gnu: udev-service-type: accept hardware description file extensions.

The udev-configuration record now has a hardware field.

The contents of the /etc/udev directory now includes hwdb.bin, which is
computed when the system is instanciated (prior to system activation).  The
hardware description files used to generate hwdb.bin are not installed in
/etc, because they are not required at run-time.

The documentation has been reworked so as to explain why creating udev rules
or hardware needs helper functions for configuration or extension.

* gnu/services/base.scm (udev-hardware): New function.
(file->udev-hardware): New function.
(udev-hardware-service): New function.
(udev-etc): Add hwdb.d and hwdb.bin.
(module): Export udev-hardware, file->udev-hardware, and udev-hardware-service.
(<udev-configuration>): Add the native-udev field.
(udev-service-type) [extend]: Populate the hardware field.
* doc/guix.texi (Base Services)[udev-service-type]: Explain configuration and
extension values.
* doc/guix.texi (Base Services)[udev-hardware]: Document it.
[udev-hardware-service]: Same.
* doc/guix.texi (Base Services)[udev-configuration]: Document the native-udev
field.

1 files changed, 58 insertions, 14 deletions

diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index 10e7383475..db22ac848e 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -82,6 +82,7 @@
                 #:select (mount-flags->bit-mask
                           swap-space->flags-bit-mask))
   #:use-module (guix gexp)
+  #:use-module ((guix packages) #:select (package-version))
   #:use-module (guix records)
   #:use-module (guix modules)
   #:use-module (guix pki)
@@ -152,11 +153,15 @@
             udev-configuration
             udev-configuration?
             udev-configuration-rules
+            udev-configuration-hardware
             udev-service-type
             udev-service  ; deprecated
             udev-rule
+            udev-hardware
             file->udev-rule
+            file->udev-hardware
             udev-rules-service
+            udev-hardware-service
 
             login-configuration
             login-configuration?
@@ -2232,10 +2237,12 @@ command that allows you to share pre-built binaries with others over HTTP.")))
   (udev   udev-configuration-udev                 ;file-like
           (default eudev))
   (rules  udev-configuration-rules                ;list of file-like
-          (default '())))
+          (default '()))
+  (hardware  udev-configuration-hardware          ;list of file-like
+             (default '())))
 
 (define (udev-configurations-union subdirectory packages)
-  "Return the union of the lib/udev/SUBDIRECTORY.d directories found in each
+  "Return the union of the lib/udev/SUBDIRECTORY directories found in each
 item of PACKAGES."
   (define build
     (with-imported-modules '((guix build union)
@@ -2247,8 +2254,8 @@ item of PACKAGES."
                        (srfi srfi-26))
 
           (define %standard-locations
-            '(#$(string-append "/lib/udev/" subdirectory ".d")
-                #$(string-append "/libexec/udev/" subdirectory ".d")))
+            '(#$(string-append "/lib/udev/" subdirectory)
+                #$(string-append "/libexec/udev/" subdirectory)))
 
           (define (configuration-sub-directory directory)
             ;; Return the sub-directory of DIRECTORY containing udev
@@ -2264,7 +2271,7 @@ item of PACKAGES."
 (define (udev-rules-union packages)
   "Return the union of the lib/udev/rules.d directories found in each
 item of PACKAGES."
-  (udev-configurations-union "rules" packages))
+  (udev-configurations-union "rules.d" packages))
 
 (define (udev-configuration-file subdirectory file-name contents)
   "Return a directory with a udev configuration file FILE-NAME containing CONTENTS."
@@ -2272,7 +2279,11 @@ item of PACKAGES."
 
