Start upon existence of multiple devices

[Scott James Remnant]

In general, this is the exact use case (multiple devices come up in an
unknown order) for which the current behavior of "and" is intended
for.

  start on device_a and device_b

Would be the simplest expression, and the side-effects that you
usually try and avoid with "and" are probably exactly what you want in
this case.

In practice, you may want to put the device requirements in a
process-less conf file which you can reference with "started
mythtv_required_devices" or similar to abstract it out a bit.  This
would make the multiple-deps problem easier to manage too.

Scott

On Sun, Feb 6, 2011 at 1:18 AM, Jan Ceuleers <jan.ceuleers at computer.org> wrote:
> Hi.
>
> I have a howto question. If there is somewhere else more appropriate to such
> questions then feel free to point me there.
>
> I have a task that should not be started until multiple devices have been
> registered. In the general case the order in which these devices come up
> after boot is unknown and may differ from one boot to the next (e.g.
> depending on whether the devices have retained their firmware).
>
> The specific use cases I have in mind are the following:
>
> 1. The MythTV master backend process should not be started until networking
> is up, and the mysql server is up, and all configured video capture devices
> are ready for use.
>
> 2. The MythTV slave backend process should not be started until networking
> is up and all configured video capture devices are ready for use.
>
> So there are multiple problems:
>
> A. The problem pointed out above with regard to a dependency on multiple
> devices;
>
> B. The fact that, at the moment, the /etc/init/mythtv-backend.conf file is
> generic rather than taking the above dependencies into account, knowing that
> they differ depending on the use case and available video capture devices.
> So ideally a way is needed to automatically generate the .conf file.
>
> Thanks, Jan
>
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