services: shepherd: 'shepherd-service-type' requires documentation.

* gnu/services/shepherd.scm (shepherd-service-type): Require a
'description' form.
* gnu/services/base.scm (root-file-system-service-type)
(rngd-service-type, host-name-service-type):
(virtual-terminal-service-type, console-keymap-service-type)
(syslog-service-type, swap-service-type)
(kmscon-service-type): Add description.
* gnu/services/networking.scm (dhcp-client-service-type): Likewise.
* gnu/system/install.scm (cow-store-service-type): Likewise.
* gnu/system/linux-container.scm (dummy-networking-service-type):
Likewise.
* gnu/system/mapped-devices.scm (device-mapping-service-type):
Likewise.
* tests/guix-system.sh: Likewise.

gnu/services/base.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2015, 2016 Alex Kost <alezost@gmail.com>
 ;;; Copyright © 2015, 2016, 2020 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2015 Sou Bunnbu <iyzsong@gmail.com>
@@ -279,7 +279,9 @@ system objects.")))
 
 (define root-file-system-service-type
   (shepherd-service-type 'root-file-system
-                         (const %root-file-system-shepherd-service)))
+                         (const %root-file-system-shepherd-service)
+                         (description "Take care of syncing the root file
+system and of remounting it read-only when the system shuts down.")))
 
 (define (root-file-system-service)
   "Return a service whose sole purpose is to re-mount read-only the root file
@@ -570,7 +572,9 @@ down.")))
         (requirement '(udev))
         (provision '(trng))
         (start #~(make-forkexec-constructor '#$rngd-command))
-        (stop #~(make-kill-destructor))))))
+        (stop #~(make-kill-destructor))))
+    (description "Run the @command{rngd} random number generation daemon to
+supply entropy to the kernel's pool.")))
 
 (define* (rngd-service #:key
                        (rng-tools rng-tools)
@@ -597,7 +601,8 @@ to add @var{device} to the kernel's entropy pool.  The service will fail if
       (provision '(host-name))
       (start #~(lambda _
                  (sethostname #$name)))
-      (one-shot? #t)))))
+      (one-shot? #t)))
+   (description "Initialize the machine's host name.")))
 
 (define (host-name-service name)
   "Return a service that sets the host name to @var{name}."
@@ -626,7 +631,8 @@ to add @var{device} to the kernel's entropy pool.  The service will fail if
                          (display 1 port))))
                    #t))
         (stop #~(const #f)))))
-   #t))                                           ;default to UTF-8
+   #t                                             ;default to UTF-8
+   (description "Ensure the Linux virtual terminals run in UTF-8 mode.")))
 
 (define console-keymap-service-type
   (shepherd-service-type
@@ -638,7 +644,10 @@ to add @var{device} to the kernel's entropy pool.  The service will fail if
       (start #~(lambda _
                  (zero? (system* #$(file-append kbd "/bin/loadkeys")
                                  #$@files))))
-      (respawn? #f)))))
+      (respawn? #f)))
+   (description "@emph{This service is deprecated in favor of the
+@code{keyboard-layout} field of @code{operating-system}.}  Load the given list
+of console keymaps with @command{loadkeys}.")))
 
 (define-deprecated (console-keymap-service #:rest files)
   #f
@@ -1341,7 +1350,9 @@ Service Switch}, for an example."
                          (pid  (spawn)))
                      (umask mask)
                      pid))))
-      (stop #~(make-kill-destructor))))))
+      (stop #~(make-kill-destructor))))
+   (description "Run the syslog daemon, @command{syslogd}, which is
+responsible for logging system messages.")))
 
 ;; Snippet adapted from the GNU inetutils manual.
 (define %default-syslog.conf
@@ -2207,7 +2218,8 @@ instance."
                     (when device
                       (restart-on-EINTR (swapoff device)))
                     #f)))
-        (respawn? #f))))))
+        (respawn? #f))))
+   (description "Turn on the virtual memory swap area.")))
 
 (define (swap-service device)
   "Return a service that uses @var{device} as a swap device."
@@ -2321,7 +2333,9 @@ This service is not part of @var{%base-services}."
         (requirement '(user-processes udev dbus-system))
         (provision (list (symbol-append 'term- (string->symbol virtual-terminal))))
         (start #~(make-forkexec-constructor #$kmscon-command))
-        (stop #~(make-kill-destructor)))))))
+        (stop #~(make-kill-destructor)))))
+   (description "Start the @command{kmscon} virtual terminal emulator for the
+Linux @dfn{kernel mode setting} (KMS).")))
 
