internals can change and it is binary
          compatible. Even public headers can be kernel version
          independent.

Too kind-of-classroom-not-real-world-useless-thing ?
All depends on public access needing full fast paths...

-- 
Juan Antonio Magallon Lacarta                                 #> cd /pub
mailto:jamagallon@able.es                                     #> more beer

Linux werewolf 2.2.19-pre1 #1 SMP Fri Dec 15 22:25:20 CET 2000 i686

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