Re: Looking for a clue in how udev, hal, hotplug and dbus work together

[Kay Sievers <kay.sievers@vrfy.org>]

On Tue, Sep 13, 2005 at 12:50:24AM -0400, Jim McQuillan wrote:
> I'm trying to get a grasp on how udev, hal, hotplug and dbus play
> together in detecting devices.
> 
> I'm doing this for LTSP (Linux Terminal Server Project).  This is
> Thin-clients in Linux.  We currently have the ability to plug a usb
> device in, such as a mini-cruizer USB memory stick.  When the device is
> inserted, we have a hotplug script written in perl, that gets the event
> from the kernel, figures out what kind of device it is, loads the
> appropriate kernel modules, mounts the filesystem on the device, and
> then signals the server that a new device is available.  This is all
> under a 2.4.26 kernel.
> 
> Now, I'm moving up to a 2.6.13 kernel, and I'd like to do things the
> "right way".  That is, I'm dropping devfs, and using udev.  I'm thinking
> that to use udev, then I also should be using hal and dbus.  But so far,
> i've not been able to wrap my head around how it all works together.
> 
> from what I've read, it seems that I should be setting
> /proc/sys/kernel/hotplug to "", and that "netlink" is now used for the
> kernel to send messages to udev.  Then, udev sends messages to hald.

udevd listens to kernel uevents over netlink and the event gets matched
against the udev rules, a node created if needed and all postprocessing
hooks (RUN=) in matching udev rules are executed.

/proc/sys/kernel/hotplug should be disabled, but the "input" layer lacks
sysfs support so you need /sbin/udevsend here until that is fixed.

> So, my question is, when a new USB device is plugged in, take the
> 'mini-cruizer' memory stick for example, at what point is the kernel
> module loaded?  Does 'hald' handle that?  or do I still need "hotplug"
> scripts.

The kernel offers a modalias file in sysfs that signifies that a driver
needs to be loaded. You can do this with a simple generic udev rule or
any other facility. Just running modprobe with the content of the
modlias file should be able to replace almost all old hotplug stuff.

> Once the mini-cruizer is detected, where to I put my hooks in, to signal
> the server that a new device is available?

What kind of server?

Kay


-------------------------------------------------------
SF.Net email is Sponsored by the Better Software Conference & EXPO
September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA
Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf
_______________________________________________
Linux-hotplug-devel mailing list  http://linux-hotplug.sourceforge.net
Linux-hotplug-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-hotplug-devel