Re: udev and dbus

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

On Wed, 2004-03-10 at 17:31, David Zeuthen wrote:
> Hi Greg and Kay,
> 
> As far as I can tell there are still issues with the dbus support in
> udev due to the fact that udev needs to be available in early boot -
> this issue have been raised a few times with little or response. 
> 
> I'm willing to make a patch to fix it (unless someone beats me to it),
> but before I go ahead I'd like some input on how we want it to look
> like. I can see at least the following three scenarios:
> 
>  1. Remove dbus support from udev and make udev call /sbin/hotplug with
>     a single positional parameter, 'udev', and the environment variables
>     DEVPATH pointing to the appropriate directory in sysfs, ACTION
>     assuming 'add' respectively 'remove' and DEVICE_FILE pointing to
>     the created / removed special device file.

How will you know what file is created?


>     This way, applications, like HAL, interested in the event can simply
>     install a small program in /etc/hotplug.d/[udev,default] to do
>     whatever they want with the event, like sending it to a daemon
>     possibly through what may be the IPC-flavour of the month :-)
> 
>     (yes, this might be abusing the hotplug multiplexor)
> 
>  2. Move dbus support from udev to udevd, make sure udevd never
>     exits, and let udevd own the org.kernel.udev service. I guess
>     this would imply building two udevd binaries; one with
>     dbus support and one without (for early boot) and make the small
>     one load the big one upon receiving SIGUSR1. I think Marco
>     d'Itri came up with this approach.
> 
>     I'm not too familiar with udevd, but I seem to recall that it
>     spawns udev copies to do the work so it may require more tweaking
>     to do this.

Sounds fragile, we multiplex with datagrams and fork in the background
to get the SIGCHLDS later.
I don't think you can send anything like a dbus-message without blocking
the whole thing to dead.


>     However, using this approach, we can also offer queries on the
>     udev database using dbus instead of using udevinfo. That would
>     be nice.
> 
>  3. Remove dbus support and if applications are interested in sending
>     out events using IPC like dbus, they just install a udev callout.
> 
>     I'm not sure this is easy today as all the callout rules are in
>     a single file instead of a directory with rule files. I may be
>     wrong on this though.

Sure, you can specify a whole directory in udev.conf (man udev).


Hmm, don't know what's the best...

thanks,
Kay



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