How does dbus-daemon handle multiple services with same Name?

[Armin K.]

On 06/21/2015 09:11 PM, Michael Biebl wrote:
> 2015-06-21 20:58 GMT+02:00 Armin K. <krejzi at email.com>:
>> On 06/21/2015 08:42 PM, Lennart Poettering wrote:
>>> On Sun, 21.06.15 13:02, Armin K. (krejzi at email.com) wrote:
>>>
>>>> Hi,
>>>>
>>>> While trying kdbus with systemd, I have ran across a problem.
>>>> Apparently it doesn't yet properly handle multiple D-Bus services
>>>> with same name.
>>>>
>>>> I'm interested in how does D-Bus daemon handle this? Which one
>>>> gets loaded and how it decides which one to load?
>>>>
>>>> An example:
>>>>
>>>> I have two services with Name=org.freedesktop.FileManager1
>>>>
>>>> One is GNOME's Nautilus, other is MATE's Caja File Manager.
>>>> Which one would get loaded and why?
>>>
>>> Only one service can own a name at a time. If one already owns a name,
>>> and another one tries to take possession of it as well, then one of
>>> three things can happen:
>>>
>>>       a) the request to own the name is queued, and dbus-daemon passes
>>>       it on automatically and atomically as soon as the old owner
>>>       voluntarily gives it up.
>>>
>>>       b) the operation to request the name will simply fail (this mode
>>>       of operation you get by passing DBUS_NAME_FLAG_DO_NOT_QUEUE when
>>>       acquiring the name)
>>>
>>>       c) the name will be taken away forcible from the old owner (only
>>>       if the new owner indicated DBUS_NAME_FLAG_REPLACE_EXISTING, and
>>>       the old one DBUS_NAME_FLAG_ALLOW_REPLACEMENT).
>>>
>>> Either way, and no times there are two owners of a name at the same
>>> time, neither in kdbus, nor in dbus-daemon.
>>>
>>> Lennart
>>>
>>
>> I'm asking specifically because current dbus-daemon seems to
>> kinda handle it, but kdbus will error out when it tries to
>> create a symlink for bus-proxyd. I was asked on systemd
>> bug tracker how dbus handles this, that's why I asked here.
> 
> What you are referring to is having files in
> /usr/share/dbus-1/{system}-services/
> which provide the same "Name".
> It's not enforced, that the Name in the .service file is named after
> the D-Bus name.
> 
> So you can have
>  foo.service with Name=org.fdo.baz
> and
>  bar.service with Name=org.fdo.baz
> 
> I think your question is, assuming that neither foo or bar is running,
> and there is an incoming request for org.fdo.baz, which one of the two
> is started?
> 

Yes, that was the question.

The answer to that is probably a solution to this:

https://github.com/systemd/systemd/issues/312

-- 
Note: My last name is not Krejzi.



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