Registration of TAG+="systemd" udev rules?

[Michael Biebl]

Am 10.05.2015 um 18:38 schrieb Michael Biebl:
> Am 10.05.2015 um 18:02 schrieb Ian Campbell:
>> The unit file, which was contributed upstream, contains:
>>
>>         Requires=dev-input-by\x2dpath-platform\x2dgpio\x2dkeys\x2devent.device
>>         After=dev-input-by\x2dpath-platform\x2dgpio\x2dkeys\x2devent.device
>>         
>> I had no reason to doubt it was correct, since it seemed logical that a
>> daemon such depend on a device which it needs.
> 
> I think, that's the wrong way to approach it.
> How do you guarantee this way, that when the daemon is started, the
> hardware is present?
> 
> Requires/After will *not* wait until the hardware shows up.

I need to clarify that. systemd will create a
dev-input-by\x2dpath-platform\x2dgpio\x2dkeys\x2devent.device unit and
wait for it to become active [1]. That internal timeout is currently 90
secs after which qcontrol.service would be marked as failed.

If the hardware would become/available active after 90 secs,
qcontrol.service wouldn't be started afaik

Starting the service via SYSTEMD_WANTS has the advantage, that you only
ever start it, if the actual hardware is present and you start it at the
right time. That's why I would prefer it.


Now, there is a reason to prefer to start qcontrol.service via
multi-user.target. And that is, if other services depend on
qcontrol.service.

I don't know if this is the case for qcontrol.


Michael

[1] That's what you need the udev rule for to tag the device with "systemd"





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