Re: communicating with user login sessions

[David Brownell <david-b@pacbell.net>]

Havoc Pennington wrote:
> 
> How the events get to D-BUS is something I'd defer to kernel hackers
> on - I can't say I have an informed opinion.  Basically I gather
> there's some minimal hook to get the event to a userspace process, and
> that process connects to D-BUS and sends the event.

Yes, /sbin/hotplug is that minimal hook for now; though
nothing prevents faster event delivery schemes, should they
ever really be needed.  (*)

 From what you say, it seems that someone could whip up a
shell script giving us a hotplug-to-DBus gateway, by using
that "dbus-send" program (not in dbus-0.9?) to deliver a
hotplug event like:

       Header:
           name "org.kernel.hotplug.Kernel.Event"
           srvc ... goes to how many listeners? ...
           sndr ... whatever kernel authenticates itself as ...

       Arguments
           uint64 - timestamp
           string - argv [0]
           string - argv [1]
           ...
           nil
           string - envp [0]
           string - envp [1]
           ...
           nil

I'd really like to see someone send by such a script, perhaps
an "/etc/hotplug/input.agent" to forward input hotplug events
so that an X11-ish component can at least monitor keyboards,
wheels, drum kits, and such as they appear/disappear.

Eventually of course, that component should make many of those
devices available as X11 input devices... :)

- Dave

(*) I can imagine some kernel switch controlling how the hotplug
     event gets formatted and delivered.  One option would be
     to spawn a process, as we've done so far.  Another would be
     to queue the events so some process could read them out in
     the appropriate format. I'd not be surprised to find people
     needing that second option by the time 2.7 starts.




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