Re: udev and dbus

[David Zeuthen <david@fubar.dk>]

On Thu, 2004-03-11 at 15:30, Kay Sievers wrote:
> Sorry, but are you guys getting completely crazy? :)
> 
> Why you want a stacked hotplug.d/udev.d forking hell or a "serializer"
> for the dbus daemon? This is simply unmaintainable and _nobody_ will
> understand this. 

What's so difficult with understanding that udev calls a series of
programs in /etc/udev.d when it add/remove device nodes?

> We have enough problems to teach the /sbin/hotplug and
> udev/udevsend/udevd logic.
> 
> We can rip dbus out and make a external dbus caller, yes that's fine.
> But dbus should use the /sbin/hotplug multiplexer. Just get the needed
> information with udevinfo and then fire up the dbus-client.

This I would recommend against - not every hotplug event makes udev
create/remove a device node; networking devices are one example. 

Oh, and wouldn't there be a potential race with udev, so you'd need to
poll with udevinfo until you get the device file from udevinfo?

> We can also keep udev's dbus-send as it is and just make it switchable.
> If dbus is finally running, you can simply switch it on. But yes,
> ripping it out seems cleaner.
> 

As someone mentioned in another mail, you will still have the potential
problem of the libdbus.so being on /usr which could be a separate
partition from / and, blam, udev can't run to create the device node for
the disk that /usr is on. 

Hence I would argue that it's desirable to keep the code sending the
dbus event in a binary separate from udev. Do you agree?

> So, please please remember the goal of udev :)
> 

I think the proposal is really simple:

 1. Rip out dbus-sender from udev
 2. Make udev call all executables in /etc/udev.d
 3. *optionally* provide a udevdbus program and place it in /etc/udev.d

and I argue this will udev simpler and not depend on dbus at all, while
still maintaining the dbus functionality. Oh, and solving the problem
with 'dbus support is disabled because of...'.

(For the udevdbus program, we could place this in /usr/libexec and
symlink it to /etc/udev.d - udev can then, upon traversing /etc/udev.d,
check if the link is stale or not)

People can even use whatever IPC they may like to use the information
from udev, write custom shell scripts or whatever.

Friendly,
David




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