Re: [PATCH v3 1/2] vsprintf: Add %p[mM]U for uppercase MAC address

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Fri, Apr 28, 2023 at 07:46:14AM +0000, David Laight wrote:
> 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".

Of course this is a step back. Why? Have you read actually what we have in %p
extensions already?

Also, what about stack?

Entire %pm/M exists due to reversed order. Otherwise it's an alias to %6phD or
alike.

-- 
With Best Regards,
Andy Shevchenko