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

From: "Ahmed S. Darwish" <darwish.07@gmail.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: "Willy Tarreau" <wtarreau@hera.kernel.org>,
	"Dirk Hohndel" <hohndel@infradead.org>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	FBDEV-ML <linux-fbdev@vger.kernel.org>,
	IDE-ML <linux-ide@vger.kernel.org>,
	"Randy Dunlap" <rdunlap@xenotime.net>,
	"James Bottomley" <James.Bottomley@suse.de>,
	"H. Peter Anvin" <hpa@zytor.com>, X86-ML <x86@kernel.org>,
	"Ingo Molnar" <mingo@redhat.com>, "Ingo Molnar" <mingo@elte.hu>,
	"Jeff Garzik" <jgarzik@pobox.com>,
	"Peter Zijlstra" <a.p.zijlstra@chello.nl>,
	Dirk.Hohndel@intel.com, "Borislav Petkov" <bp@alien8.de>,
	"Dave Jones" <davej@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Mark Lord" <kernel@teksavvy.com>,
	"Arjan van de Ven" <arjan@infradead.org>,
	"Tony Luck" <tony.luck@intel.com>,
	KEXEC-ML <kexec@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Haren Myneni" <hbabu@us.ibm.com>,
	"Eric Biederman" <ebiederm@xmission.com>,
	"Tejun Heo" <tj@kernel.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Willy Tarreau" <w@1wt.eu>
Subject: Re: [PATCH 0/2][concept RFC] x86: BIOS-save kernel log to disk upon panic
Date: Thu, 27 Jan 2011 05:33:47 +0200	[thread overview]
Message-ID: <20110127033347.GA12477@laptop> (raw)
In-Reply-To: <20110127021338.GA20334@redhat.com>

(Very timely! was just exploring kexec-tools and friends)

On Wed, Jan 26, 2011 at 09:13:38PM -0500, Vivek Goyal wrote:
> On Wed, Jan 26, 2011 at 02:49:54PM +0200, Ahmed S. Darwish wrote:
> > 
> >   If not, can kexec be modified to do so? That possibly needs the help
> >   of a a bootloader extension.
> 
> - Generally kdump uses same kernel as first one. So if first kernel panics
>   then kdump kernel will also panic. Though one can keep a known good kdump
>   kernel.
> 

I was thinking of a 'special' kdump kernel: the older kernel will just pass
the physical RAM address of its ring buffer to the newer kernel. The newer
kernel will be __so specialized__ that it will just:

 - display the log in a friendly manner
 - write it to the swap partition
 - .. and halt

This way, I completely toss the BIOS while accomplishing similar goals.

>
> - Currently kexec-tools take care of loading the kdump kernel, and then
>   preparing memory map for second kernel and pass to it and also pass
>   along some information about vmcore in ELF headers to second kernel. 
>
> There is so much to it that I really don't think that modifying bootloaders to
> do all that might not trivial and more importantly I think it probably is not
> worth the effort.
> 

IMHO if done in a user-friendly and stable manner, it can really be worth
the effort. But quite honestly, since I did not read all the setup work
done by kexec-tools yet, I might be too optimistic.

> Thanks
> Vivek

thanks,

-- 
Darwish
http://darwish.07.googlepages.com

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