linux-kernel - Re: Kernelmessage to usbstick?

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Message-ID: <496A3567.3090900@rtr.ca>
Date:	Sun, 11 Jan 2009 13:07:35 -0500
From:	Mark Lord <lkml@....ca>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Hans de Bruin <bruinjm@...all.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: Kernelmessage to usbstick?

Oliver Neukum wrote:
> Am Saturday 10 January 2009 23:53:15 schrieb Andi Kleen:
>> Hans de Bruin <bruinjm@...all.nl> writes:
>>
>>> Would it be possible to send kernel messages to an usbstick? On
>>> poweroff my laptop displays a kernel trace and a final message:
>>> poweroff[3114] exited with preempt_count 2
>>> /etc/rc.d/rc.0: line 265: 3114 Segementation fault /sbin/poweroff.
>>> I don't have a serial cable within reach, but plenty of usbsticks.
>> There's a mtdoops.c indeed, but it currently only works on
>> MTD controlled flash devices, not usb sticks.
>>
>> However usb sticks would need the USB subsystem to be running and it's
>> unlikely that will be the case really late in poweroff.  So it might
>> not help.
> 
> USB in turn needs PCI, interrupts and DMA.
..

Dunno about an oops, but I currently use a USB device to
display debug messages from the shutdown procedure,
all the way to kernel_halt().

So long as the Oops doesn't kill too much low level stuff,
it's probably feasible.  Except for the very slow write times
for many USB storage devices.
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