udev and dbus

[David Zeuthen <david@fubar.dk>]

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.

    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.

    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.

Of course, there might be other ways of acheiving sending out events
through e.g. dbus, but I can't think of any.

Let me know what you think - I'd really like to resolve this issue.

Take care,
David 


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