linux-kernel - Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

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Date:	Fri, 04 Apr 2014 11:21:38 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Theodore Ts'o <tytso@....edu>, Joerg Roedel <joro@...tes.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mateusz Guzik <mguzik@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Kay Sievers <kay@...y.org>
Subject: Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

On 04/03/2014 10:05 AM, Theodore Ts'o wrote:
> On Thu, Apr 03, 2014 at 12:43:08PM +0200, Joerg Roedel wrote:
>>
>> How about just ignoring writes to /dev/kmsg altogether by default
>> (unless explicitly enabled in Kconfig or on the kernel cmdline)? Maybe I
>> am missing something but what are the legitimate use-cases for generally
>> allowing user-space to write into the kernel-log?
> 
> I'll give you one example which where /dev/kmesg is useful --- if you
> are running automated kernel tests, echoing "running test shared/127"
> .... several minutes later .... "running test shared/128", is very
> useful since if the kernel starts spewing warnings, or even
> oops/panics/livelocks, you know what test was running at the time of
> the failure.

I'm using /dev/kmsg in virtme so that I can easily capture, with
timestamps, the ten or so log lines that it produces.  It would be sad
if I had to worry about small ratelimits here.

/dev/kmsg is genuinely useful for the case where an initramfs wants to
log something (preferably only a little bit) and doesn't want to invent
a whole protocol for passing logging data through to the final logging
system.

The other thing I've used /dev/kmsg for is to shove a "I'm starting
something now" message in.  This is only really necessary because the
current kernel log timestamps are unusable crap.  (We could fix that,
hint hint.)

--Andy
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