services: log-cleanup: Rewrite as a Shepherd timer.

This is a semi-incompatible change: gexps previously provided in the
‘schedule’ field will no longer work.

* gnu/services/admin.scm (log-cleanup-mcron-jobs): Remove.
(log-cleanup-shepherd-services): New procedure.
(log-cleanup-service-type): Extend SHEPHERD-ROOT-SERVICE-TYPE instead of
MCRON-SERVICE-TYPE.
* doc/guix.texi (Log Rotation): Adjust ‘schedule’ documentation
accordingly.

Change-Id: I2a3beb7dffbc9992b714a29423674db9c7dc6cab

doc/guix.texi

@@ -21085,8 +21085,9 @@ Age in seconds after which a file is subject to deletion (six months by
 default).
 
 @item @code{schedule} (default: @code{"30 12 01,08,15,22 * *"})
-String or gexp denoting the corresponding mcron job schedule
-(@pxref{Scheduled Job Execution}).
+Schedule of the log cleanup job written either as a string in
+traditional cron syntax or as a gexp representing a Shepherd calendar
+event (@pxref{Timers,,, shepherd, The GNU Shepherd Manual}).
 @end table
 @end deftp
 

gnu/services/admin.scm

@@ -385,18 +385,31 @@ (define (log-cleanup-program directory expiry)
                                 (length logs) #$directory)
                         (for-each delete-file logs))))))
 
-(define (log-cleanup-mcron-jobs configuration)
+(define (log-cleanup-shepherd-services configuration)
   (match-record configuration <log-cleanup-configuration>
                 (directory expiry schedule)
-    (list #~(job #$schedule
-                 #$(log-cleanup-program directory expiry)))))
+    (let ((program (log-cleanup-program directory expiry)))
+      (list (shepherd-service
+             (provision '(log-cleanup))
+             (requirement '(user-processes))
+             (modules '((shepherd service timer)))
+             (start #~(make-timer-constructor
+                       #$(if (string? schedule)
+                             #~(cron-string->calendar-event #$schedule)
+                             schedule)
+                       (command '(#$program))))
+             (stop #~(make-timer-destructor))
+             (actions (list (shepherd-action
+                             (name 'trigger)
+                             (documentation "Trigger log cleanup.")
+                             (procedure #~trigger-timer)))))))))
 
 (define log-cleanup-service-type
   (service-type
    (name 'log-cleanup)
    (extensions
-    (list (service-extension mcron-service-type
-                             log-cleanup-mcron-jobs)))
+    (list (service-extension shepherd-root-service-type
+                             log-cleanup-shepherd-services)))
    (description
     "Periodically delete old log files.")))