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

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Message-ID: <202504081456.31AF24D2F7@keescook>
Date: Tue, 8 Apr 2025 14:56:24 -0700
From: Kees Cook <kees@...nel.org>
To: Aditya Garg <gargaditya08@...e.com>
Cc: alyssa@...enzweig.io, Petr Mladek <pmladek@...e.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.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,
	tamird@...il.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org,
	Hector Martin <marcan@...can.st>,
	Asahi Linux Mailing List <asahi@...ts.linux.dev>
Subject: Re: [PATCH v4 1/3] lib/vsprintf: Add support for generic FourCCs by
 extending %p4cc

On Tue, Apr 08, 2025 at 12:17:57PM +0530, Aditya Garg wrote:
> From: Hector Martin <marcan@...can.st>
> 
> %p4cc is designed for DRM/V4L2 FourCCs with their specific quirks, but
> it's useful to be able to print generic 4-character codes formatted as
> an integer. Extend it to add format specifiers for printing generic
> 32-bit FourCCs with various endian semantics:
> 
> %p4ch	Host byte order
> %p4cn	Network byte order
> %p4cl	Little-endian
> %p4cb	Big-endian
> 
> The endianness determines how bytes are interpreted as a u32, and the
> FourCC is then always printed MSByte-first (this is the opposite of
> V4L/DRM FourCCs). This covers most practical cases, e.g. %p4cn would
> allow printing LSByte-first FourCCs stored in host endian order
> (other than the hex form being in character order, not the integer
> value).
> 
> Acked-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> Tested-by: Petr Mladek <pmladek@...e.com>
> Signed-off-by: Hector Martin <marcan@...can.st>

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook