linux-kernel - Re: [PATCH v2] printk: make sure to print log on console.

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Date:   Wed, 20 Jun 2018 10:55:25 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Maninder Singh <maninder1.s@...sung.com>,
        sergey.senozhatsky@...il.com, rostedt@...dmis.org,
        linux-kernel@...r.kernel.org, a.sahrawat@...sung.com,
        pankaj.m@...sung.com, v.narang@...sung.com
Subject: Re: [PATCH v2] printk: make sure to print log on console.

On (06/19/18 12:52), Petr Mladek wrote:
> > But when I set /sys/module/printk/parameters/ignore_loglevel I naturally
> > expect it to take an immediate action. Without waiting for the consoles
> > to catch up and to discard N messages [if the consoles were behind the
> > logbuf head].
> 
> Yeah, I understand this view. I thought about it as well. But did you
> ever needed this behavior in the real life?
>
> I personally changed ignore_loglevel only before I wanted to reproduce a
> bug. Then it would be perfectly fine to handle it only in
> vprintk_emit(). In fact, it would be even better because it would
> affect only messages that happened after I triggered the bug.

I thought that additionally to sysfs knob we had a console_foo() function
that simply set ignore_loglevel. But it appears to be sysfs or boot-time
configurable only. I confused CONSOLE_LOGLEVEL_MOTORMOUTH and ignore_loglevel
and thought that a console_verbose() call would basically set ignore_loglevel
to true. It's a bit misleading that we have multiple and independent ways of
achieving the same result.

So maybe the patch can stand the way it is, after all. JFI, still haven't
seen those "helps in real life a lot" examples, tho.

> schizophrenic logic.

OUCH! Seriously, what the... Knock it off!

	-ss