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

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Message-ID: <20200513121942.GK17734@linux-b0ei>
Date:   Wed, 13 May 2020 14:19:42 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Dmitry Safonov <dima@...sta.com>,
        Yafang Shao <laoar.shao@...il.com>
Subject: Re: [PATCH] printk: Add loglevel for "do not print to consoles".

On Wed 2020-05-13 20:24:24, Tetsuo Handa wrote:
> On 2020/05/13 19:49, Michal Hocko wrote:
> > On Wed 13-05-20 12:04:13, Petr Mladek wrote:
> >> What is so special about  OOM dump task so that it would deserve such
> >> complications?

> I don't think dump_tasks() is important information to be printed on consoles.
> But since somebody might think dump_tasks() is important information to be
> printed on consoles, I suggest switching KERN_NO_CONSOLES using e.g. sysctl.

You might achieve the same with DEBUG loglevel. Or do I miss anything?

> There is per-console loglevel proposal (which allows selecting "some" console
> backends). But it is based on KERN_$LOGLEVEL which is too rough-grained.

IMHO, developers already have troubles to decide between the existing
8 loglevels. And it is easier because the names describe the severity.

NO_CONSOLES would be different. The effect is almost[*] clear. But only
few people would know the background why it was introduced and where
to use it.

I know that it is meant as a modifier, like LOGLEVEL_SCHED and
KERN_CONT. But this is another reason to avoid it. We already have
huge pain with these two modifiers. They both do not work well.

[*] It will have no effect when it was disabled by a sysfs knob.

Best Regards,
Petr