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Date: Fri, 1 Jul 2011 09:47:05 -0400
From: Christoph Hellwig <hch@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Petr Tesarik <ptesarik@suse.cz>, Andrew Morton <akpm@linux-foundation.org>,
        Fenghua Yu <fenghua.yu@intel.com>, "H. Peter Anvin" <hpa@zytor.com>,
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        Dave Jones <davej@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary
 physical addresses
Message-ID: <20110701134705.GA6175@infradead.org>
References: <201106171038.25988.ptesarik@suse.cz>
 <20110617093032.GA19235@elte.hu>
 <201106291106.00070.ptesarik@suse.cz>
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On Fri, Jul 01, 2011 at 02:58:02PM +0200, Ingo Molnar wrote:
> So what was not mentioned in your series, what is *your* motivation 
> and your usecase? Enabling closed-source userspace drivers? Enabling 
> the crash utility?

He stated it pretty clearly in the thread, it's the crash utility.

> 
> If the former then shame on you, if the latter then how do you 
> explain that distros appear to disable the RAM aspect of /dev/mem:
> 
>  $ grep DEVMEM $(rpm -ql kernel-2.6.38-0.rc7.git2.3.fc16.x86_64 | grep config-2.6 )
>  CONFIG_STRICT_DEVMEM=y
> 
> So the crash utility use-case does not work on unpatched, default 
> kernels, right?

Not if you have highmem.  That's why Redhat or Fedora to quote your
example patch in the /dev/crash driver, which totally defeats the
CONFIG_STRICT_DEVMEM setting.  But apparently it's good enough that no
one either noticed or at least doesn't care.