bug#26830: Allow services to implement a 'reload' action

[Ludovic Courtès]

Hello!

Mathieu Othacehe <address@hidden> skribis:

>> Services do not have to implement 'reload' and if, say, foo-daemon
>> doesn't implement it, 'herd reload foo-daemon' will return 1 and display
>> a message saying that foo-deamon does not have an action 'reload'.
>> That's the reason of the #f default value.
>>
>> WDYT?
>
> Your whole serie LGTM for me !

Same here, really happy to see this addressed!

> I have just one small concern, there is a already a "reload" action on
> shepherd root service.

Right, but that’s just for ‘root’, not for the other services.

However, I think ‘reload’ might be confusing since in fact it doesn’t
load Scheme code, contrary to what “herd load root foo.scm” does (maybe
that’s what you meant?).  In fact it’s closer to what “herd restart
foo” does.

What about changing the name to ‘reconfigure’ or ‘upgrade’ to avoid the
confusion?

The logical next step of this series will be to have the service upgrade
code in ‘guix system reconfigure’ invoke this action when it is defined.
That will be awesome.

Some comments:

+                      #:actions (make-actions
+                                 (reload
+                                  "Reload the service's configuration files."
+                                  #$(shepherd-service-reload service))))))))

Here I think we should only define the action when it has a non-#f
value.  That way we can distinguish between services that have a useful
reload/reconfigure/upgrade action and those that don’t; in the latter
case, we simply use ‘restart’ when upgrading.

Regarding nginx:

+              (stop (nginx-action "-s" "stop"))
+              (reload (nginx-action "-s" "reload"))))))))

Is this of any use in practice?  The nginx command line is something
like:

  /gnu/store/74kz9m850ycxpzkg6dvn9wbd3xjkwwrb-nginx-1.12.0/sbin/nginx -c 
/gnu/store/5w11ahw113fndvab3xmwcjzs2rw56sbh-nginx-config/bayfront.conf -p 
/var/run/nginx

and the configuration file in /gnu/store is immutable, so “nginx -s
reload” does nothing.  If the action took an argument, we could do:

  herd reconfigure nginx /gnu/store/…-new-config.conf

which would translate to:

  nginx -s reload -c /gnu/store/…-new-config.conf

Probably our best option.

Otherwise, I think we’d have to move the config to a fixed location, say
/etc/nginx, for “nginx -s reload” to have any effect.  However I don’t
quite like the use of /etc.  Thoughts?

Does Dovecot have the same problem?

Thank you!

Ludo’.