Re: signal for interface up/down

[Dan Williams <dcbw redhat com>]

On Fri, 2016-06-24 at 20:42 +0200, Michael Hirmke wrote:
> Hi Thomas,
>
> > On Fri, 2016-06-24 at 11:56 +0200, Michael Hirmke wrote:
> > > Hi *,
> > >
> > > I'm about to write a script, which should do some actions in a
> > > user
> > > context, whenever an interface is getting active or inactive.
> > > I tried to implement this via the NetworkManager dbus interface
> > > and
> > > the
> > > signals "DeviceNowActive" and "DeviceNoLongerActive".
> > > As it seems, the documentation mentioning these signals is
> > > outdated,
> > > because they don't exist any more. Otherwise I'm doing somtehing
> > > completely wrong.
> > >
> > > Can anyone sched some light on this, please?
> > > Do these signals still exist? If so, is there an example on how
> > > to
> > > use
> > > them? At least I found them mentioned in one of the nm libraries.
> > > If theses signals indeed don't exist any more, how is the
> > > preferred
> > > solution for my problem?
> > >
> > > Thx a lot!
> > >
> > > Bye.
> > > Michael.
>
> > Hi Michael,
>
> > I think you should listen for the device's "State". Also, as a
> > device
> > becomes active, it gets a "ActiveConnection".
> Yes, but what I need is to listen for every connection/device
> becoming
> active or inactive. So I would have to find out, what devices are
> present, then listen to the appropriate signals for *each* of them?

Correct.  But in reality you can just watch for all signals coming out
of NetworkManager.  You'd match on the signal (member) name
"StateChanged", and look for object paths starting with
"/org/freedesktop/NetworkManager/Devices/" and an interface of
"org.freedesktop.NetworkManager.Device".

The Device.StateChanged signal arguments are documented in the NM D-Bus 
API; they are new-state (uint), old-state (uint), and reason (uint).

So once you know you've got a device state change signal, you can read
the new-state argument and you'll know when the device is activated or
deactivated.

This all makes it seem more complicated than it is.  In reality you're
just listening for NetworkManager messages of type SIGNAL, checking a
couple standard message attributes (interface, object path, and member
name), and then reading one uint from the message data.

Dan