linux-kernel - Re: [PATCH 1/2] hexdump: minimize the output width of the offset

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Date:   Mon, 7 Aug 2023 15:37:19 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     thunder.leizhen@...weicloud.com, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        linux-kernel@...r.kernel.org
Cc:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: Re: [PATCH 1/2] hexdump: minimize the output width of the offset

Hi--

On 8/5/23 00:21, thunder.leizhen@...weicloud.com wrote:
> From: Zhen Lei <thunder.leizhen@...wei.com>
> 
> The offset of case DUMP_PREFIX_OFFSET always starts from 0. Currently,
> the output width is fixed to 8. But we usually dump only tens or hundreds
> of bytes, occasionally thousands of bytes. Therefore, the output offset
> value always has a number of leading zeros, which increases the number of
> bytes printed and reduces readability. Let's minimize the output width of
> the offset based on the number of significant bits of its maximum value.
> 
> Before:
> dump_size=36:
> 00000000: c0 ba 8c 80 00 80 ff ff 6c 93 ee 2f ee bf ff ff
> 00000010: 00 50 1e 98 ff 27 ff ff 01 00 00 00 00 00 00 00
> 00000020: 80 ca 2f 98
> 
> After:
> dump_size=8:
> 0: c0 ba 89 80 00 80 ff ff
> 
> dump_size=36:
> 00: c0 3a 91 80 00 80 ff ff 6c 93 ae 76 30 ce ff ff
> 10: 00 60 cd 60 7d 4e ff ff 01 00 00 00 00 00 00 00
> 20: 40 9e 29 40
> 
> dump_size=300:
> 000: c0 ba 8d 80 00 80 ff ff 6c 93 ce d4 78 a7 ff ff
> 010: 00 00 16 18 0c 40 ff ff 01 00 00 00 00 00 00 00
> 020: 01 00 00 00 00 00 00 00 e8 bc 8d 80 00 80 ff ff
> ... ...
> 110: 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 120: 00 08 12 01 0c 40 ff ff 00 00 01 00
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> ---
>  lib/hexdump.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/hexdump.c b/lib/hexdump.c
> index 06833d404398d74..86cb4cc3eec485a 100644
> --- a/lib/hexdump.c
> +++ b/lib/hexdump.c
> @@ -263,12 +263,21 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
>  		    const void *buf, size_t len, bool ascii)
>  {
>  	const u8 *ptr = buf;
> -	int i, linelen, remaining = len;
> +	int i, linelen, width = 0, remaining = len;
>  	unsigned char linebuf[32 * 3 + 2 + 32 + 1];
>  
>  	if (rowsize != 16 && rowsize != 32)
>  		rowsize = 16;
>  
> +	if (prefix_type == DUMP_PREFIX_OFFSET) {
> +		unsigned long tmp = len - 1;	/* offset start from 0, so minus 1 */
> +
> +		do {
> +			width++;
> +			tmp >>= 4;
> +		} while (tmp);
> +	}
> +

You could put all of that ^^^ in the case DUMP_PREFIX_OFFSET below.
Otherwise LGTM.

Reviewed-by: Randy Dunlap <rdunlap@...radead.org>
Thanks.

>  	for (i = 0; i < len; i += rowsize) {
>  		linelen = min(remaining, rowsize);
>  		remaining -= rowsize;
> @@ -282,7 +291,7 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
>  			       level, prefix_str, ptr + i, linebuf);
>  			break;
>  		case DUMP_PREFIX_OFFSET:
> -			printk("%s%s%.8x: %s\n", level, prefix_str, i, linebuf);
> +			printk("%s%s%0*x: %s\n", level, prefix_str, width, i, linebuf);
>  			break;
>  		default:
>  			printk("%s%s%s\n", level, prefix_str, linebuf);

-- 
~Randy