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Subject: Re: [PATCH 1/2] hexdump: minimize the output width of the offset
To:     Randy Dunlap <rdunlap@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        John Ogness <john.ogness@linutronix.de>,
        linux-kernel@vger.kernel.org
Cc:     Zhen Lei <thunder.leizhen@huawei.com>
References: <20230805072116.1260-1-thunder.leizhen@huaweicloud.com>
 <20230805072116.1260-2-thunder.leizhen@huaweicloud.com>
 <41713c95-51a8-8e2a-9c70-dab10dacf26d@infradead.org>
 <8b7a579e-473d-ea90-58e0-e2f69f9bd002@huaweicloud.com>
 <adb341c7-f25a-5915-f63a-063aa8fc0978@infradead.org>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huaweicloud.com>
Message-ID: <7476190c-cf50-1b46-ef92-61ce97330956@huaweicloud.com>
Date:   Tue, 8 Aug 2023 10:54:47 +0800
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On 2023/8/8 10:42, Randy Dunlap wrote:
> 
> 
> On 8/7/23 18:10, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2023/8/8 6:37, Randy Dunlap wrote:
>>> Hi--
>>>
>>> On 8/5/23 00:21, thunder.leizhen@huaweicloud.com wrote:
>>>> From: Zhen Lei <thunder.leizhen@huawei.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@huawei.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.
> 
> Ah I see. My apologies.

It should be okay to move it into the case DUMP_PREFIX_OFFSET. The
compiler can optimize it.

> 
>>> Otherwise LGTM.
>>>
>>> Reviewed-by: Randy Dunlap <rdunlap@infradead.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