linux-kernel - RE: [PATCH v3 1/2] vsprintf: Add %p[mM]U for uppercase MAC address

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Date:   Fri, 28 Apr 2023 07:46:14 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Rasmus Villemoes' <linux@...musvillemoes.dk>,
        Konrad Gräfe <k.graefe@...eware.de>,
        Quentin Schulz <quentin.schulz@...obroma-systems.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Felipe Balbi <balbi@...com>
CC:     "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v3 1/2] vsprintf: Add %p[mM]U for uppercase MAC address

From: Rasmus Villemoes
> Sent: 28 April 2023 07:57
> 
> On 27/04/2023 13.51, Konrad Gräfe wrote:
> > The CDC-ECM specification requires an USB gadget to send the host MAC
> > address as uppercase hex string. This change adds the appropriate
> > modifier.
> 
> Thinking more about it, I'm not sure this is appropriate, not for a
> single user like this. vsprintf() should not and cannot satisfy all
> possible string formatting requirements for the whole kernel. The %pX
> extensions are convenient for use with printk() and friends where one
> needs what in other languages would be "string interpolation" (because
> then the caller doesn't need to deal with temporary stack buffers and
> pass them as %s arguments), but for single items like this, snprintf()
> is not necessarily the right tool for the job.
> 
> In this case, the caller can just as well call string_upper() on the
> result, or not use sprintf() at all and do a tiny loop with
> hex_byte_pack_upper().

Or snprintf with "%02X:%02X:%02X:%02X:%02X:%02X".

	David

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