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

[David Herrmann]

Hey

On Tue, Apr 25, 2017 at 10:05 AM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Tue, 25.04.17 09:54, David Herrmann (dh.herrmann at gmail.com) wrote:
>
>> >> 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?
>>
>> No, it does not. sd-bus was inconsistent. See, there are 3 things
>> involved in the Object-Manager:
>>
>> Signal: InterfacesAdded
>> Signal: InterfacesRemoved
>> Call: GetManagedObjects
>>
>> The first two signals are used to add and remove objects (and their
>> respective interfaces) at runtime. The GetManagedObjects() call is
>> used to bootstrap, that is, to get the initial set of objects (and
>> their respective interfaces) when starting your application.
>>
>> So far, sd-bus reported the builtin interfaces correctly via the
>> signals, but did not return that information in the
>> GetManagedObjects() call. My patch fixed this omission.
>> The effect of this is that objects added/removed at runtime work fine,
>> but if an object was there already when your application starts, then
>> it will never be removed, since gdbus will see an interface-count
>> mismatch (as you observed above).
>>
>> Hence, the patch I provided fixes how sd-bus provides this
>> information. It does *not* change any policy.
>>
>> I think the 2 underlying problems you saw are bugs in both gdbus and
>> sd-bus. The one in sd-bus I tried to fix above, the one in gdbus is
>> only about counting interfaces and properly detecting negative
>> interface-counts. The gdbus bug is non-severe, though, since it
>> originates in a buggy remote client. So there is no hard reason to
>> change gdbus there.
>
> Could you please send the sd-bus side fix as PR?

Now pending as #5799.

Thanks
David