linux-kernel - Re: [PATCH next 1/1] lib: Optimise hex_dump_to

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Message-ID: <Z7JO9eutvu3KBEbc@smile.fi.intel.com>
Date: Sun, 16 Feb 2025 22:47:49 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: David Laight <david.laight.linux@...il.com>
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH next 1/1] lib: Optimise hex_dump_to_buffer()

On Sun, Feb 16, 2025 at 08:19:01PM +0000, David Laight wrote:
> Fastpath the normal case of single byte output that fits in the buffer.
> Output byte groups (byteswapped on little-endian) without calling snprintf().
> Remove the restriction that rowsize must be 16 or 32.
> Remove the restriction that groupsize must be 8 or less.
> If groupsize isn't a power of 2 or doesn't divide into both len and
>   rowsize it is set to 1 (otherwise byteswapping is hard).
> Change the types of the rowsize and groupsize parameters to be unsigned types.

> Tested in a userspace harness, code size (x86-64) halved to 723 bytes.

Does it imply running the respective test cases we have?
Do you need to add more test cases? I believe so.
Without test cases added it's a no go.

> +extern size_t hex_dump_to_buffer(const void *buf, size_t len, size_t rowsize,
> +			      size_t groupsize, char *linebuf,
> +			      size_t linebuflen, bool ascii);

Looking at another thread where upper layer function wants to have unsigned
long flags instead of bool ascii, I would also do the new API, that takes flags
and leave the old one as a simple wrapper with all restrictions being applied.

And again, provide it together with a bunch of test cases.

...

> +			dst[0] = hex_asc_hi(ch);
> +			dst[1] = hex_asc_lo(ch);

We have hex_pack_byte() or so

...

> +			ch = ptr[j ^ byteswap];
> +			dst[0] = hex_asc_hi(ch);
> +			dst[1] = hex_asc_lo(ch);
> +			dst += 2;

Ditto.

...

> -		linebuf[lx++] = (isascii(ch) && isprint(ch)) ? ch : '.';
> +		*dst++ = ch >= ' ' && ch < 0x7f ? ch : '.';

Please also add a test case for this to make sure it has no changes.

-- 
With Best Regards,
Andy Shevchenko