[systemd-devel] sd-bus object manager question

[David Härdeman]

On Sat, Jun 27, 2015 at 09:22:45AM +0200, David Härdeman wrote:
>On Thu, Jun 25, 2015 at 04:25:29PM +0200, David Herrmann wrote:
>>On Tue, Jun 23, 2015 at 2:41 PM, David Härdeman <david at hardeman.nu> wrote:
>...
>>> Now, a question...how is an object manager supposed to be implemented in
>>> sd-bus?
>>>
>>> I've seen that there's a sd_bus_add_object_manager() function in sd-bus.h,
>>> but how would I notify the object manager when objects are added and
>>> removed?
>>>
>>> Two likely candidates seemed to be:
>>> sd_bus_emit_object_added()
>>> sd_bus_emit_object_removed()
>>>
>>> But calling them did not seem to do the right thing. And there seems to be
>>> zero usage of sd_bus_add_object_manager() in the systemd tree itself (though
>>> plenty of calls to sd_bus_add_node_enumerator() which might be related?).
>>
>>Not sure where the confusion is. Those calls generate the
>>InterfacesAdded/Removed signals that the objectmanager API specifies.
>>They collect the interfaces based on the vtables you registered on a
>>given path. have a look at test-bus-objects.c which uses these
>>interfaces.
>
>I've done some more experimentation and I think I've got a better idea
>of what's going on. Sorry if my first email was a bit confusing.
>
>My problem is that I couldn't get the sd-bus object manager to properly
>notify clients when objects are added or removed.
>
>I'm testing my sd-bus server with a gdbus client. The
>GDBusObjectManagerClient should normally generate signals (gobject
>signals, that is) when objects are added or removed.
>
>Anyway, I tried implementing an object manager server with gdbus as
>well, and when talking to the gdbus server, the client is notified of
>object additions/removals, so I used used busctl to monitor the signals
>that were generated. I think I've found the problem.
>
>Assume there's an object manager at "/org/example/mgr" and that a new
>object is created at "/org/example/mgr/object1".
>
>With sd-bus, I'd call:
>sd_bus_emit_object_added(bus, "/org/example/mgr/object1");
>
>The generated signal would be:
>‣ Type=signal  Endian=l  Flags=1  Version=1  Priority=0 Cookie=11
>  Sender=:1.297  Path=/org/example/mgr/object1
>Interface=org.freedesktop.DBus.ObjectManager  Member=InterfacesAdded
>  UniqueName=:1.297
>  MESSAGE "oa{sa{sv}}" {
>          OBJECT_PATH "/org/example/mgr/object1";
>
>With gdbus, the generated signal is instead:
>The generated signal would be:
>‣ Type=signal  Endian=l  Flags=1  Version=1  Priority=0 Cookie=21
>  Sender=:1.297  Path=/org/example/mgr
>Interface=org.freedesktop.DBus.ObjectManager  Member=InterfacesAdded
>  UniqueName=:1.297
>  MESSAGE "oa{sa{sv}}" {
>          OBJECT_PATH "/org/example/mgr/object1";
>
>Note the difference in the sender path.
>
>The GDBusObjectManagerClient seems to ignore the signal sd-bus generates
>because of the different path.
>
>I think that means that sd_bus_emit_object_added() would need to take
>both the object manager path and the object path as arguments instead of
>a single path?

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