[systemd-devel] Still confused with socket activation

[Reindl Harald]

Am 03.02.21 um 10:43 schrieb Benjamin Berg:
> On Wed, 2021-02-03 at 08:00 +0100, Reindl Harald wrote:
>>
>>
>> Am 02.02.21 um 22:25 schrieb Benjamin Berg:
>>> On Tue, 2021-02-02 at 22:50 +0300, Andrei Borzenkov wrote:
>>>> 02.02.2021 17:59, Lennart Poettering пишет:
>>>>>
>>>>> Note that Requires= in almost all cases should be combined with
>>>>> an
>>>>> order dep of After= onto the same unit.
>>>>
>>>> Years ago I asked for example when Requires makes sense without
>>>> After.
>>>> Care to show it? I assume you must have use case if you say "in
>>>> almost all".
>>>
>>> In the GNOME systemd units there are a few places where a Requires=
>>> is
>>> combined with Before=
>>
>> sounds like complete nonsense
>>
>> you can not require something at your own to be there but on the other
>> hand start before it - at least by common sense
> 
> The units are indeed non-trivial. I have put in a lot of effort to find
> a solution that both works and is robust in various failure modes. It
> may well be that there is a better approach with similar properties.
> But, session login and logout(!) is not quite as trivial as one could
> hope for unfortunately (backward compatibility and workarounds add some
> complexities).
> 
> So, I would love to be educated on how to simplify all this while still
> catching the various corner cases. But in order to convince me, you'll
> need to make a more concrete suggestion and explain its properties

seriously - explain what you expect to happen in case of

Requires=a.service
Before=a.service

except some warning that it's nonsense

you need a.service but want to be started before a.service sounds like 
wash me but don't make me wet