services: Add Shepherd 'configuration' action to various services.

* gnu/services/avahi.scm (avahi-shepherd-service): Add 'actions' field.
* gnu/services/base.scm (nscd-actions): Add call to
'shepherd-configuration-action'.
* gnu/services/desktop.scm (upower-shepherd-service): Add 'actions'
field.
(elogind-shepherd-service): Likewise.
* gnu/services/dict.scm (dicod-shepherd-service): Likewise.
* gnu/services/networking.scm (openntpd-shepherd-service): Likewise.
(tor-shepherd-service): Likewise.
* gnu/services/ssh.scm (openssh-shepherd-service): Likewise.
* gnu/services/web.scm (nginx-shepherd-service): Likewise.
* gnu/services/xorg.scm (gdm-shepherd-service): Likewise.
* gnu/tests/base.scm (run-basic-test)["nscd configuration action"]: New
test.
* doc/guix.texi (Services): Document it.

doc/guix.texi

@@ -17654,6 +17654,17 @@ Service xorg-server has been stopped.
 Service xorg-server has been started.
 @end example
 
+@cindex configuration, action for shepherd services
+@cindex configuration file, of a shepherd service
+For some services, @command{herd configuration} returns the name of the
+service's configuration file, which can be handy to inspect its
+configuration:
+
+@example
+# herd configuration sshd
+/gnu/store/@dots{}-sshd_config
+@end example
+
 The following sections document the available services, starting with
 the core services, that may be used in an @code{operating-system}
 declaration.

gnu/services/avahi.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2014, 2015, 2016, 2017, 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014-2020, 2022 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -137,7 +137,8 @@ (define (avahi-shepherd-service config)
                            #$@(if debug? #~("--debug") #~())
                            "-f" #$config)
                      #:pid-file "/run/avahi-daemon/pid"))
-           (stop #~(make-kill-destructor))))))
+           (stop #~(make-kill-destructor))
+           (actions (list (shepherd-configuration-action config)))))))
 
 (define avahi-service-type
   (let ((avahi-package (compose list avahi-configuration-avahi)))

gnu/services/base.scm

@@ -1327,10 +1327,11 @@ (define (nscd-action-procedure nscd config option)
              (loop)))))))
 
 (define (nscd-actions nscd config)
-  "Return Shepherd actions for NSCD."
+  "Return Shepherd actions for NSCD using CONFIG its config file."
   ;; Make this functionality available as actions because that's a simple way
   ;; to run the right 'nscd' binary with the right config file.
-  (list (shepherd-action
+  (list (shepherd-configuration-action config)
+        (shepherd-action
          (name 'statistics)
          (documentation "Display statistics about nscd usage.")
          (procedure (nscd-action-procedure nscd config "--statistics")))

gnu/services/desktop.scm

@@ -273,7 +273,8 @@ (define (upower-shepherd-service config)
                      #:environment-variables
                      (list (string-append "UPOWER_CONF_FILE_NAME="
                                           #$config))))
-           (stop #~(make-kill-destructor))))))
+           (stop #~(make-kill-destructor))
+           (actions (list (shepherd-configuration-action config)))))))
 
 (define upower-service-type
   (let ((upower-package (compose list upower-configuration-upower)))
@@ -1168,6 +1169,9 @@ (module (file-append (elogind-package config)
 
 (define (elogind-shepherd-service config)
   "Return a Shepherd service to start elogind according to @var{config}."
+  (define config-file
+    (elogind-configuration-file config))
+
   (list (shepherd-service
          (requirement '(dbus-system))
          (provision '(elogind))
@@ -1176,9 +1180,9 @@ (define (elogind-shepherd-service config)
                                         "/libexec/elogind/elogind"))
                    #:environment-variables
                    (list (string-append "ELOGIND_CONF_FILE="
-                                        #$(elogind-configuration-file
+                                        #$config-file))))
-                                           config)))))
+         (stop #~(make-kill-destructor))
-         (stop #~(make-kill-destructor)))))
+         (actions (list (shepherd-configuration-action config-file))))))
 
 (define elogind-service-type
   (service-type (name 'elogind)

gnu/services/dict.scm

@@ -182,7 +182,8 @@ (define (dicod-shepherd-service config)
            (stop #~(if (and (defined? 'make-inetd-destructor)
                             #$(= 1 (length interfaces))) ;XXX
                        (make-inetd-destructor)
-                       (make-kill-destructor)))))))
+                       (make-kill-destructor)))
+           (actions (list (shepherd-configuration-action dicod.conf)))))))
 
 (define dicod-service-type
   (service-type

gnu/services/networking.scm

@@ -652,7 +652,8 @@ (define ntpd.conf
                      ;; while running, leading shepherd to disable it.  To
                      ;; prevent spamming stderr, redirect output to logfile.
                      #:log-file "/var/log/ntpd.log"))
-           (stop #~(make-kill-destructor))))))
+           (stop #~(make-kill-destructor))
+           (actions (list (shepherd-configuration-action ntpd.conf)))))))
 
 (define (openntpd-service-activation config)
   "Return the activation gexp for CONFIG."
@@ -1032,6 +1033,7 @@ (define (tor-shepherd-service config)
                           (list #$tor "-f" #$torrc)
                           #:user "tor" #:group "tor"))
                 (stop #~(make-kill-destructor))
+                (actions (list (shepherd-configuration-action torrc)))
                 (documentation "Run the Tor anonymous network overlay."))))))))
 
