linux-kernel - Re: [v2 1/5] arm64: kdump: reserve memory for crash dump kernel

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Date:	Mon, 11 May 2015 17:41:15 +0800
From:	Baoquan He <bhe@...hat.com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, hbabus@...ibm.com,
	linaro-kernel@...ts.linaro.org, geoff@...radead.org,
	catalin.marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, broonie@...nel.org,
	david.griego@...aro.org, kexec@...ts.infradead.org,
	vgoyal@...hat.com
Subject: Re: [v2 1/5] arm64: kdump: reserve memory for crash dump kernel

On 05/11/15 at 05:17pm, AKASHI Takahiro wrote:
> On 05/11/2015 04:54 PM, Baoquan He wrote:
> >In this patch you reserve a separate memory region in 1st kernel to
> >store elfcorehdr. I am wondering why you don't call add_buffer in
> >kexec-tools directly. Like this you can get a region from reserved
> >crashkernel region. Then you don't need reserve_elfcorehdr() to reserve
> >memory for elfcorehdr specifically. Like other ARCHs do only one memory
> >region is reserved in 1st kernel, that's crashkernel region.
> 
> I think that you misunderstand somewhat.
> * Kexec-tools only locates/identifies a small region for elfcore header within crash kernel's
> memory region while 1st kernel is running.
> * the data in elfcore header is filled up by kexec_load system call on 1st kernel.
> * 1st kernel doesn't reserve any region for elfcore header because the kernel
> commandline parameters don't contains "elfcorehdr=" parameter, then elfcorehdr_size=0.
> * Crash dump kernel does reserve the region, as I said, because we don't want to
> corrupt the info in elfcore header accidentally while crash kernel is running.
> 
> Clear?

OK, got it now.

Then I am wondering why "elfcorehdr=" can't be contained in kernel
cmdline as other ARCH does. Maybe I need go over all related threads
then know why it is. Thanks for explanation.

Thanks
Baoquan
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