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

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Date:   Sat, 25 Apr 2020 01:10:15 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        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 2020/04/25 0:42, Steven Rostedt wrote:
> You can also use the tracing ring buffer for this, as it has been safe in
> all these contexts for a very long time. And that ring buffer is something
> that you can use outside of tracing (oprofile uses it).

Some messages are read from printk() source and other messages are read from
non-printk() source will loose ordering of messages (i.e. non-understandable
log files). For those who analyze log files, multiple sources are not acceptable.

> And both shouldn't be done within the kernel. The "CONSOLE_LOGLEVEL_SILENT"
> if for user decided policy, not the kernel making that policy for the user.

KERN_NO_CONSOLES is a mechanism for implementing user decided policy. As long as
userspace can control whether to use KERN_NO_CONSOLES (e.g. sysctl), there should
be no problem with adding KERN_NO_CONSOLES (i.e. this patch) to the kernel side.