linux-kernel - Re: [PATCH 0/2][concept RFC] x86: BIOS-save kernel log to disk upon panic

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Message-ID: <4D3F095E.9000004@zytor.com>
Date:	Tue, 25 Jan 2011 09:33:18 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	"Ahmed S. Darwish" <darwish.07@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86-ML <x86@...nel.org>,
	Tony Luck <tony.luck@...el.com>, Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Willy Tarreau <wtarreau@...a.kernel.org>,
	Willy Tarreau <w@....eu>, Dirk Hohndel <hohndel@...radead.org>,
	Dirk.Hohndel@...el.com, IDE-ML <linux-ide@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 0/2][concept RFC] x86: BIOS-save kernel log to disk upon
 panic

On 01/25/2011 07:08 AM, Tejun Heo wrote:
> 
> There are holes but writing to them without full knowledge of the
> configuration can be quite dangerous.  I don't think it would be
> possible to mass deploy it without manual configuration unless we
> specifically reserve (and maybe mark) it in the filesystem.
> 

Reserve and mark in the filesystem is relatively straightforward, except
for btrfs, which doesn't have support for reserved extents.  This is a
bit of a shortcoming in btrfs.

>> All in one, a very intriguing idea IMO, and the hardest bits
>> (lowlevel x86 transition) is all implemented already.

Lowlevel x86 transition is not at all the hardest part.  It's
detail-oriented but well defined (and, I might add, incompletely
implemented -- 64 bits only, not using facilities we already have); the
*hard* part, and I mean harder by orders of magnitude, is to get the
BIOS to behave sanely without an intervening reboot, *AND* not trash
your data, ever.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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