 (define (udev-rule file-name contents)
   "Return a directory with a udev rule file FILE-NAME containing CONTENTS."
-  (udev-configuration-file "rules" file-name contents))
+  (udev-configuration-file "rules.d" file-name contents))
+
+(define (udev-hardware file-name contents)
+  "Return a directory with a udev hardware file FILE-NAME containing CONTENTS."
+  (udev-configuration-file "hwdb.d" file-name contents))
 
 (define (file->udev-configuration-file subdirectory file-name file)
   "Return a directory with a udev configuration file FILE-NAME which is a copy
@@ -2285,8 +2296,7 @@ item of PACKAGES."
                        (define configuration-directory
                          (string-append #$output
                                         "/lib/udev/"
-                                        #$subdirectory
-                                        ".d"))
+                                        #$subdirectory))
 
                        (define file-copy-dest
                          (string-append configuration-directory "/" #$file-name))
@@ -2296,7 +2306,11 @@ item of PACKAGES."
 
 (define (file->udev-rule file-name file)
   "Return a directory with a udev rule file FILE-NAME which is a copy of FILE."
-  (file->udev-configuration-file "rules" file-name file))
+  (file->udev-configuration-file "rules.d" file-name file))
+
+(define (file->udev-hardware file-name file)
+  "Return a directory with a udev hardware file FILE-NAME which is a copy of FILE."
+  (file->udev-configuration-file "hwdb.d" file-name file))
 
 (define kvm-udev-rule
   ;; Return a directory with a udev rule that changes the group of /dev/kvm to
@@ -2405,13 +2419,27 @@ item of PACKAGES."
 
 (define (udev-etc config)
   (match-record config <udev-configuration>
-    (udev rules)
+    (udev rules hardware)
+    (let* ((hardware
+            (udev-configurations-union "hwdb.d" (cons* udev hardware)))
+           (hwdb.bin
+            (computed-file
+             "hwdb.bin"
+             (with-imported-modules '((guix build utils))
+               #~(begin
+                   (use-modules (guix build utils))
+                   (setenv "UDEV_HWDB_PATH" #$hardware)
+                   (invoke #+(file-append udev "/bin/udevadm")
+                           "hwdb"
+                           "--update"
+                           "-o" #$output))))))
     `(("udev"
        ,(file-union "udev"
                     `(("udev.conf" ,udev.conf)
                       ("rules.d"
                        ,(udev-rules-union (cons* udev kvm-udev-rule
-                                                 rules)))))))))
+                                                 rules)))
+                      ("hwdb.bin" ,hwdb.bin))))))))
 
 (define udev-service-type
   (service-type (name 'udev)
@@ -2420,12 +2448,15 @@ item of PACKAGES."
                                           udev-shepherd-service)
                        (service-extension etc-service-type udev-etc)))
                 (compose concatenate)           ;concatenate the list of rules
-                (extend (lambda (config rules)
+                (extend (lambda (config extensions)
                           (let ((initial-rules
-                                 (udev-configuration-rules config)))
+                                 (udev-configuration-rules config))
+                                (initial-hardware
+                                 (udev-configuration-hardware config)))
                             (udev-configuration
                              (inherit config)
-                             (rules (append initial-rules rules))))))
+                             (rules (append initial-rules extensions))
+                             (hardware (append initial-hardware extensions))))))
                 (default-value (udev-configuration))
                 (description
                  "Run @command{udev}, which populates the @file{/dev}
@@ -2460,6 +2491,19 @@ instance."
                 (description "This service adds udev rules."))))
     (service type #f)))
 
+(define (udev-hardware-service name hardware-files)
+  "Return a service that extends udev-service-type with HARDWARE-FILES, named
+NAME-udev-hardware."
+  (let* ((name (symbol-append name '-udev-hardware))
+         (udev-extension (const (list hardware-files)))
+         (type (service-type
+                (name name)
+                (extensions (list
+                             (service-extension
+                              udev-service-type udev-extension)))
+                (description "This service adds udev hardware files."))))
+    (service type #f)))
+
 (define (swap-space->shepherd-service-name space)
   (let ((target (swap-space-target space)))
     (symbol-append 'swap-