linux-kernel - Re: [PATCH v2] char drivers: Ram oops/panic logger

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Message-ID: <10f740e81003130650j76698721g75186091253bb99c@mail.gmail.com>
Date:	Sat, 13 Mar 2010 15:50:48 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Marco Stornelli <marco.stornelli@...il.com>,
	Yuasa Yoichi <yuasa@...ux-mips.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Embedded <linux-embedded@...r.kernel.org>
Subject: Re: [PATCH v2] char drivers: Ram oops/panic logger

On Fri, Mar 12, 2010 at 23:48, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Wed, 10 Mar 2010 13:15:25 +0100
> Marco Stornelli <marco.stornelli@...il.com> wrote:
>
>> 2010/3/10 Yuasa Yoichi <yuasa@...ux-mips.org>:
>> > 2010/3/10 Marco Stornelli <marco.stornelli@...il.com>:
>> >> 2010/3/10 Yuasa Yoichi <yuasa@...ux-mips.org>:
>> >>> Hi,
>> >>>
>> >>> 2010/3/10 Marco Stornelli <marco.stornelli@...il.com>:
>> >>>> Ramoops, like mtdoops, can log oops/panic information but in RAM.
>> >>>
>> >>> What is different from mtdoops + mtd-ram?
>> >>>
>> >>> Yoichi
>> >>>
>> >>
>> >> It can be used in a very easy way with persistent RAM for systems
>> >> without flash support. For this systems, with this driver, it's no
>> >> more needed add to the kernel the mtd subsystem with advantage in
>> >> footprint as I said in the description.
>> >
>> > right.
>> > But,
>> >
>> >> In addition, you can save
>> >> flash space and store this information only in RAM. I think it's very
>> >> useful for embedded systems.
>> >
>> > CONFIG_MTD_RAM uses only RAM.
>> > I think there's no big difference about this point.
>> >
>>
>> I meant with the "classic" use of mtdoops, therefore with a flash
>> partition without use MTD_RAM. Using MTD_RAM, it's more or less the
>> same thing, with the exception of "where" you want deploy the log. For
>> example: if in your system you have got a nvram you can use it without
>> problem, you need to specify the address of the nvram to the module.
>> Very simple. I  think it's a small driver but very useful, feedback
>> from other embedded guys are welcome.
>
> Seems sensible to me.  If you have a machine whose memory is persistent
> across reboots then you reserve an arbitrary 4k hunk of memory for
> collecting oops traces, yes?
>
> What tools are used for displaying that memory on the next boot?  How
> do those tools distinguish between "valid oops trace" and "garbage
> because it was just powered on"?  A magic signature?

On Amiga, `debug=mem' enables something like that, cfr. git grep dmesg
arch/m68k.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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