linux-kernel - Re: [PATCH 1/2 v2] kdump: add the vmcoreinfo documentation

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Date:   Wed, 5 Dec 2018 18:16:53 +0800
From:   Dave Young <dyoung@...hat.com>
To:     lijiang <lijiang@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, tglx@...utronix.de, mingo@...hat.com,
        x86@...nel.org, akpm@...ux-foundation.org, bhe@...hat.com,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        Kazuhito Hagio <k-hagio@...jp.nec.com>
Subject: Re: [PATCH 1/2 v2] kdump: add the vmcoreinfo documentation

> >> +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. 

Added Kazu in cc as well..

Thanks
Dave