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

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Message-ID: <20200427062117.GC486@jagdpanzerIV.localdomain>
Date:   Mon, 27 Apr 2020 15:21:17 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Dmitry Safonov <dima@...sta.com>,
        Michal Hocko <mhocko@...e.com>,
        Yafang Shao <laoar.shao@...il.com>
Subject: Re: [PATCH] printk: Add loglevel for "do not print to consoles".

On (20/04/25 10:07), Tetsuo Handa wrote:
> 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.

Yes, there is no universal definition for "fast" and "slow" console and
I'm not suggesting to come with such a definition.

> 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.

per-console loglevel is a user configurable parameter.
KERN_NO_CONSOLES is a hard-coded policy.

	-ss