[bug#62465] [PATCH v4 1/3] services: mcron: Add 'shepherd-requirement' field.

[Bruno Victal <mirai@makinata.eu>]

* gnu/services/mcron.scm (mcron-configuration)[shepherd-requirement]: New field.
(list-of-symbols?): New predicate.
(mcron-shepherd-services): Add support for additional shepherd requirements.
* doc/guix.texi (Scheduled Job Execution): Update it.
---

Notable changes since v3:
* Implemented adjustable user, group and supplementary groups for mcron service.
  These are especially useful when configuring multiple instances. This also aligns
  with upstream recommendation to run multiple mcron instances with lesser
  privileged accounts.

Quoting mcron commit 0fe4d2cc9544d24ecc3e74a2d92433e01b9e25c6:
> I don't believe that anyone should be running system-wide cron processes these
> days (the attack surface is rather large), but should use separate per-user or
> per-service mcron daemon processes.

Tested with 'make check-system TESTS=mcron'.

 doc/guix.texi          |  4 ++++
 gnu/services/mcron.scm | 13 +++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index a58ea8f9ec..56aa86118a 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -19379,6 +19379,10 @@ Scheduled Job Execution
 @item @code{mcron} (default: @code{mcron}) (type: file-like)
 The mcron package to use.
 
+@item @code{shepherd-requirement} (default: @code{()}) (type: list-of-symbols)
+This is a list of symbols naming Shepherd services that this service
+will depend on.
+
 @item @code{jobs} (default: @code{()}) (type: list-of-gexps)
 This is a list of gexps (@pxref{G-Expressions}), where each gexp
 corresponds to an mcron job specification (@pxref{Syntax, mcron job
diff --git a/gnu/services/mcron.scm b/gnu/services/mcron.scm
index 2ef5980e09..99eb0edd60 100644
--- a/gnu/services/mcron.scm
+++ b/gnu/services/mcron.scm
@@ -32,6 +32,7 @@ (define-module (gnu services mcron)
   #:export (mcron-configuration
             mcron-configuration?
             mcron-configuration-mcron
+            mcron-configuration-shepherd-requirement
             mcron-configuration-jobs
             mcron-configuration-log?
             mcron-configuration-log-file
@@ -58,6 +59,9 @@ (define-module (gnu services mcron)
 (define list-of-gexps?
   (list-of gexp?))
 
+(define list-of-symbols?
+  (list-of symbol?))
+
 (define-maybe/no-serialization string)
 
 (define-configuration/no-serialization mcron-configuration
@@ -65,6 +69,11 @@ (define-configuration/no-serialization mcron-configuration
    (file-like mcron)
    "The mcron package to use.")
 
+  (shepherd-requirement
+   (list-of-symbols '())
+   "This is a list of symbols naming Shepherd services that this service
+will depend on.")
+
   (jobs
    (list-of-gexps '())
    "This is a list of gexps (@pxref{G-Expressions}), where each gexp
@@ -158,13 +167,13 @@ (define (shepherd-schedule-action mcron files)
 
 (define (mcron-shepherd-services config)
   (match-record config <mcron-configuration>
-    (mcron jobs log? log-file log-format date-format)
+    (mcron shepherd-requirement jobs log? log-file log-format date-format)
     (if (eq? jobs '())
         '()                             ;nothing to do
         (let ((files (job-files mcron jobs)))
           (list (shepherd-service
                  (provision '(mcron))
-                 (requirement '(user-processes))
+                 (requirement `(user-processes ,@shepherd-requirement))
                  (modules `((srfi srfi-1)
                             (srfi srfi-26)
                             (ice-9 popen) ;for the 'schedule' action
-- 
2.39.1