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SubjectRe: [PATCH v2] char drivers: Ram oops/panic logger
Il 12/03/2010 23:48, Andrew Morton ha scritto:
> On Wed, 10 Mar 2010 13:15:25 +0100
> Marco Stornelli <marco.stornelli@gmail.com> wrote:
>
>> 2010/3/10 Yuasa Yoichi <yuasa@linux-mips.org>:
>>> 2010/3/10 Marco Stornelli <marco.stornelli@gmail.com>:
>>>> 2010/3/10 Yuasa Yoichi <yuasa@linux-mips.org>:
>> 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?

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?

For my test I used the program devmem2 to dump the log. In general, you
can read the memory via /dev/mem. There's an header plus a timestamp of
the log. The memory is initialized with blank spaces and the size of the
record is fixed at 4k, so if a program/script doesn't find the header at
next 4k, it means there's garbage and it can stop the read operation.

>
> Should the kernel provide the 4k of memory rather than (or in addition
> to) requiring that the system administrator reserve it and tell the
> kernel about it? That'd be a matter of creating a linker section which
> isn't cleared out by the startup code.
>
>

Yes, it can be an option. My first idea was to write a "general" driver,
with an address in input that it can be related to the reserved RAM as
an NVRAM in the system, however it can be a good idea, why not.

Marco


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