linux-kernel - Re: [PATCH] printk: allow setting DEFAULT_MESSAGE

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Date:	Thu, 27 Jan 2011 07:57:54 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Mandeep Singh Baines <msb@...omium.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	olofj@...omium.org
Subject: Re: [PATCH] printk: allow setting DEFAULT_MESSAGE_LEVEL via Kconfig

Alexey Dobriyan (adobriyan@...il.com) wrote:
> On Wed, Jan 26, 2011 at 03:10:17PM -0800, Andrew Morton wrote:
> > On Wed, 26 Jan 2011 14:57:03 -0800
> > Randy Dunlap <rdunlap@...otime.net> wrote:
> > 
> > > > I'm a bit surprised that this wasn't already tunable at boot-time
> > > > and/or at runtime.
> > > 
> > > 
> > > As WANG Cong replied:
> > > 
> > > Why? We already have "loglevel=" kernel parameter.
> > 
> > That's different.
> > 
> > Mandeep's patch addresses printks which didn't have a facility level. 
> 
> For those, we have ignore_loglevel kernel parameter.

That's a little different. ignore_loglevel will print ALL kernel messages
to the console. What we would like to do is look at all messages that
are KERN_WARNING (and higher in priority) very closely. Bugs lie there;)
Problem is that DEFAULT_MESSAGE_LEVEL is KERN_WARNING so there is too
much noise at KERN_WARNING. So we'd like to be able to set
DEFAULT_MESSAGE_LEVEL (default_message_loglevel) to something lower in,
priority, at boot or earlier. You can set it via /proc/sys/kernel/printk
(takes an int_vec) but that's too late. A ton of stuff has already been
logged by the time we're able to change a sysctl.

Our plan is to whitelist any KERN_WARNING messages we know are OK and
flag any new KERN_WARNING messages. We're hoping this will help us cut
down on regressions. We've been burned in the past where we caused a
regression which tooks weeks to locate and triage only to later learn
that there was a new KERN_WARNING that if we hadn't ignored would have
caught the bug much much earlier.
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