Re: Modprobe as script breaks initramfs kernel?

From: Michael Tokarev
Date: Thu Feb 22 2007 - 15:52:42 EST

Jan Engelhardt wrote:
> On Feb 22 2007 14:30, Michael Tokarev wrote:
>> Deepak Saxena wrote:
>>> We attempted an experiment in cleaning up some modprobe messages during
>>> initramfs bootup when the modules directory is missing by moving modprobe
>>> to modprobe-bin and replacing modprobe with the following simple shell script:
>>> #!/bin/sh
>>> # Clean up bootup when modules are not present
>>> if [ -e "/lib/modules/'uname -r'/modules.dep" ] ; then
>>> /sbin/modprobe-bin $*
> The nitpick guide says: `uname -r` and "$@" instead of $* ;-)

Here, it's possible to workaround the pipefs issue... with another kernel
bugfix. uname -r is available in /proc/sys/kernel/version, but the problem
is that reading almost any file in /proc with shell, which does read by a
single byte, returns only first byte of of the file being read. The bug
has been addressed by Andrew recently, but I don't remember if the fix is
in 2.6.20 or 2.6.19.x yet. I discovered it exactly because of this very
issue - hit pipefs bug and tried to work around it by replacing the above
construct with

read version < /proc/sys/kernel/version
... /lib/modules/$version/modules.dep ...

wich results in $version being set to.. "2" (from "2.6...." :)

But sure, the usage is wrong, albiet ok for some minimal debugging.

>>> BUG: unable to handle kernel NULL pointer dereference at virtual address 00000014
>>> Trace; c0107737 <sys_pipe+17/60>

>> This is the same issue I reported much earlier with /sbin/hotplug being a script
>> in initrfamfs. The problem is because pipefs isn't initialized yet at the time
>> the script gets called, and causes a NULL-pointer deref. Obviously you're using
>> pipe above.
> Btw, has this pipefs issue been adressed (by moving pipefs before initramfs
> stage), or something?

Not as I know of. It has been discussed, but seems to be of low priority.

At least, reading /proc file is fixed... somewhere... :) So it's now possible
to work around it, at least in some places (because sometimes pipe is really
useful anyway and difficult to substitute with something ;)

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