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

From: AKASHI Takahiro
Date: Tue May 12 2015 - 03:32:55 EST

On 05/11/2015 06:41 PM, Baoquan He wrote:
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.


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.

Kexec-tools on 1st kernel appends "elfcorehdr=" to the kernel command line,
actually chosen/bootargs in a device tree, that is passed to *crash dump kernel*.
So when crash dump kernel boots up, it can recognizes that area (and reserves it
for later use of managing /proc/vmcore.)

-Takahiro AKASHI


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