linux-kernel - Re: [PATCH v3 01/21] vmcore: reference e_phoff member explicitly to get position of program header table

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Message-ID: <20130321141202.GF3934@redhat.com>
Date:	Thu, 21 Mar 2013 10:12:02 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	ebiederm@...ssion.com, cpw@....com,
	kumagai-atsushi@....nes.nec.co.jp, lisa.mitchell@...com,
	heiko.carstens@...ibm.com, akpm@...ux-foundation.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	zhangyanfei@...fujitsu.com
Subject: Re: [PATCH v3 01/21] vmcore: reference e_phoff member explicitly to
 get position of program header table

On Thu, Mar 21, 2013 at 11:50:41AM +0900, HATAYAMA Daisuke wrote:
> From: "Eric W. Biederman" <ebiederm@...ssion.com>
> Subject: Re: [PATCH v3 01/21] vmcore: reference e_phoff member explicitly to get position of program header table
> Date: Tue, 19 Mar 2013 14:44:16 -0700
> 
> > HATAYAMA Daisuke <d.hatayama@...fujitsu.com> writes:
> > 
> >> Currently, the code assumes that position of program header table is
> >> next to ELF header. But future change can break the assumption on
> >> kexec-tools and the 1st kernel. To avoid worst case, reference e_phoff
> >> member explicitly to get position of program header table in
> >> file-offset.
> > 
> > In principle this looks good.  However when I read this it looks like
> > you are going a little too far.
> > 
> > You are changing not only the reading of the supplied headers, but
> > you are changing the generation of the new new headers that describe
> > the data provided by /proc/vmcore.
> > 
> > I get lost in following this after you mangle merge_note_headers.
> > 
> > In principle removing silly assumptions seems reasonable, but I think
> > it is completely orthogonal to the task of maping vmcore mmapable.
> > 
> > I think it is fine to claim that the assumptions made here in vmcore are
> > part of the kexec on panic ABI at this point, which would generally make
> > this change unnecessary.
> 
> This was suggested by Vivek. He prefers generic one.
> 
> Vivek, do you agree to this? Or is it better to re-post this and other
> clean-up patches as another one separately to this patch set?

Given the fact that current code has been working, I am fine to just
re-post and take care of mmap() related issues. And we can take care
of cleaning up of some assumptions about PT_NOTE headers later. Trying
to club large cleanup with mmap() patches is making it hard to review.

Thanks
Vivek
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