Subject: Re: [PATCH] Allow booting with custom shepherd package (fixed)

From: Maxime Devos <[email-masked]>
Date: Mon, 25 Jan 2021 09:48:36 +0100

Version 2 of the patch is attached. This version also uses
the custom package for /run/current-system/profile/bin/shepherd.

From b3102f72cd66dee4442596d89e29900b8215e1be Mon Sep 17 00:00:00 2001
From: Maxime Devos <[email-masked]>
Date: Fri, 22 Jan 2021 20:06:55 +0100
Subject: [PATCH] services: shepherd: allow custom 'shepherd' package

* gnu/services/shepherd.scm
  (<shepherd-configuration>): New record.
  (shepherd-boot-gexp, shepherd-root-service-type): Use it.
  (scm->go, shepherd-configuration-file): Allow passing custom
  shepherd package.
* doc/guix.texi (Shepherd Services). Document it.
---
 doc/guix.texi             | 17 ++++++++++++-
 gnu/services/shepherd.scm | 53 +++++++++++++++++++++++++++++----------
 2 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index a765b3792e..344ffcfea5 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -32707,9 +32707,24 @@ The service type for the Shepherd ``root service''---i.e., PID@tie{}1.
 
 This is the service type that extensions target when they want to create
 shepherd services (@pxref{Service Types and Services}, for an example).
-Each extension must pass a list of @code{<shepherd-service>}.
+Each extension must pass a list of @code{<shepherd-service>}. Its
+value must be a @code{shepherd-configuration}, as described below:
 @end defvr
 
+@deftp {Data Type} shepherd-configuration
+This data type represents shepherd's configuration.
+
+@table @code
+@item shepherd (default: @code{shepherd})
+The shepherd package to use.
+
+@item services (default: @code{'()})
+A list of @code{<shepherd-service>} to start.
+You should probably use the service extension
+mechanism instead (@pxref{Shepherd Services}).
+@end table
+@end deftp
+
 @defvr {Scheme Variable} %shepherd-root-service
 This service represents PID@tie{}1.
 @end defvr
diff --git a/gnu/services/shepherd.scm b/gnu/services/shepherd.scm
index d2f9776288..14a6aa14db 100644
--- a/gnu/services/shepherd.scm
+++ b/gnu/services/shepherd.scm
@@ -3,6 +3,7 @@
 ;;; Copyright © 2017 Clément Lassieur <[email-masked]>
 ;;; Copyright © 2018 Carlo Zancanaro <[email-masked]>
 ;;; Copyright © 2020 Jan (janneke) Nieuwenhuizen <[email-masked]>
+;;; Copyright © 2021 Maxime Devos <[email-masked]>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -36,7 +37,12 @@
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
-  #:export (shepherd-root-service-type
+  #:export (shepherd-configuration
+            shepherd-configuration?
+            shepherd-configuration-shepherd
+            shepherd-configuration-services
+
+            shepherd-root-service-type
             %shepherd-root-service
             shepherd-service-type
 
@@ -76,7 +82,18 @@
 ;;; Code:

-(define (shepherd-boot-gexp services)
+(define-record-type* <shepherd-configuration>
+  shepherd-configuration make-shepherd-configuration
+  shepherd-configuration?
+  (shepherd shepherd-configuration-shepherd
+            (default shepherd)) ; package
+  (services shepherd-configuration-services
+            (default '()))) ; list of <shepherd-service>
+
+(define (shepherd-boot-gexp config)
+  "Return a gexp starting the shepherd service."
+  (let ((shepherd (shepherd-configuration-shepherd config))
+        (services (shepherd-configuration-services config)))
   #~(begin
       ;; Keep track of the booted system.
       (false-if-exception (delete-file "/run/booted-system"))
@@ -95,7 +112,10 @@
       ;; Start shepherd.
       (execl #$(file-append shepherd "/bin/shepherd")
              "shepherd" "--config"
-             #$(shepherd-configuration-file services))))
+             #$(shepherd-configuration-file services #:shepherd shepherd)))))
+
+(define shepherd-packages
+  (compose list shepherd-configuration-shepherd))
 
 (define shepherd-root-service-type
   (service-type
@@ -103,20 +123,25 @@
    ;; Extending the root shepherd service (aka. PID 1) happens by
    ;; concatenating the list of services provided by the extensions.
    (compose concatenate)
-   (extend append)
+   (extend (lambda (config extra-services)
+             (shepherd-configuration
+               (inherit config)
+               (services (append (shepherd-configuration-services config)
+                                 extra-services)))))
    (extensions (list (service-extension boot-service-type
                                         shepherd-boot-gexp)
                      (service-extension profile-service-type
-                                        (const (list shepherd)))))
+                                        shepherd-packages)))
+   (default-value (shepherd-configuration))
    (description
     "Run the GNU Shepherd as PID 1---i.e., the operating system's first
 process.  The Shepherd takes care of managing services such as daemons by
 ensuring they are started and stopped in the right order.")))
 
 (define %shepherd-root-service
-  ;; The root shepherd service, aka. PID 1.  Its parameter is a list of
-  ;; <shepherd-service> objects.
-  (service shepherd-root-service-type '()))
+  ;; The root shepherd service, aka. PID 1.  Its parameter is a
+  ;; <shepherd-configuration>.
+  (service shepherd-root-service-type))
 
 (define-syntax shepherd-service-type
   (syntax-rules (description)
@@ -270,9 +295,9 @@ stored."
                                    #~(#$name #$doc #$proc)))
                                 (shepherd-service-actions service))))))))
 
-(define (scm->go file)
+(define* (scm->go file #:key (shepherd shepherd))
   "Compile FILE, which contains code to be loaded by shepherd's config file,
-and return the resulting '.go' file."
+and return the resulting '.go' file. SHEPHERD is used as shepherd package."
   (let-system (system target)
     (with-extensions (list shepherd)
       (computed-file (string-append (basename (scheme-file-name file) ".scm")
@@ -294,11 +319,13 @@ and return the resulting '.go' file."
                      #:options '(#:local-build? #t
                                  #:substitutable? #f)))))
 
-(define (shepherd-configuration-file services)
-  "Return the shepherd configuration file for SERVICES."
+(define* (shepherd-configuration-file services #:key (shepherd shepherd))
+  "Return the shepherd configuration file for SERVICES. SHEPHERD is used
+as shepherd package."
   (assert-valid-graph services)
 
-  (let ((files (map shepherd-service-file services)))
+  (let ((files (map shepherd-service-file services))
+        (scm->go (cute scm->go <> #:shepherd shepherd)))
     (define config
       #~(begin
           (use-modules (srfi srfi-34)
-- 
2.30.0