linux-kernel - Re: does /proc/sys/kernel/modprobe actually do anything?

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Date:	Thu, 29 Nov 2007 18:14:02 +0100
From:	"Kay Sievers" <kay.sievers@...y.org>
To:	"Robert P. J. Day" <rpjday@...shcourse.ca>
Cc:	"Alexey Dobriyan" <adobriyan@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: does /proc/sys/kernel/modprobe actually do anything?

On Nov 29, 2007 1:58 PM, Robert P. J. Day <rpjday@...shcourse.ca> wrote:
> On Thu, 29 Nov 2007, Alexey Dobriyan wrote:
>
> > On 11/29/07, Robert P. J. Day <rpjday@...shcourse.ca> wrote:
> > > echo '#! /bin/sh' > /tmp/modprobe
> > > echo 'echo "$@" >> /tmp/modprobe.log' >> /tmp/modprobe
> > > echo 'exec /sbin/modprobe "$@"' >> /tmp/modprobe
> > > chmod a+x /tmp/modprobe
> > > echo /tmp/modprobe > /proc/sys/kernel/modprobe
> > >
> > >   i've tried that and i don't see that it does anything whatsoever.  i
> > > ran modprobe under "strace" and it doesn't appear to make any effort
> > > to check /proc/sys/kernel/modprobe.
> >
> > Kernel, not modprobe, checks /proc/sys/kernel/modprobe .
>
> actually, ignore that earlier query of mine, i've found the relevant
> code under kernel/ in sysctl.c and sysctl_check.c and kmod.c.  but
> it's still not clear why what is described in
> Documentation/debugging-modules.txt (and shown above) doesn't work, so
> i'm still open to suggestions.  thanks.

Kernel code can request a module to be loaded by calling request_module().
The /proc/sys/kernel/modprobe value is the path to the binary which the kernel
executes when this function is called. It is used by some modules, or if you
open an existing device node which has no actual driver loaded.

Most modules are loaded by device id's (modalias) of  a device.
The module is loaded by pure userspace tools and not by the kernel and
therefore /proc/sys/kernel/modprobe is not involved at all in most module
loading.

The text in Documentation/debugging-modules.txt is purely about kernel
module loading requests, and not helpful for the common module loading
case.

Kay
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