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:

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On Fri, 2021-08-27 at 10:48 +0300, Andy Shevchenko wrote:

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On Thu, Aug 26, 2021 at 11:43:01AM -0700, Joe Perches wrote:

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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.

...

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+	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.

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+	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.