Re: Talking to NM 0.7 with dbus vs. libnm_glib

[Dan Williams <dcbw redhat com>]

On Wed, 2009-05-06 at 22:42 +0200, Christian Huff wrote:
> Hi,
> 
> I am currently working at the libpurple/pidgin NetworkManager
> integration code to improve to user experience with roaming with
> multiple devices. Currently, libpurple only reacts to the global
> StateChange signal, which does not change if one device goes offline or
> online and there is another active device. In effect, this often results
> in the inability to send or receive messages - the apps stalls until a
> timeout occurs.
> 
> libpurple gets the current global NM state through Dbus, so, being kinda
> new to glib programming, I tried to get NM's devices, connect to device
> StateChanged, DeviceAdded and DeviceRemoved signals using
> dbus_g_proxy_connect_signal. Doing so, I found I needed to register
> custom marshallers as NetworkManager.h didn't provide them (this was
> with 0.7.0, I haven't checked 0.7.1 yet). Also, I had to store a proxy
> for each device, effectively producing some overly complicated code that
> wouldn't make it into libpurple...

libnm-glib makes this easy for you, as it will proxy these signals into
GObject signals.  You shouldn't really need to touch dbus-glib at all
here.  Using libnm-glib, you could have created a new NMClient object,
then queried that object for the list of devices, or attached to the
'device-added' / 'device-removed' signals or 'state' properties.  I can
explain more if you like.

But the approach you took was wrong.  Not a problem though, given you
hadn't done this before :)

> So I read that libnm_glib was rewritten with 0.7, and rewrote my patch
> using it. The code turned out much cleaner, yet I found some problems
> that I want to share with you. One of the goals I had set myself was to
> minimize the number of unnecessary reconnects. A scheme to do so would
> be to track the devices that are active at a connect action, and
> reconnect only if such a "critical" device goes down. Another would be
> to see if the device currently going down is part of an Active
> Connection (NMActiveConnection) that NM reports as being the/a default
> connection for DNS and routes.

Yeah, I'd expect that whenever the 'default' property on an active
connection changes, that's when you'd want to see if you should
reconnect.

> While the former scheme was not perfect, the latter wasn't reliable,
> either. I found nm_active_connection_get_default() to often return true
> for multiple active connections, and sometimes the value from before and
> sometimes the predicted value from after the device StateChanged event.
> That kind of synchronisation problems currently prevent me from
> implementing that scheme.

That behavior seems wrong.  The NM code should ensure that only one
active connection object has the default property at the same time, but
there may be some latency issues in libnm-glib's proxying of properties.
Or, you may have been checking things at the wrong time.  Can you post
some code, or ideally a distilled testcase?

If libnm-glib is reporting two NMActiveConnection objects having
default=True at the same time, that's something that should get
identified and fixed.

> Also, I tried to entirely replace the dbus functionality, but
> libnm_glib_get_network_state() does not return values equivalent to the
> StateChanged signal, and I didn't find the signal in the libnm_glib docs.

No, it doesn't.  libnm_glib_get_network_state() is the "old" interface
from NM 0.6 that was preserved for minimal compatibility.  You'd want to
create a new NMClient object and attach signals to it:

static void
state_changed (NMClient *client,
               GParamSpec *pspec,
               gpointer user_data)
{
    NMState state;

    state = nm_client_get_state (client);
    <do something here>
}

static void
active_connections_changed (NMClient *client,
                            GParamSpec *pspec,
                            gpointer user_data)
{
    const GPtrArray *acs = nm_client_get_active_connections (client);
    int i;

    for (i = 0; i < acs->len; i++) {
        NMActiveConnection *ac = g_ptr_array_index (acs, i);

        if (nm_active_connection_get_default (ac))
            <its default>
    }
}
                           

int main (...)
{
    NMClient *client;

    client = nm_client_new ();

    /* Monitor state */
    g_signal_connect (client, "notify::state",
                      G_CALLBACK (state_changed), my_data);

    g_signal_connect (client, "notify::active-connections",
                      G_CALLBACK (active_connections_changed), my_data);

    g_main_loop_run (loop);

    g_object_unref (client);
}

Dan

> The current version of my patch reconnects any time a device enters or
> leaves the NM_DEVICE_STATE_ACTIVATED state, and can be found at:
> 
> http://developer.pidgin.im/ticket/8694
> 
> thanks for your feedback,
> 
> Christian Huff (Pedric)
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