linux-kernel - Re: [PATCH v4 1/3] lib/vsprintf: Add support for generic FourCCs by extending %p4cc

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Message-ID: <CAMuHMdUUkhJm++zitVRQdSHJUo9McjYGeVz4Frv2sct_Can+aw@mail.gmail.com>
Date: Wed, 23 Apr 2025 19:46:39 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Petr Mladek <pmladek@...e.com>, Aditya Garg <gargaditya08@...e.com>, 
	Hector Martin <marcan@...can.st>, alyssa@...enzweig.io, Sven Peter <sven@...npeter.dev>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Aun-Ali Zaidi <admin@...eit.net>, 
	Maxime Ripard <mripard@...nel.org>, airlied@...hat.com, Simona Vetter <simona@...ll.ch>, 
	Steven Rostedt <rostedt@...dmis.org>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Sergey Senozhatsky <senozhatsky@...omium.org>, Jonathan Corbet <corbet@....net>, 
	Andrew Morton <akpm@...ux-foundation.org>, apw@...onical.com, joe@...ches.com, 
	dwaipayanray1@...il.com, lukas.bulwahn@...il.com, Kees Cook <kees@...nel.org>, 
	tamird@...il.com, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
	dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org, 
	Asahi Linux Mailing List <asahi@...ts.linux.dev>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] lib/vsprintf: Add support for generic FourCCs by
 extending %p4cc

Hi Andy,

On Wed, 23 Apr 2025 at 18:30, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> On Wed, Apr 23, 2025 at 04:50:02PM +0200, Geert Uytterhoeven wrote:
> > On Wed, 23 Apr 2025 at 15:39, Petr Mladek <pmladek@...e.com> wrote:
> > > On Tue 2025-04-22 10:43:59, Geert Uytterhoeven wrote:
>
> ...
>
> > > The problem is that the semantic is not the same. The modifiers affect
> > > the output ordering of IPv4 addresses while they affect the reading order
> > > in case of FourCC code.
> >
> > Note that for IPv4 addresses we have %pI4, which BTW also takes [hnbl]
> > modifiers.
>
> Ouch, now I think I understand your complain. You mean that the behaviour of
> h/n here is different to what it is for IPv4 case?

Indeed. "%pI4n" byte-swaps on little-endian, but not on big-endian
(remember, network byte-order _is_ big-endian), while "%p4cn" swaps
everywhere.

> > > Avoid the confusion by replacing the "n" modifier with "hR", aka
> > > reverse host ordering.
>
> Not ideal, but better than 'h'ost / 'r'everse pair. Not giving a tag and not
> objecting either if there is a consensus.

That is worth as much as my LGTM ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds