linux-kernel - Re: [PATCH v2 2/3] lib/vsprintf: Split out sprintf() and friends

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Message-ID: <ZNoM/LUhjG2/NHl1@smile.fi.intel.com>
Date:   Mon, 14 Aug 2023 14:16:12 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Petr Mladek <pmladek@...e.com>, Marco Elver <elver@...gle.com>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, Sergey Senozhatsky <senozhatsky@...omium.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 2/3] lib/vsprintf: Split out sprintf() and friends

On Fri, Aug 11, 2023 at 03:28:17PM -0400, Steven Rostedt wrote:
> On Thu, 10 Aug 2023 16:17:57 +0200
> Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
> 
> > > Btw, it's easy to enforce IIUC, i.e. by dropping
> > > 
> > >   #ifndef _FOO_H
> > >   #define _FOO_H
> > >   #endif
> > > 
> > > mantra from the headers.
> > 
> > No, you can't do that, because some headers legitimately include other
> > headers, often for type definitions. Say some struct definition where
> > one of the members is another struct (struct list_head being an obvious
> > example). Or a static inline function.
> > 
> > We _also_ don't want to force everybody who includes a.h to ensure that
> > they first include b.h because something in a.h needs stuff from b.h.
> > 
> > So include guards must be used. They are a so well-known idiom that gcc
> > even has special code for handling them: If everything in a foo.h file
> > except comments is inside an ifndef/define/endif, gcc remembers that
> > that foo.h file has such an include guard, so when gcc then encounters
> > some #include directive that would again resolve to that same foo.h, and
> > the include guard hasn't been #undef'ed, it doesn't even do the syscalls
> > to open/read/close the file again.
> 
> I hope Andy was just joking with that recommendation.

Too radical to be true to implement. But it's always good to have a rationale
(thanks Rasmus) behind existing approach.

-- 
With Best Regards,
Andy Shevchenko