linux-kernel - Re: /proc/vmcore mmap() failure issue

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Message-ID: <20131115142617.GC6637@redhat.com>
Date:	Fri, 15 Nov 2013 09:26:17 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	Baoquan He <bhe@...hat.com>,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Atsushi Kumagai <kumagai-atsushi@....nes.nec.co.jp>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Dave Young <dyoung@...hat.com>, WANG Chao <chaowang@...hat.com>
Subject: Re: /proc/vmcore mmap() failure issue

On Fri, Nov 15, 2013 at 06:41:52PM +0900, HATAYAMA Daisuke wrote:

[..]
> >Given the fact that hpa does not like fixing it in kernel. We are left
> >with option of fixing it in following places.
> >
> >- Drop partial pages in kexec-tools
> >- Drop partial pages in makeudmpfile.
> >- Read partial pages using read() interface in makedumpfile
> >- Modify /proc/vmcore to copy partial pages in second kernel's memory.
> >
> >It is not clear to me that partial pages are really useful.  So I want
> >to avoid modifying /proc/vmcore to deal with partial pages and increase
> >complexity.
> >
> >So fixing makedumpfile (either option2 or option 3) seems least risky
> >to me. In fact I would say let us keep it simple and truncate partial
> >pages in makedumpfile to keep it simple. And look at option 3 once we
> >have a strong use case for partial pages.
> >
> >What do you think?
> >
> 
> As you say, it's not clear that partial pages are really useful, but on
> the other hand, it seems to me not clear that they are really useless.
> I think we should get them as long as we have access to them.
> 
> It seems best to me the option 3). Switching between read and mmap would
> be not so complex and also it's by far flexible in makedumpfile than in
> kernel.

Ok, I am fine with option 3. It is more complicated option but safe
option.

Is there any chance that you could look into fixing this. I have no
experience writing code for makedumpfile.

Thanks
Vivek
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