From: "Américo Wang" <xiyou.wangcong@gmail.com>
To: linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary
Date: Mon, 20 Jun 2011 02:42:47 +0000 [thread overview]
Message-ID: <BANLkTi=MeNcOhxU2TYvaC+xwebxcROnjcw@mail.gmail.com> (raw)
In-Reply-To: <201106171155.32062.ptesarik@suse.cz>
On Fri, Jun 17, 2011 at 5:55 PM, Petr Tesarik <ptesarik@suse.cz> wrote:
> Dne Pá 17. června 2011 11:30:32 Ingo Molnar napsal(a):
>> * Petr Tesarik <ptesarik@suse.cz> wrote:
>> > This patch series enhances /dev/mem, so that read and write is
>> > possible at any address. The patchset includes actual
>> > implementation for x86.
>>
>> This series lacks a description of why this is desired.
>
> Hi Ingo,
>
>> My strong opinion is that it's not desired at all: /dev/mem never
>> worked beyond 4G addresses so by today it has become largely obsolete
>> and is on the way out really.
>>
>> I'm aware of these current /dev/mem uses:
>>
>> - Xorg maps below 4G non-RAM addresses and the video BIOS
>>
>> - It used to have some debugging role but these days kexec and kgdb
>> has largely taken over that role - partly due to the 4G limit.
>
> It is still used as a "memory source" by Dave Anderson's crash utility for
> live examination of a running system. Redhat has "overcome" the /dev/mem
> deficiencies by writing an out-of-tree re-implementation of /dev/mem, which
> uses /dev/crash instead. As it is an "unnecessary duplication of an existing
> driver", this method was rejected by the project manager here at SUSE.
>
> The suggested alternative was to enhance (or fix) the existing driver. Without
> this patch series there is no way to access high memory. In conjunction with
> CONFIG_HIGHPTE, it makes the crash utility near to useless on anything with
> high memory, because crash can no longer translate virtual to physical
> addresses.
>
How about /proc/kcore? AFAIK, it can access highmem, but Dave didn't consider
it for some reason.
next prev parent reply other threads:[~2011-06-20 2:42 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-17 8:38 [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses Petr Tesarik
2011-06-17 8:45 ` [PATCH 04/10] ia64: change xlate_dev_mem_ptr's argument to phys_addr_t Petr Tesarik
2011-06-17 8:47 ` [PATCH 08/10] ia64: change valid_phys_addr_range's @addr param " Petr Tesarik
2011-06-17 9:30 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Ingo Molnar
2011-06-17 9:41 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of Russell King - ARM Linux
2011-06-17 9:55 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses Petr Tesarik
2011-06-20 2:42 ` Américo Wang [this message]
2011-06-27 7:46 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of Petr Tesarik
2011-06-19 23:02 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Ryan Mallon
2011-06-19 23:44 ` H. Peter Anvin
2011-06-20 7:41 ` Ingo Molnar
2011-06-20 15:59 ` H. Peter Anvin
2011-06-20 16:40 ` Ingo Molnar
2011-06-20 16:44 ` H. Peter Anvin
2011-06-21 6:56 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of Srivatsa Vaddagiri
2011-06-20 0:42 ` Matthew Wilcox
2011-06-20 0:46 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Ryan Mallon
2011-06-20 0:52 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of Matthew Wilcox
2011-06-20 1:02 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Ryan Mallon
2011-06-20 7:31 ` Ingo Molnar
2011-06-20 8:03 ` Ryan Mallon
2011-06-20 17:10 ` Ray Lee
2011-06-29 9:05 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses Petr Tesarik
2011-07-01 12:58 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Ingo Molnar
2011-07-01 13:43 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses Petr Tesarik
2011-07-01 13:47 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Christoph Hellwig
2011-07-01 14:37 ` Ingo Molnar
2011-07-01 14:41 ` Christoph Hellwig
2011-07-01 14:46 ` Ingo Molnar
2011-07-01 14:54 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses Petr Tesarik
2011-07-01 15:36 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Ingo Molnar
2011-07-01 16:00 ` H. Peter Anvin
2011-07-01 16:13 ` Ingo Molnar
2011-07-01 19:34 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses Petr Tesarik
2011-07-01 19:56 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Ingo Molnar
2011-07-01 20:44 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses Petr Tesarik
2011-07-03 19:46 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary Ingo Molnar
2011-07-05 17:49 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of Matthew Garrett
2011-07-05 17:56 ` [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary H. Peter Anvin
2011-07-05 22:34 ` H. Peter Anvin
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