linux-kernel - Re: [PATCH 0/3 -mm] kexec jump -v8

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Message-ID: <20071227181218.GA15084@redhat.com>
Date:	Thu, 27 Dec 2007 13:12:18 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3 -mm] kexec jump -v8

On Thu, Dec 27, 2007 at 10:33:13AM +0800, Huang, Ying wrote:
> On Wed, 2007-12-26 at 20:57 -0500, Vivek Goyal wrote:
> [...]
> > > 9. Now, you are in the original kernel again. You can read/write the
> > >    memory image of kexeced kernel via /proc/kimgcore.
> > > 
> > 
> > Why do we need two interfaces, /proc/vmcore and /proc/kimgcore? Can't
> > we have just one say /proc/vmcore. Irrespective of what kernel you are
> > in /proc/vmcore gives you the access to the memory of kernel which was
> > previously booted.
> 
> In theory we can kexec another kernel even in a kexeced kernel, that is,
> in kernel A kexec kernel B, and in kernel B kexec another kernel C. In
> this situation, both /proc/vmcore and /proc/kimgcore has valid contents.
> So I think, it may be better to keep two interfaces.
> 

In those situations I think only one interface is better. For example, 
above will be broken if somebody kexec 4 kernels.

A-->B--->C--->D

I think better option might be if it is stack like situation. A kernel
shows you only the previous kernel's memory contents through /proc/vmcore
interface. So If I am in kernel D, I see only kernel C's memory image.
To see kernel B's memory image, one shall have to go back to kernel C.

Thanks
Vivek
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