[bug#40274] [PATCH v2] gnu: Add kernel-module-loader-service.

[Brice Waegeneire <brice@waegenei.re>]

* doc/guix.texi (Linux Services): Add a new subsection and document the
new service and its configuration.
* gnu/services/linux.scm (kernel-module-loader-service): New procedure.
(kernel-module-loader-service-type, kernel-module-loader-configuration):
New types.
* gnu/tests/linux-modules.scm (module-loader-program): Procedure
removed.
(modules-loaded?-program): New procedure.
(run-loadable-kernel-modules-test): 'module-loader-program' procedure
replaced by the new one. New format for last arguments
[os]: Use 'kernel-module-loader-service'.
(%test-loadable-kernel-modules-0, %test-loadable-kernel-modules-1,
%test-loadable-kernel-modules-2): Use the new argument format.
---
 doc/guix.texi               | 52 +++++++++++++++++++++++++++++++
 gnu/services/linux.scm      | 61 ++++++++++++++++++++++++++++++++++++-
 gnu/tests/linux-modules.scm | 45 ++++++++++++++++-----------
 3 files changed, 140 insertions(+), 18 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 77a4b8ed71..e8ad830102 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -75,6 +75,7 @@ Copyright @copyright{} 2020 Wiktor Żelazny@*
 Copyright @copyright{} 2020 Damien Cassou@*
 Copyright @copyright{} 2020 Jakub Kądziołka@*
 Copyright @copyright{} 2020 Jack Hill@*
+Copyright @copyright{} 2020 Brice Waegeneire@*
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -25382,6 +25383,57 @@ notifications.
 @end table
 @end deftp
 
+@cindex modprobe
+@cindex kernel module loader
+@subsubsection Kernel Module Loader Service
+
+The @code{kernel-module-loader-service} provides a service to load
+kernel modules at boot.  This is especially usefull for modules that
+don't autoload and need to be manually loaded, like it's the case with
+@code{ddcci} for example.
+
+@deffn {Scheme Procedure} kernel-module-loader-service @var{modules}
+Return a service that run @command{modprobe} with arguments
+@var{modules} at boot.  For example loading the drivers provided by
+@code{ddci-driver-linux} with @code{ddcci} in debugging mode can be done
+as follow:
+
+@lisp
+(use-modules (gnu))
+(use-package-modules linux)
+(use-service-modules linux)
+(operating-system
+  ...
+  (services (cons* (kernel-module-loader-service
+                     '(("ddcci" "dyndbg")
+                       ("ddcci_backlight")))
+                   %base-services))
+  (kernel-loadable-modules (list ddcci-driver-linux)))
+@end lisp
+@end defvr
+
+@deffn {Scheme Variable} kernel-module-loader-service-type
+The service type for loading kernel modules at boot with
+@command{modprobe}, for module that can't autoload.  Its value must be a
+@code{kernel-module-loader-configuration} object, described below.
+
+@deftp {Data Type} kernel-module-loader-configuration
+The data type representing the modules to be loaded by
+@command{modprobe}.
+
+@deftp {Data Type} kernel-module-loader-configuration
+This is the configuration record for the
+@code{kernel-module-loader-service-type}.
+
+@table @asis
+@item @code{modprobe} (default: @code{(file-append kmod "/bin/modprobe"})
+The @command{modprobe} executable to use.
+
+@item @code{modules} (default: @code{'()})
+A list of list of strings specifying the modules to load with their
+optional parameters.
+@end table
+@end deftp
 
 @node Miscellaneous Services
 @subsection Miscellaneous Services
diff --git a/gnu/services/linux.scm b/gnu/services/linux.scm
index caa0326c31..da71b275f1 100644
--- a/gnu/services/linux.scm
+++ b/gnu/services/linux.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2020 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;; Copyright © 2020 Brice Waegeneire <brice@waegenei.re>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -37,7 +38,14 @@
             earlyoom-configuration-ignore-positive-oom-score-adj?
             earlyoom-configuration-show-debug-messages?
             earlyoom-configuration-send-notification-command
-            earlyoom-service-type))
+            earlyoom-service-type
+
+            kernel-module-loader-configuration
+            kernel-module-loader-configuration?
+            kernel-module-loader-configuration-modprobe
+            kernel-module-loader-configuration-modules
+            kernel-module-loader-service-type
+            kernel-module-loader-service))
 
