[lug] logging missing 2.6 kernel modules

Zan Lynx zlynx at acm.org
Mon Jun 13 10:50:03 MDT 2005

On Sun, 2005-06-12 at 23:25 -0600, D. Stimits wrote:
> Lee Woodworth wrote:
> > In reviewing the hotplug and udev stuff, I was reminded of
> > some things I have seen on the web that apply:
> > 
> >    Kernel version 2.6 will not automaticlly load device drivers
> >    when a related device node is accessed. The major reason
> >    being that there is interest in having device major/minor
> >    become dynamially allocated. For example the device mapper
> >    (dm_mod) already uses a dynamic minor number for
> >    /dev/mapper/control.
> > You may be interested in this excerpt from the udev FAQ:
> > 
> >    Q: But udev will not automatically load a driver if a /dev node is opened
> >       when it is not present like devfs will do.
> >    A: If you really require this functionality, then use devfs.  It is still
> >       present in the kernel.
> As far as I know I'm not using udev. For the old devfs it's easy to 
> check (not using it), I'm coming up blank trying to figure what kernel 
> config is for udev.

There is no kernel configuration for udev.  The "u" in udev is for
user-space.  The only bit that is done in the kernel is hotplug
notification.  udev picks up static devices through boot scripts, called
hotplug or coldplug, depending on the distro.  The boot scripts scan for
hardware and simulate hotplug calls for the hardware.

For Gentoo, they have a coldplug script but recommend loading the
modules statically if you know what you've got plugged in, since it is

> >    Q: But wait, I really want udev to automatically load drivers when they
> >       are not present but the device node is opened.  It's the only reason I
> >       like using devfs.  Please make udev do this.
> >    A: No.  udev is for managing /dev, not loading kernel drivers.
> I'm actually hoping for some *other* mechanism to do this, not udev.

If you set the option in the kernel configuration, it will still call
out to modprobe to load things like SCSI or network drivers.  If that
isn't working, it could be that modprobe is disabled by your distro
writing an empty line into /proc/sys/kernel/modprobe.  Make sure that's
set to /sbin/modprobe.

Zan Lynx <zlynx at acm.org>
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