linux-kernel - Re: [PATCH] printk: Add caller information to printk() output.

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Message-ID: <be668360-279b-5c24-4fc1-10ef050bd87f@i-love.sakura.ne.jp>
Date:   Tue, 4 Dec 2018 19:16:56 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>, Dmitry Vyukov <dvyukov@...gle.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] printk: Add caller information to printk() output.

On 2018/12/04 11:02, Sergey Senozhatsky wrote:
> On (12/02/18 20:23), Tetsuo Handa wrote:
>>
>> Some examples for console output:
>>
>>   [    0.919699]@T1 x86: Booting SMP configuration:
>>   [    4.152681]@T271 Fusion MPT base driver 3.04.20
>>   [    5.070470]@C0 random: fast init done
>>   [    6.587900]@C3 random: crng init done
> 
> This is hard to read. Let's have a fixed width space for from_id.

Console might be only 80 columns. When we have to check from screen capture of
crash, triggering needless newlines due to occupying columns more than needed
will not be nice. Also, syzbot has file size limit for saving console output.
Wasting with needless spaces increases possibility of loosing past lines.
Given that said, do you still want to waste precious columns with spaces?

> 
>> +config PRINTK_FROM
>> +	bool "Show caller information on printks"
>> +	depends on PRINTK
> 
> Wasn't it supposed to also depend on DEBUG_AID_FOR_SYZBOT?

CONFIG_DEBUG_AID_FOR_SYZBOT is currently linux-next only option.
This feature will be useful for non-syzbot environments.