 \f
 ;;;
@@ -123,3 +131,54 @@ representation."
     (list (service-extension shepherd-root-service-type
                              (compose list earlyoom-shepherd-service))))
    (description "Run @command{earlyoom}, the Early OOM daemon.")))
+
+;;;
+;;; Kernel module loader.
+;;;
+
+(define-record-type* <kernel-module-loader-configuration>
+  kernel-module-loader-configuration make-kernel-module-loader-configuration
+  kernel-module-loader-configuration?
+  (modprobe kernel-module-loader-configuration-modprobe ; path of the 'modprobe' command
+            (default (file-append kmod "/bin/modprobe")))
+  (modules kernel-module-loader-configuration-modules ; list of lists of strings
+           (default '())))
+
+(define kernel-module-loader-shepherd-service
+  (match-lambda
+    (($ <kernel-module-loader-configuration> modprobe modules)
+     (list
+      (shepherd-service
+       (documentation "Load kernel modules.")
+       (provision '(kernel-module-loader))
+       (respawn? #f)
+       (one-shot? #t)
+       (start
+        #~(lambda _
+            (and-map (lambda (module-with-parameters)
+                   (zero? (apply system* #$modprobe "--"
+                                 module-with-parameters)))
+                 '#$modules))))))))
+
+(define kernel-module-loader-service-type
+  (service-type
+   (name 'kernel-module-loader)
+   (description "Load kernel modules.")
+   (extensions
+    (list
+     (service-extension shepherd-root-service-type
+                        kernel-module-loader-shepherd-service)))
+   (compose concatenate)
+   (extend (lambda (config modules)
+             (kernel-module-loader-configuration
+              (inherit config)
+              (modules (append
+                        (kernel-module-loader-configuration-modules config)
+                        modules)))))
+   (default-value (kernel-module-loader-configuration))))
+
+(define* (kernel-module-loader-service modules)
+  "Return a service that loads kernel MODULES."
+  (service kernel-module-loader-service-type
+           (kernel-module-loader-configuration
+            (modules modules))))
diff --git a/gnu/tests/linux-modules.scm b/gnu/tests/linux-modules.scm
index 39e11587c6..7b820a1269 100644
--- a/gnu/tests/linux-modules.scm
+++ b/gnu/tests/linux-modules.scm
@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2019 Jakob L. Kreuze <zerodaysfordays@sdf.org>
 ;;; Copyright © 2020 Danny Milosavljevic <dannym@scratchpost.org>
+;;; Copyright © 2020 Brice Waegeneire <brice@waegenei.re>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -19,6 +20,7 @@
 
 (define-module (gnu tests linux-modules)
   #:use-module (gnu packages linux)
+  #:use-module (gnu services linux)
   #:use-module (gnu system)
   #:use-module (gnu system vm)
   #:use-module (gnu tests)
@@ -37,25 +39,31 @@
 ;;;
 ;;; Code:
 
-(define* (module-loader-program os modules)
-  "Return an executable store item that, upon being evaluated, will dry-run
-load MODULES."
+(define* (modules-loaded?-program os modules)
+  "Return an executable store item that, upon being evaluated, will verify
+that MODULES are actually loaded."
   (program-file
    "load-kernel-modules.scm"
-   (with-imported-modules (source-module-closure '((guix build utils)))
-     #~(begin
-         (use-modules (guix build utils))
-         (for-each (lambda (module)
-                     (invoke (string-append #$kmod "/bin/modprobe") "-n" "--"
-                             module))
-                   '#$modules)))))
+   #~(begin
+     (use-modules (ice-9 rdelim)
+                  (ice-9 popen))
+     (let* ((port (open-input-pipe (string-append #$kmod "/bin/lsmod")))
+            (output (read-string port))
+            (status (close-pipe port)))
+       (and-map (lambda (module) (string-contains output module))
+                '#$modules)))))
 
-(define* (run-loadable-kernel-modules-test module-packages module-names)
-  "Run a test of an OS having MODULE-PACKAGES, and modprobe MODULE-NAMES."
+(define* (run-loadable-kernel-modules-test module-packages
+                                           modules-with-parameters)
+  "Run a test of an OS having MODULE-PACKAGES, and verify that
+MODULES-WITH-PARAMETERS are loaded in memory."
   (define os
     (marionette-operating-system
      (operating-system
       (inherit (simple-operating-system))
+      (services (cons (kernel-module-loader-service modules-with-parameters)
+                      (operating-system-user-services
+                       (simple-operating-system))))
       (kernel-loadable-modules module-packages))
      #:imported-modules '((guix combinators))))
   (define vm (virtual-machine os))
@@ -75,7 +83,9 @@ load MODULES."
              marionette))
           (test-end)
           (exit (= (test-runner-fail-count (test-runner-current)) 0)))))
-  (gexp->derivation "loadable-kernel-modules" (test (module-loader-program os module-names))))
+  (gexp->derivation
+   "loadable-kernel-modules"
+   (test (modules-loaded?-program os (map car modules-with-parameters)))))
 
 (define %test-loadable-kernel-modules-0
   (system-test
@@ -88,16 +98,17 @@ with no extra modules.")
   (system-test
    (name "loadable-kernel-modules-1")
    (description "Tests loadable kernel modules facility of <operating-system>
-with one extra module.")
+with one extra module with some parameters.")
    (value (run-loadable-kernel-modules-test
            (list ddcci-driver-linux)
-           '("ddcci")))))
+           '(("ddcci" "dyndbg" "delay:120"))))))
 
 (define %test-loadable-kernel-modules-2
   (system-test
    (name "loadable-kernel-modules-2")
    (description "Tests loadable kernel modules facility of <operating-system>
-with two extra modules.")
+with two extra modules without any parameters.")
    (value (run-loadable-kernel-modules-test
            (list acpi-call-linux-module ddcci-driver-linux)
-           '("acpi_call" "ddcci")))))
+           '(("acpi_call")
+             ("ddcci"))))))
-- 
2.25.1