[systemd-devel] sd-bus: ObjectManager difference with gdbus

[David Härdeman]

April 21, 2017 1:22 PM, "David Herrmann" <dh.herrmann at gmail.com> wrote:
> On Fri, Apr 21, 2017 at 11:50 AM, David Härdeman <david at hardeman.nu> wrote:
>> On Thu, Apr 20, 2017 at 02:19:22PM +0200, David Herrmann wrote:
>>> On Thu, Apr 20, 2017 at 12:06 PM, David Härdeman <david at hardeman.nu> wrote:
>> I'm implementing a server which creates an ObjectManager using the
>> sd-bus API and there seems to be some differences between how gdbus and
>> sd-bus implements the API.
>> 
>> I implemented a simple ObjectManager at /org/gnome/TestManager which
>> exports objects /org/gnome/TestManager/fooX with interface
>> org.gnome.TestManager.Device.
>> 
>> Under sd-bus, if an object is removed, the following signal is
>> generated:
>> 
>> signal time=1492642227.714223 sender=:1.104 -> destination=(null destination)
>> serial=90 path=/org/gnome/TestManager;
>> interface=org.freedesktop.DBus.ObjectManager;
>> member=InterfacesRemoved
>> object path "/org/gnome/TestManager/foo0"
>> array [
>> string "org.freedesktop.DBus.Peer"
>> string "org.freedesktop.DBus.Introspectable"
>> string "org.freedesktop.DBus.Properties"
>> string "org.freedesktop.DBus.ObjectManager"
>> string "org.gnome.TestManager.Device"
>> ]
>> 
>> If I implement the same simple server in gdbus, the signal is instead:
>> 
>> signal time=1492642227.714223 sender=:1.104 -> destination=(null destination)
>> serial=90 path=/org/gnome/TestManager;
>> interface=org.freedesktop.DBus.ObjectManager;
>> member=InterfacesRemoved
>> object path "/org/gnome/TestManager/foo0"
>> array [
>> string "org.gnome.TestManager.Device"
>> ]
>> 
>> The corresponding signals are also generated when an object is added.
....
>>> Does the appended patch fix your issue?
>>> (line-breaks might be screwed, sorry)
>> 
>> Haven't tried it yet, but just from reading the patch...it seems to do
>> the opposite of what I'd expect? I.e. add *more* interfaces?
> 
> This change makes sure all objects have the built-in interfaces
> reported at all times. The GetManagedObjects() call didn't report them
> so far.

Quite the contrary? If you look at the output from dbus-monitor above, you'll see that it is sd-bus that already *does* report all interfaces while gdbus doesnt?
 
> Note that we really better report all interfaces an object supports. I
> don't know why glib does not do this, but I think it should.

Maybe, I'm no dbus expert. And there does seem to be a bug in gdbus as well since the additional interfaces manage to confuse it. Anyway, it seems that either sd-bus should adapt the gdbus style or vice versa...maybe you could talk directly to the gdbus people?

Regards,
David