Re: Do I want to use udev?

[Greg KH <greg@kroah.com>]

On Wed, Jan 04, 2006 at 03:47:06PM -0500, Brian Sammon wrote:
> I'm trying to figure out if I should be using udev, and if so, how.
> I'm upgrading to a recent 2.6 kernel, and various documentation says that udev 
> is required, but I'm not sure.
> 
> I'm not interested in having a dynamic /dev filesystem (for the moment); a 
> static /dev filesystem has served me just fine up to this point, and I think 
> it will continue to work for a little while longer.
> 
> So that leaves me with the other hotplug-related functionality, automatic 
> driver loading.  I can't figure out if, or how, udev does that.

The single rule:
	ENV{MODALIAS}="?*",    RUN+="/sbin/modprobe $env{MODALIAS}"
will cause udev do that.

> In particular, 99% of the hotplugging I do is USB devices, and I can't
> find any file in my (Debian) udev package that configures which USB
> drivers get loaded for which USB devices.

That's the "magic" of the kernel driver providing a
MODULE_DEVICE_TABLE() logic with the modprobe program matching up module
aliases.  See my very old OLS 2001 paper on the basic ideas behind the
whole thing (but it's simpler now, as modprobe does the matching for us,
we don't have to scan the alias tables anymore by hand.)

> This leads me to wonder-- can I disable/uninstall udev altogether, or just 
> disable the dynamic /dev filesystem and still have automatic USB driver 
> loading?

You can, if you only use the one rule above :)

But if that's all that you want to have happen, stick with the old
hotplug package, it still works just fine.  Why would you want to use
udev if you don't care about persistant names and other good stuff it
provides?

> If part/all of my problem is debian specific, I'd still appreciate general 
> information, such as how it should be done, or information about how this 
> works on your system.

I suggest you ask debian udev specific questions on a debian specific
mailing list, you might have better luck that way :)

Hope this helps,

greg k-h


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