linux-kernel - Re: kdump: Trouble reading /dev/oldmem from capture kernel

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Date:	Tue, 9 Aug 2011 10:41:41 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Seemanta Dutta <seemanta@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: kdump: Trouble reading /dev/oldmem from capture kernel

On Fri, Aug 05, 2011 at 02:01:03PM -0700, Seemanta Dutta wrote:
> 
> 2. Dump capture kernel provides two interfaces to access 'old' kernel
> memory (as per kdump dpcumentation): /dev/oldmem and /proc/vmcore. The
> latter works perfectly. But I am more interested in the raw memory, rather
> than the core file.

Is there some specific reason to use /dev/oldmem instead? At least I've
never needed that interface. crash utility works pretty well with
/dev/vmcore.

> My expectation in this scenario was that I would be able to access entire
> physical RAM using the /dev/oldmem device. But turns out, I can't.
> 
> I would be grateful if anyone pointed out if I was doing something wrong
> or missing something.
> 
> This is happening over ARM. Could that have to do something with this ?
> Not sure if the ARM integration of KDUMP/KEXEC has something to do with
> it.

I haven't tried lately but it looks like ARM is missing setting of
'saved_max_pfn' which could explain why it works that way.
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