Re: [PATCH] printk: Add loglevel for "do not print to consoles".

From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org, Dmitry Safonov <dima@arista.com>,
	Michal Hocko <mhocko@suse.com>,
	Yafang Shao <laoar.shao@gmail.com>
Subject: Re: [PATCH] printk: Add loglevel for "do not print to consoles".
Date: Sat, 25 Apr 2020 10:07:45 +0900	[thread overview]
Message-ID: <842ff40b-a232-6098-4333-996a3033b30a@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20200425004609.GE8982@jagdpanzerIV.localdomain>

On 2020/04/25 9:46, Sergey Senozhatsky wrote:
> On (20/04/24 11:42), Tetsuo Handa wrote:
> [..]
>> @@ -19,6 +19,7 @@ static inline int printk_get_level(const char *buffer)
>>  		switch (buffer[1]) {
>>  		case '0' ... '7':
>>  		case 'c':	/* KERN_CONT */
>> +		case 'S':       /* KERN_NO_CONSOLES */
>>  			return buffer[1];
>>  		}
>>  	}
> 
> So this means NO_CONSOLES_AT_ALL, slow + fast ones.

Right.

>                                                     I wonder if this
> wants to be NO_SLOW_CONSOLES instead. Which then brings us to the
> next question - can this be done with per-console loglevel setting?

It is difficult to define what is slow consoles. While netconsole will be
a fast console, we can forward kernel messages via syslog daemon if desired.

NO_SLOW_CONSOLES might be useful for immediate notification like panic().
But KERN_NO_CONSOLES is not for immediate notification like panic().

KERN_NO_CONSOLES is for type of messages where "saved for later analysis" is
important but "printed for immediate notification" is not important.
In other words, KERN_NO_CONSOLES is NOT for dying messages where "printed for
immediate notification" is important.