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

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Message-ID:
 <PN3PR01MB9597D8AE22D48C7A5D351ABBB8BB2@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Tue, 22 Apr 2025 20:45:31 +0530
From: Aditya Garg <gargaditya08@...e.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Hector Martin <marcan@...can.st>, alyssa@...enzweig.io,
 Petr Mladek <pmladek@...e.com>, 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



On 22-04-2025 04:02 pm, Geert Uytterhoeven wrote:
> Hi Andy,
> 
> On Tue, 22 Apr 2025 at 12:16, Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
>> On Tue, Apr 22, 2025 at 10:43:59AM +0200, Geert Uytterhoeven wrote:
>>> On Tue, 22 Apr 2025 at 10:30, Aditya Garg <gargaditya08@...e.com> wrote:
>>>> On 22-04-2025 01:37 pm, Geert Uytterhoeven wrote:
>>>>> On Tue, 8 Apr 2025 at 08:48, Aditya Garg <gargaditya08@...e.com> wrote:
>>
>> ...
>>
>>>> Originally, it was %p4cr (reverse-endian), but on the request of the
>>>> maintainers, it was changed to %p4cn.
>>>
>>> Ah, I found it[1]:
>>>
>>> | so, it needs more information that this mimics htonl() / ntohl() for
>>> networking.
>>>
>>> IMHO this does not mimic htonl(), as htonl() is a no-op on big-endian.
>>> while %p4ch and %p4cl yield different results on big-endian.
>>>
>>>> So here network means reverse of host, not strictly big-endian.
>>>
>>> Please don't call it "network byte order" if that does not have the same
>>> meaning as in the network subsystem.
>>>
>>> Personally, I like "%p4r" (reverse) more...
>>> (and "%p4ch" might mean human-readable ;-)
>>
>> It will confuse the reader. h/r is not very established pair. If you really
>> wont see h/n, better to drop them completely for now then. Because I'm against
>> h/r pair.
> 
> I am not against h/n in se, but I am against bad/confusing naming.
> The big question is: should it print
>   (A) the value in network byte order, or
>   (B) the reverse of host byte order?
> 
> If the answer is (A), I see no real reason to have %p4n, as %p4b prints
> the exact same thing.  Moreover, it leaves us without a portable
> way to print values in reverse without the caller doing an explicit
> __swab32() (which is not compatible with the %p pass-by-pointer
> calling convention).
> 
> If the answer is (B), "%p4n using network byte order" is bad/confusing
> naming.

The answer is definitely (B). As far as bad/confusing naming is concerned,
I'll let vsprintf maintainers decide. As far as usage is concerned, %p4cl
is used in appletbdrm and %p4ch is used in to be upstreamed soon smc driver
by Asahi Linux.