linux-kernel - Re: design: was: Re: [RFC PATCH v2] printk: console: Allow each console to have its own loglevel

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Message-ID: <87o7xz5su4.fsf@jogness.linutronix.de>
Date:   Fri, 08 Jul 2022 21:10:35 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>, Chris Down <chris@...isdown.name>
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>, kernel-team@...com
Subject: Re: design: was: Re: [RFC PATCH v2] printk: console: Allow each
 console to have its own loglevel

On 2022-07-08, Petr Mladek <pmladek@...e.com> wrote:
> The console-specific loglevel might be set by:
>
>   + "console=device,options/loglevel" kernel parameter at boot time

I ask if we avoid the use of "/loglevel" and instead use a generic
scheme of:

console=device,option,option,option

Of course, it would mean that the type of option would need to be
specified. Something like:

console=ttyS0,115200n8,loglevel=3

The reason why I make such a request is because I would like to be able
to support disabling threading for certain consoles. Something like:

console=ttyS0,115200n8,nothread

or when we have atomic consoles that we can specify that they are always
used with a "sync" option:

console=ttyS0,115200n8,sync

This is not the time to discuss what those strings should be. The point
is that we should use a syntax that allows adding more options for the
future.

Linus already [0] showed some approval to this method of option
extending as I suggested the "mute" option to have consoles keep quiet.

John Ogness

P.S. FWIW, I think this is a nice feature. I even mentioned it in my
LPC2019 printk talk, as there were previous efforts [1] to get this
feature implemented.

[0] https://lore.kernel.org/lkml/CAHk-=wif0QueN8ovkm_x7TsOgOHjRrOa4wU-zHgBP=FTAnzvNA@mail.gmail.com

[1] https://lore.kernel.org/lkml/bc1fe800930be76761b2bb4e6108fe5876a005c9.1491345440.git.calvinowens@fb.com