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Subject: Re: [PATCH 1/2 v2] kdump: add the vmcoreinfo documentation
To:     Dave Young <dyoung@redhat.com>
Cc:     Borislav Petkov <bp@alien8.de>, linux-kernel@vger.kernel.org,
        kexec@lists.infradead.org, tglx@linutronix.de, mingo@redhat.com,
        x86@kernel.org, akpm@linux-foundation.org, bhe@redhat.com,
        Jonathan Corbet <corbet@lwn.net>, linux-doc@vger.kernel.org,
        Kazuhito Hagio <k-hagio@ab.jp.nec.com>
References: <20181202030839.29945-1-lijiang@redhat.com>
 <20181202030839.29945-2-lijiang@redhat.com> <20181203150809.GA4794@zn.tnic>
 <779dbae7-f6e2-e9e4-bdd0-0a9e6ec62487@redhat.com>
 <20181205101653.GA6940@dhcp-128-65.nay.redhat.com>
From:   lijiang <lijiang@redhat.com>
Message-ID: <72c311b4-1946-0bcf-54d9-9fcd7f6e630c@redhat.com>
Date:   Wed, 5 Dec 2018 22:21:46 +0800
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在 2018年12月05日 18:16, Dave Young 写道:
>>>> +init_uts_ns
>>>> +===========
>>>> +This is the UTS namespace, which is used to isolate two specific elements
>>>> +of the system that relate to the uname system call. The UTS namespace is
>>>> +named after the data structure used to store information returned by the
>>>> +uname system call.
>>>
>>> Those non-obvious exports should also have a short explanation why
>>> they're part of VMCOREINFO.
>>>
>>>> +
>>>> +node_online_map
>>>> +===============
>>>> +It is a macro definition, actually it is an arrary node_states[N_ONLINE],
>>>> +and it represents the set of online node in a system, one bit position
>>>> +per node number.
>>>
>>> Ditto.
>>>
>>> So yeah, people can find out what those things are but I think it is
>>> more important to state here *why* they're part of VMCOREINFO and how
>>> they're used and why they're exported.
>>>
>>
>> This is a good question.
>>
>> For these two *why*, it should be easy to understand. Because user-space tools
>> need to know basic information, such as the symbol values, field offset, structure
>> size, etc. Otherwise, these tools won't know how to analyze the memory of the crash
>> kernel.
>>
>> For the second question 'how they are used', we can get the answer from user-space
>> tools, such as makedumpfile, crash tools. Therefore, it may not need to explain any
>> more in kernel document. On the other hand, if we must put these contents into kernel
>> document, i have to say, that would be a hard task.
> 
> It should be a good chance to learn how makedumpfile works :),  Maybe it is
> hard to get *all* of them, but it would be good to dig and find the
> thing you can find then explain it.  And leave those *unknown* part as
> FIXME or TODO, people can add description later. 
> 

Thank you, Dave.

It looks like a good idea.


Regards,
Lianbo

> Added Kazu in cc as well..
> > Thanks
> Dave
>