Message-ID: <5551AC97.9040802@linaro.org>
Date: Tue, 12 May 2015 16:32:39 +0900
From: AKASHI Takahiro <takahiro.akashi@linaro.org>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0
MIME-Version: 1.0
To: Baoquan He <bhe@redhat.com>
CC: linux-arm-kernel@lists.infradead.org, hbabus@us.ibm.com,
        linaro-kernel@lists.linaro.org, geoff@infradead.org,
        catalin.marinas@arm.com, will.deacon@arm.com,
        linux-kernel@vger.kernel.org, broonie@kernel.org,
        david.griego@linaro.org, kexec@lists.infradead.org, vgoyal@redhat.com
Subject: Re: [v2 1/5] arm64: kdump: reserve memory for crash dump kernel
References: <1429861989-8417-1-git-send-email-takahiro.akashi@linaro.org> <1429861989-8417-2-git-send-email-takahiro.akashi@linaro.org> <20150428091935.GJ15033@dhcp-16-116.nay.redhat.com> <55505C91.8070503@linaro.org> <20150511075447.GA4290@dhcp-128-28.nay.redhat.com> <5550659D.90006@linaro.org> <20150511094115.GB4290@dhcp-128-28.nay.redhat.com>
In-Reply-To: <20150511094115.GB4290@dhcp-128-28.nay.redhat.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1975
Lines: 43

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.
>>
>> 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.

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.)

Thanks,
-Takahiro AKASHI

> Thanks
> Baoquan
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/