bug#23170: [PATCH shepherd] Restart dependent services on service restart

[ludo@gnu.org (Ludovic Courtès)]

Hi again!  :-)

Carlo Zancanaro <carlo@zancanaro.id.au> skribis:

> I've written a patch to fix this. It's not super smart, but it should
> do the job.

I wonder if there are cases where one might want to restart a service
without restarting its dependent services.  We can probably ignore it
for now, but perhaps we’ll need to add a flag or a separate action later.

Thoughts?

> From 50dd3ef4888b04ea3b869da893b23ad69fad8971 Mon Sep 17 00:00:00 2001
> From: Carlo Zancanaro <carlo@zancanaro.id.au>
> Date: Sat, 25 Aug 2018 20:32:11 +1000
> Subject: [PATCH] service: Restart dependent services on service restart
>
> * modules/shepherd/service.scm (required-by?): New procedure.
> (stop): Return a list of canonical-names for stopped dependent services,
> including transitive dependencies.
> (action)[restart]: Start services based on the return value of stop.
> (fold-services): New procedure.
> * tests/restart.sh: New file.
> * Makefile.am (TESTS): Add tests/restart.sh.

[...]

> +# Restart test1 and make sure that both services are still running (ie. that
> +# test2 hasn't been stopped)
> +$herd restart test1
> +$herd status test1 | grep started
> +$herd status test2 | grep started
> +
> +# Now let's test with a transitive dependency
> +$herd start test3
> +$herd status test3 | grep started
> +
> +# After restarting test1 we want test3 to still be running
> +$herd restart test1
> +$herd status test1 | grep started
> +$herd status test2 | grep started
> +$herd status test3 | grep started

For clarity, should we do an explicit “herd stop test1” followed by
“herd start test1”?  I know it’s currently equivalent under the hood,
but it might be slightly clearer.  WDYT?

Otherwise it LGTM.  Thanks for addressing these longstanding issues!

Ludo’.