services: Add modem-manager-service-type.

* gnu/services/networking.scm (modem-manager-service-type): New variable.
(<modem-manager-configuration>): New variable.
(modem-manager-configuration): New procedure.
(modem-manager-configuration?): New procedure.
* doc/guix.texi (Networking Services): Document it.
* gnu/tests/networking.scm: Import (gnu services base).

doc/guix.texi

@@ -10773,6 +10773,28 @@ several commands to interact with the daemon and configure networking:
 and @command{wicd-curses} user interfaces.
 @end deffn
+@cindex ModemManager
+
+@defvr {Scheme Variable} modem-manager-service-type
+This is the service type for the
+@uref{https://wiki.gnome.org/Projects/ModemManager, ModemManager}
+service. The value for this service type is a
+@code{modem-manager-configuration} record.
+
+This service is part of @code{%desktop-services} (@pxref{Desktop
+Services}).
+@end defvr
+
+@deftp {Data Type} modem-manager-configuration
+Data type representing the configuration of ModemManager.
+
+@table @asis
+@item @code{modem-manager} (default: @code{modem-manager})
+The ModemManager package to use.
+
+@end table
+@end deftp
+
 @cindex NetworkManager
 @defvr {Scheme Variable} network-manager-service-type

gnu/services/networking.scm

@@ -31,6 +31,7 @@ (define-module (gnu services networking)
   #:use-module (gnu system pam)
   #:use-module (gnu packages admin)
   #:use-module (gnu packages connman)
+  #:use-module (gnu packages freedesktop)
   #:use-module (gnu packages linux)
   #:use-module (gnu packages tor)
   #:use-module (gnu packages messaging)
@@ -92,6 +93,9 @@ (define-module (gnu services networking)
             connman-configuration?
             connman-service-type
 
+            modem-manager-configuration
+            modem-manager-configuration?
+            modem-manager-service-type
             wpa-supplicant-service-type
 
             openvswitch-service-type
@@ -809,6 +813,17 @@ (define* (wicd-service #:key (wicd wicd))
 and @command{wicd-curses} user interfaces."
   (service wicd-service-type wicd))
 
+
+;;;
+;;; ModemManager
+;;;
+
+(define-record-type* <modem-manager-configuration>
+  modem-manager-configuration make-modem-manager-configuration
+  modem-manager-configuration?
+  (modem-manager modem-manager-configuration-modem-manager
+                   (default modem-manager)))
+
 
 ;;;
 ;;; NetworkManager
@@ -946,6 +961,30 @@ (define connman-service-type
                    "Run @url{https://01.org/connman,Connman},
 a network connection manager."))))
 
+
+;;;
+;;; Modem manager
+;;;
+
+(define modem-manager-service-type
+  (let ((config->package
+         (match-lambda
+          (($ <modem-manager-configuration> modem-manager)
+           (list modem-manager)))))
+    (service-type (name 'modem-manager)
+                  (extensions
+                   (list (service-extension dbus-root-service-type
+                                            config->package)
+                         (service-extension udev-service-type
+                                            config->package)
+                         (service-extension polkit-service-type
+                                            config->package)))
+                  (default-value (modem-manager-configuration))
+                  (description
+                   "Run @uref{https://wiki.gnome.org/Projects/ModemManager,
+ModemManager}, a modem management daemon that aims to simplify dialup
+networking."))))
+
 
 ;;;
 ;;; WPA supplicant

gnu/tests/networking.scm

@@ -22,6 +22,7 @@ (define-module (gnu tests networking)
   #:use-module (gnu system)
   #:use-module (gnu system vm)
   #:use-module (gnu services)
+  #:use-module (gnu services base)
   #:use-module (gnu services networking)
   #:use-module (guix gexp)
   #:use-module (guix store)