services: Add btrbk-service-type.

* rosenthal/services/file-systems.scm: New file.
(<btrbk-configuration>): New data type.
(btrbk-etc-service,btrbk-mcron-jobs): New procedures.
(btrbk-service-type): New variable.

rosenthal/services/file-systems.scm

@@ -0,0 +1,42 @@
+(define-module (rosenthal services file-systems)
+  #:use-module (guix gexp)
+  #:use-module (gnu packages backup)
+  #:use-module (gnu services)
+  #:use-module (gnu services configuration)
+  #:use-module (gnu services mcron)
+  #:export (btrbk-service-type
+            btrbk-configuration))
+
+
+;;
+;; Btrbk
+;;
+
+
+(define-configuration btrbk-configuration
+  (btrbk
+   (file-like btrbk)
+   "@code{btrbk} package to use.")
+  (config-file
+   (file-like (plain-file "empty" ""))
+   "File-like object for btrbk configuration, see also @code{btrbk.conf(5)}.")
+  (no-serialization))
+
+(define (btrbk-etc-service config)
+  `(("btrbk/btrbk.conf" ,(btrbk-configuration-config-file config))))
+
+(define (btrbk-mcron-jobs config)
+  (list #~(job next-hour-from
+               #$(file-append (btrbk-configuration-btrbk config)
+                              "/bin/btrbk run --quiet"))))
+
+(define btrbk-service-type
+  (service-type
+   (name 'btrbk)
+   (extensions
+    (list (service-extension etc-service-type
+                             btrbk-etc-service)
+          (service-extension mcron-service-type
+                             btrbk-mcron-jobs)))
+   (default-value (btrbk-configuration))
+   (description "Configure and run btrbk hourly.")))