linux-kernel - Re: [PATCH -v4 2/2] printk: Add kernel parameter to control writes to /dev/kmsg

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Message-ID: <20160718090632.GD22689@nazgul.tnic>
Date:	Mon, 18 Jul 2016 11:06:32 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Dave Young <dyoung@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Franck Bui <fbui@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH -v4 2/2] printk: Add kernel parameter to control writes
 to /dev/kmsg

On Mon, Jul 18, 2016 at 04:17:12PM +0800, Dave Young wrote:
> Because IMHO it is wrong, they can not be ratelimited because the writing could
> be from different userspace programs.

It is ratelimited by interface openers.

> Simply ratelimiting different sources of writing is pointless to me.

So what are you arguing for? What is the *actual* *real-life* *use* case
you think will be handicapped?

> One can only see messages they would like to see by luck, it is worse
> than off.

THAT'S WHY YOU BOOT WITH "printk.devkmsg=on" TO SEE THEM ALL!

The /dev/kmsg thing was added for the more or less, wrong, historic
reasons and userspace started abusing it and interfering with kernel
operation. That's why we're adding this tristate option.

In the default case we're ratelimiting writes to it because they should
not interfere with kernel operation.

  [ Frankly, those writes are pretty much useless to the normal user so
    we can just as well ignore them but WTH. ]

So give me a concrete problem you see with the ralimiting and not some
notion of a feeling you might have of it being pointless, ok?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--