Re: [PATCH] Export udev-configuration functions.

[Ricardo Wurmus <rekado@elephly.net>]

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Ludovic Courtès <ludo@gnu.org> writes:

> We should factorize this so one can write:
>
>   (udev-rule "90-avrispmkii.rules"
>              "SUBSYSTEM != …")
>
> Because here it’s arguably sufficiently verbose to discourage newcomers.
> :-)

Patch attached.  Is this okay?


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From 77f22cb933a9740cccc62f6bac2d3f9381192eba Mon Sep 17 00:00:00 2001
From: Ricardo Wurmus <rekado@elephly.net>
Date: Wed, 18 Nov 2015 21:58:53 +0100
Subject: [PATCH] services: Add udev-rule procedure.

* gnu/services/base.scm (udev-rule): New procedure.
(kvm-udev-rule): Rewrite in terms of udev-rule.
---
 gnu/services/base.scm | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index bb5854d..1308065 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -57,6 +57,7 @@
             udev-configuration-rules
             udev-service-type
             udev-service
+            udev-rule
 
             mingetty-configuration
             mingetty-configuration?
@@ -956,12 +957,9 @@ item of @var{packages}."
                  #:modules '((guix build union)
                              (guix build utils))))
 
-(define* (kvm-udev-rule)
-  "Return a directory with a udev rule that changes the group of
-@file{/dev/kvm} to \"kvm\" and makes it #o660."
-  ;; Apparently QEMU-KVM used to ship this rule, but now we have to add it by
-  ;; ourselves.
-  (computed-file "kvm-udev-rules"
+(define (udev-rule filename contents)
+  "Return a directory with a udev rule file FILENAME containing CONTENTS."
+  (computed-file filename
                  #~(begin
                      (use-modules (guix build utils))
 
@@ -970,15 +968,22 @@ item of @var{packages}."
 
                      (mkdir-p rules.d)
                      (call-with-output-file
-                         (string-append rules.d "/90-kvm.rules")
+                         (string-append rules.d "/" #$filename)
                        (lambda (port)
-                         ;; Build users are part of the "kvm" group, so we
-                         ;; can fearlessly make /dev/kvm 660 (see
-                         ;; <http://bugs.gnu.org/18994>, for background.)
-                         (display "\
-KERNEL==\"kvm\", GROUP=\"kvm\", MODE=\"0660\"\n" port))))
+                         (display #$contents port))))
                  #:modules '((guix build utils))))
 
+(define (kvm-udev-rule)
+  "Return a directory with a udev rule that changes the group of
+@file{/dev/kvm} to \"kvm\" and makes it #o660."
+  ;; Apparently QEMU-KVM used to ship this rule, but now we have to add it by
+  ;; ourselves.
+
+  ;; Build users are part of the "kvm" group, so we can fearlessly make
+  ;; /dev/kvm 660 (see <http://bugs.gnu.org/18994>, for background.)
+  (udev-rule "90-kvm.rules"
+             "KERNEL==\"kvm\", GROUP=\"kvm\", MODE=\"0660\"\n"))
+
 (define udev-dmd-service
   ;; Return a <dmd-service> for UDEV with RULES.
   (match-lambda
-- 
2.5.0


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> That’s one way do do it.
>
> Another one would be to write an avrispmkii service that would extend
> ‘udev-service-type’ by passing it its rule (and maybe it could do other
> useful things as well?)

I did this first but then it seemed overly complicated when there
already is a service that does almost exactly what I want.  But in more
complicated cases it may make sense to add a new service.  I really like
how straight forward this new service composition feature is!

>> From 46091d6045443a1bedbd1ca37e8ac31c1399d551 Mon Sep 17 00:00:00 2001
>> From: Ricardo Wurmus <rekado@elephly.net>
>> Date: Wed, 18 Nov 2015 12:17:42 +0100
>> Subject: [PATCH] services: Export udev-configuration procedures.
>>
>> * gnu/services/base.scm (udev-configuration, udev-configuration?,
>>   udev-configuration-rules): Export.
>
> Good idea indeed.  OK!

Pushed!  Thanks!

~~ Ricardo