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

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Date:   Tue, 8 Aug 2023 09:10:05 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...weicloud.com>
To:     Randy Dunlap <rdunlap@...radead.org>,
        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



On 2023/8/8 6:37, Randy Dunlap wrote:
> 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.

for (i = 0; i < len; i += rowsize) {

"case DUMP_PREFIX_OFFSET" is in the loop, and moving the code above
to the case DUMP_PREFIX_OFFSET will be calculate multiple times. But
following your prompt, I thought again, I can control it with the
local variable width. I will post v2 right away.

> 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);
> 

-- 
Regards,
  Zhen Lei