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

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Date:	Mon, 18 Jul 2016 15:38:45 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Borislav Petkov <bp@...en8.de>
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 07/18/16 at 09:21am, Borislav Petkov wrote:
> On Mon, Jul 18, 2016 at 01:20:32PM +0800, Dave Young wrote:
> > Sorry, seems I do not get your point, suppose using the bis defined in your
> > patch, shouldn't below work?
> 
> When you supply "printk.devkmsg=" on the kernel command line, then
> devkmsg logging setting is final for the current boot because we lock it
> with DEVKMSG_LOG_MASK_LOCK, see control_devkmsg() here:

Boris, I saw that point and I agreed about that design, what I do not like is
the ratelimit part. What in my mind is like below (suppose default=off)

printk.devkmsg= on kernel cmdline
   -> locked, one can not use sysctl to change it
   -> follow the kernel cmdline setting
no printk.devkmsg= on kernel cmdline
   -> unlocked, default is off, writing to /dev/kmsg is forbidded
      -> usespace set sysctl printk.devkmsg=on
         -> writing to /dev/kmsg is allowed.

Thanks
Dave