NMDeviceWifi "scanning" notifier inaccurate

Hi Dan,

I finally got round to investigating this issue:

To summarize, notifications of the "scanning" property of NMDeviceWifi
are not always generated when reading this value would in fact produce
a different value from before.

This property is implemented as a call to
nm_supplicant_interface_get_scanning() which is implemented as "return
TRUE if the supplicant state is scanning, or if the supplicant
asserted the flag saying that scanning is in-progress"

When the supplicant asserts/deasserts the "scanning" flag, we
correctly arrive in supplicant_iface_notify_scanning_cb() which
generates a notification on the property. The bug is that NMDeviceWifi
doesn't watch for relevant changes in the supplicant state to generate
the notification in the other cases when this property can change

The bug I'm seeing is:
1. eth0 is scanning, so the supplicant state is: scanning=1 state=scanning

2. I activate a connection on msh0. real_act_stage1_prepare() in the
mesh device realizes that the companion is scanning so it returns
The driver is listening for changes in the NMDeviceWifi scanning
property so that it can continue the state progression of msh0.

3. supplicant state changes to: scanning=0 state=scanning
The "notify" event is generated on NMDeviceWifi but the scanning
property still reads false so nothing interesting happens.

4. supplicant state changse to: scanning=0 state=disconnected
At this point no notify event is generated, but it should be, because
reading NMDeviceWifi's scanning property will now finally read FALSE.

I'm attaching a patch that fixes the issue. It will generate a few
more notify events than needed (i.e. it will sometimes notify when no
property change happened) but I can't think of a nice way to make this
more accurate. What do you think?

Index: NetworkManager-
--- NetworkManager-
+++ NetworkManager-
@@ -2389,6 +2389,8 @@ supplicant_iface_connection_state_cb_han
+		g_object_notify (G_OBJECT (self), "scanning");
 	finish_supplicant_task (task, FALSE);
 	return FALSE;

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