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

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Message-ID: <CAHqTa-3DiZhd_yoRTzp2Np0Rp=_zrfL7CbN_twu+ZZeu7f4ENg@mail.gmail.com>
Date:	Tue, 13 Mar 2012 02:00:30 -0400
From:	Avery Pennarun <apenwarr@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	akpm@...ux-foundation.org, josh@...htriplett.org,
	paulmck@...ux.vnet.ibm.com, mingo@...e.hu, a.p.zijlstra@...llo.nl,
	fdinitto@...hat.com, hannes@...xchg.org, olaf@...fle.de,
	paul.gortmaker@...driver.com, tj@...nel.org, hpa@...ux.intel.com,
	yinghai@...nel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 0/5] Persist printk buffer across reboots.

On Tue, Mar 13, 2012 at 1:53 AM, David Miller <davem@...emloft.net> wrote:
> From: Avery Pennarun <apenwarr@...il.com>
> Date: Tue, 13 Mar 2012 01:36:36 -0400
>
>> 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.
>
> On some platforms there are formal ways to reserve areas of memory
> such that the bootup firmware will know to not touch it on soft resets
> no matter what.  For example, on Sparc there are OpenFirmware calls to
> set aside such an area of soft-reset preserved memory.
>
> I think some formal agreement with the system firmware is a lot better
> when available, and should be explicitly accomodated in these changes
> so that those of us with such facilities can very easily hook it up.

Sounds good to me.  Do you have any pointers?  Just use an
early_param?  If we see the early_param but we can't reserve the
requested address, should we fall back to probing or disable the
PRINTK_PERSIST mode entirely?

Thanks,

Avery
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