linux-kernel - Re: [PATCH 0/5] Persist printk buffer across reboots.

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Message-Id: <20120313151049.fa33d232.akpm@linux-foundation.org>
Date:	Tue, 13 Mar 2012 15:10:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Daniel Walker <dwalker@...o99.com>
Cc:	Avery Pennarun <apenwarr@...il.com>,
	Josh Triplett <josh@...htriplett.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	"David S. Miller" <davem@...emloft.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Fabio M. Di Nitto" <fdinitto@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Olaf Hering <olaf@...fle.de>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Tejun Heo <tj@...nel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Yinghai LU <yinghai@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 0/5] Persist printk buffer across reboots.

On Tue, 13 Mar 2012 10:08:51 -0700
Daniel Walker <dwalker@...o99.com> wrote:

> On Tue, Mar 13, 2012 at 01:36:36AM -0400, Avery Pennarun wrote:
> > The last patch in this series implements a new CONFIG_PRINTK_PERSIST option
> > that, when enabled, puts the printk buffer in a well-defined memory location
> > so that we can keep appending to it after a reboot.  The upshot is that,
> > even after a kernel panic or non-panic hard lockup, on the next boot
> > userspace will be able to grab the kernel messages leading up to it.  It
> > could then upload the messages to a server (for example) to keep crash
> > statistics.
> 
> There's currently driver/mtd/mtdoops.c, fs/pstore/, and
> drivers/staging/android/ram_console.c that do similar things
> as this. Did you investigate those for potentially modifying them to add
> this functionality ? If so what issues did you find?
> 
> I have a arm MSM G1 with persistent memory at 0x16d00000 size 20000bytes..
> It's fairly simple you just have to ioremap the memory, but then it's good
> for writing.. Currently the android ram_console uses this. How would I
> convert this area for use with your changes?

Yes, and various local implementations which do things such as stuffing
the log buffer into NVRAM as the kernel is crashing.

I do think we'd need some back-end driver arrangement which will permit
the use of stores which aren't in addressible mamory.

It's quite the can of worms, but definitely worth doing if we can get
it approximately correct.
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