linux-kernel - Re: [PATCH 1/5] vsprintf/Documentation: Add X to %*ph extension to output upper case hex

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Date:   Fri, 27 Aug 2021 19:49:24 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] vsprintf/Documentation: Add X to %*ph extension to
 output upper case hex

On Fri, 2021-08-27 at 11:49 +0300, Andy Shevchenko wrote:
> On Fri, Aug 27, 2021 at 01:08:10AM -0700, Joe Perches wrote:
> > On Fri, 2021-08-27 at 10:48 +0300, Andy Shevchenko wrote:
> > > On Thu, Aug 26, 2021 at 11:43:01AM -0700, Joe Perches wrote:
> > > > A few sysfs output uses of hex arrays are uppercase and are nominally ABI.
> > > > 
> > > > Add a mechanism to the existing vsprintf %*ph hex output extension to
> > > > support upper case hex output.
> > > 
> > > ...
> > > 
> > > > +	The preferred output is lowercase
> > > >  	%*ph	00 01 02  ...  3f
> > > >  	%*phC	00:01:02: ... :3f
> > > >  	%*phD	00-01-02- ... -3f
> > > >  	%*phN	000102 ... 3f
> > > > +	Formats with X are uppercase, used for backwards compatibility
> > > > +	%*phX	00 01 02  ...  3F
> > > > +	%*phCX	00:01:02: ... :3F
> > > > +	%*phDX	00-01-02- ... -3F
> > > > +	%*phNX	000102 ... 3F
> > > 
> > > Why not using %*pH...?
> > 
> > I find X more intelligible.
> > 
> > > > +	char locase = 0x20;	/* ASCII OR'd for lower case see: number() */
> > > 
> > > If you use h vs H, you may derive this from (fmt[...] & SMALL).
> > 
> > It's not necessary to use any more of the rather limited vsprintf
> > extension namespace.
> 
> I understand your concern, but %*ph is quite widely used (I guess top 1 or 2
> among all %p extensions),

Cumulatively 3rd after %pM and %pOF

> its performance degradation with your code may affect
> a lot of other users and hence a kernel as a whole.
> 
> So, that's why my proposal stays.

Knock yourself out.

> Of course you may provide a benchmark (btw, where are the test cases for this?)

You are welcome to provide both test cases and benchmarks.
I find the whole thing rather dull.

> for yours and mine variant and we will see if it makes sense to optimize.

It doesn't.  Anyone thinking there is a required printf/vsprintf
optimization in the kernel is decidedly barking up the wrong tree.