 (define (tor-activation config)

gnu/services/ssh.scm

@@ -524,9 +524,12 @@ (define port-number
   (define max-connections
     (openssh-configuration-max-connections config))
 
+  (define config-file
+    (openssh-config-file config))
+
   (define openssh-command
     #~(list (string-append #$(openssh-configuration-openssh config) "/sbin/sshd")
-            "-D" "-f" #$(openssh-config-file config)))
+            "-D" "-f" #$config-file))
 
   (define inetd-style?
     ;; Whether to use 'make-inetd-constructor'.  That procedure appeared in
@@ -568,6 +571,7 @@ (define ipv6-support?
          (stop #~(if #$inetd-style?
                      (make-inetd-destructor)
                      (make-kill-destructor)))
+         (actions (list (shepherd-configuration-action config-file)))
          (auto-start? (openssh-auto-start? config)))))
 
 (define (openssh-pam-services config)

gnu/services/web.scm

@@ -790,13 +790,11 @@ (define (nginx-shepherd-service config)
                 (nginx file run-directory shepherd-requirement)
    (let* ((nginx-binary (file-append nginx "/sbin/nginx"))
           (pid-file (in-vicinity run-directory "pid"))
+          (config-file (or file (default-nginx-config config)))
           (nginx-action
            (lambda args
              #~(lambda _
-                 (invoke #$nginx-binary "-c"
+                 (invoke #$nginx-binary "-c" #$config-file #$@args)
-                         #$(or file
-                               (default-nginx-config config))
-                         #$@args)
                  (match '#$args
                    (("-s" . _) #f)
                    (_
@@ -817,6 +815,7 @@ (define (nginx-shepherd-service config)
             (stop (nginx-action "-s" "stop"))
             (actions
               (list
+               (shepherd-configuration-action config-file)
                (shepherd-action
                  (name 'reload)
                  (documentation "Reload nginx configuration file and restart worker processes.

gnu/services/xorg.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2017 Andy Wingo <wingo@igalia.com>
-;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013-2017, 2019-2020, 2022 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2015 Sou Bunnbu <iyzsong@gmail.com>
 ;;; Copyright © 2018, 2019 Timothy Sample <samplet@ngyro.com>
 ;;; Copyright © 2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
@@ -1083,6 +1083,9 @@ (module "pam_permit.so")))))
                      (gdm-configuration-allow-empty-passwords? config))))
 
 (define (gdm-shepherd-service config)
+  (define config-file
+    (gdm-configuration-file config))
+
   (list (shepherd-service
          (documentation "Xorg display server (GDM)")
          (provision '(xorg-server))
@@ -1095,9 +1098,7 @@ (define (gdm-shepherd-service config)
                      (list #$@(if (gdm-configuration-auto-suspend? config)
                                   #~()
                                   #~("DCONF_PROFILE=/etc/dconf/profile/gdm"))
-                           (string-append
+                           (string-append "GDM_CUSTOM_CONF=" #$config-file)
-                            "GDM_CUSTOM_CONF="
-                            #$(gdm-configuration-file config))
                            (string-append
                             "GDM_DBUS_DAEMON="
                             #$(gdm-configuration-dbus-daemon config))
@@ -1129,6 +1130,7 @@ (define (gdm-shepherd-service config)
                             "GDM_WAYLAND_SESSION="
                             #$(gdm-configuration-wayland-session config))))))
          (stop #~(make-kill-destructor))
+         (actions (list (shepherd-configuration-action config-file)))
          (respawn? #t))))
 
 (define gdm-polkit-rules

gnu/tests/base.scm

@@ -424,6 +424,12 @@ (define (entry->list entry)
               (x
                (pk 'failure x #f))))
 
+          (test-assert "nscd configuration action"
+            (marionette-eval '(with-shepherd-action 'nscd ('configuration)
+                                                    results
+                                (file-exists? (car results)))
+                             marionette))
+
           (test-equal "nscd invalidate action"
             '(#t)                                 ;one value, #t
             (marionette-eval '(with-shepherd-action 'nscd ('invalidate "hosts")