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

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Date:	Tue, 13 Mar 2012 19:19:06 -0700
From:	Daniel Walker <dwalker@...o99.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, Seiji Aguchi <seiji.aguchi@....com>
Subject: Re: [PATCH 0/5] Persist printk buffer across reboots.

On Tue, Mar 13, 2012 at 03:10:49PM -0700, Andrew Morton wrote:
> 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.

For sure.. I've had at least a couple non-OOPS based crashed I would
have liked to get logs for.

There is also this series,

http://lists.infradead.org/pipermail/kexec/2011-July/005258.html

It seems awkward that pstore is in fs/pstore/ then pstore ends up as the
"back end" where it could just be the whole solution.

Daniel
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