 (define-record-type* <static-networking>
   static-networking make-static-networking

gnu/services/networking.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2016, 2018, 2020 Efraim Flashner <efraim@flashner.co.il>
 ;;; Copyright © 2016 John Darrington <jmd@gnu.org>
@@ -283,7 +283,9 @@ fe80::1%lo0 apps.facebook.com\n")
                    (and (zero? (cdr (waitpid pid)))
                         (read-pid-file #$pid-file)))))
       (stop #~(make-kill-destructor))))
-   isc-dhcp))
+   isc-dhcp
+   (description "Run @command{dhcp}, a Dynamic Host Configuration
+Protocol (DHCP) client, on all the non-loopback network interfaces.")))
 
 (define-deprecated (dhcp-client-service #:key (dhcp isc-dhcp))
   dhcp-client-service-type

gnu/services/shepherd.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013, 2014, 2015, 2016, 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014, 2015, 2016, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2017 Clément Lassieur <clement@lassieur.org>
 ;;; Copyright © 2018 Carlo Zancanaro <carlo@zancanaro.id.au>
 ;;; Copyright © 2020 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
@@ -119,23 +119,25 @@ ensuring they are started and stopped in the right order.")))
   (service shepherd-root-service-type '()))
 
 (define-syntax shepherd-service-type
-  (syntax-rules ()
+  (syntax-rules (description)
     "Return a <service-type> denoting a simple shepherd service--i.e., the type
 for a service that extends SHEPHERD-ROOT-SERVICE-TYPE and nothing else.  When
 DEFAULT is given, use it as the service's default value."
-    ((_ service-name proc default)
+    ((_ service-name proc default (description text))
      (service-type
       (name service-name)
       (extensions
        (list (service-extension shepherd-root-service-type
                                 (compose list proc))))
-      (default-value default)))
+      (default-value default)
-    ((_ service-name proc)
+      (description text)))
+    ((_ service-name proc (description text))
      (service-type
       (name service-name)
       (extensions
        (list (service-extension shepherd-root-service-type
-                                (compose list proc))))))))
+                                (compose list proc))))
+      (description text)))))
 
 (define %default-imported-modules
   ;; Default set of modules imported for a service's consumption.

gnu/system/install.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, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2016 Andreas Enge <andreas@enge.fr>
 ;;; Copyright © 2017 Marius Bakke <mbakke@fastmail.com>
@@ -212,7 +212,9 @@ the given target.")
                 ;; 'user-processes' doesn't depend on us.  The 'user-file-systems'
                 ;; service will unmount TARGET eventually.
                 (delete-file-recursively
-                 (string-append target #$%backing-directory))))))))
+                 (string-append target #$%backing-directory))))))
+   (description "Make the store copy-on-write, with writes going to \
+the given target.")))
 
 (define (cow-store-service)
   "Return a service that makes the store copy-on-write, such that writes go to

gnu/system/linux-container.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015 David Thompson <davet@gnu.org>
-;;; Copyright © 2016, 2017, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016, 2017, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2019 Arun Isaac <arunisaac@systemreboot.net>
 ;;; Copyright © 2020 Efraim Flashner <efraim@flashner.co.il>
 ;;; Copyright © 2020 Google LLC
@@ -76,7 +76,10 @@ from OS that are needed on the bare metal and not in a container."
 doing anything.")
            (provision '(loopback networking))
            (start #~(const #t))))
-   #f))
+   #f
+   (description "Provide loopback and networking without actually doing
+anything.  This service is used by guest systems running in containers, where
+networking support is provided by the host.")))
 
 (define %nscd-container-caches
   ;; Similar to %nscd-default-caches but with smaller cache sizes. This allows

gnu/system/mapped-devices.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, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2016 Andreas Enge <andreas@enge.fr>
 ;;; Copyright © 2017, 2018 Mark H Weaver <mhw@netris.org>
 ;;;
@@ -130,7 +130,8 @@ specifications to 'targets'."
        (documentation "Map a device node using Linux's device mapper.")
        (start #~(lambda () #$(open source targets)))
        (stop #~(lambda _ (not #$(close source targets))))
-       (respawn? #f))))))
+       (respawn? #f))))
+   (description "Map a device node using Linux's device mapper.")))
 
 (define (device-mapping-service mapped-device)
   "Return a service that sets up @var{mapped-device}."

tests/guix-system.sh

@@ -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, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 # Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
 # Copyright © 2018 Chris Marusich <cmmarusich@gmail.com>
 #
@@ -204,7 +204,8 @@ cat > "$tmpfile" <<EOF
       (shepherd-service
         (provision '(buggy!))
         (requirement '(does-not-exist))
-        (start #t)))))
+        (start #t)))
+    (description "Buggy.")))
 
 (operating-system
   $OS_BASE