gnu: Add sound service.

* gnu/services/sound.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add this.
* doc/guix.texi (Sound Services): New chapter.

doc/guix.texi

@@ -235,6 +235,7 @@ Services
 * X Window::                    Graphical display.
 * Printing Services::           Local and remote printer support.
 * Desktop Services::            D-Bus and desktop services.
+* Sound Services::              ALSA and Pulseaudio services.
 * Database Services::           SQL databases, key-value stores, etc.
 * Mail Services::               IMAP, POP3, SMTP, and all that.
 * Messaging Services::          Messaging services.
@@ -9697,6 +9698,7 @@ declaration.
 * X Window::                    Graphical display.
 * Printing Services::           Local and remote printer support.
 * Desktop Services::            D-Bus and desktop services.
+* Sound Services::              ALSA and Pulseaudio services.
 * Database Services::           SQL databases, key-value stores, etc.
 * Mail Services::               IMAP, POP3, SMTP, and all that.
 * Messaging Services::          Messaging services.
@@ -12842,6 +12844,48 @@ bluetooth keyboard or mouse.
 Users need to be in the @code{lp} group to access the D-Bus service.
 @end deffn
 
+@node Sound Services
+@subsubsection Sound Services
+
+@cindex sound support
+@cindex ALSA
+@cindex PulseAudio, sound support
+
+The @code{(gnu services sound)} module provides an
+@code{alsa-service-type} service to generate an ALSA
+@file{/etc/asound.conf} configuration file.  This configuration file is
+what allows applications that produce sound using ALSA to be correctly
+handled.
+
+@deffn {Scheme Variable} alsa-service-type
+This is the type for the @uref{https://alsa-project.org/, ALSA},
+@command{alsa-configuration} record as in this example:
+
+@example
+(service alsa-service-type)
+@end example
+
+See below for details about @code{alsa-configuration}.
+@end deffn
+
+@deftp {Data Type} alsa-configuration
+Data type representing the configuration for @code{alsa-service}.
+
+@table @asis
+@item @code{pulseaudio?} (default: @var{#t})
+Whether ALSA applications should transparently be made to use the
+@uref{http://www.pulseaudio.org/, PulseAudio} sound server.
+
+Using PulseAudio allows you to run several sound-producing applications
+at the same time and to individual control them @i{via}
+@command{pavucontrol}, among other things.
+
+@item @code{extra-options} (default: @var{""})
+String to append to the @file{asound.conf} file.
+
+@end table
+@end deftp
+
 @node Database Services
 @subsubsection Database Services
 

gnu/local.mk

@@ -480,6 +480,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/services/networking.scm			\
   %D%/services/nfs.scm			\
   %D%/services/shepherd.scm			\
+  %D%/services/sound.scm			\
   %D%/services/herd.scm				\
   %D%/services/pm.scm				\
   %D%/services/rsync.scm			\

gnu/services/sound.scm

@@ -0,0 +1,86 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Oleg Pykhalov <go.wigust@gmail.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu services sound)
+  #:use-module (gnu services base)
+  #:use-module (gnu services configuration)
+  #:use-module (gnu services shepherd)
+  #:use-module (gnu services)
+  #:use-module (gnu system shadow)
+  #:use-module (guix gexp)
+  #:use-module (guix packages)
+  #:use-module (guix records)
+  #:use-module (guix store)
+  #:use-module (gnu packages pulseaudio)
+  #:use-module (ice-9 match)
+  #:export (alsa-configuration
+            alsa-service-type))
+
+;;; Commentary:
+;;;
+;;; Sound services.
+;;;
+;;; Code:
+
+
+;;;
+;;; ALSA
+;;;
+
+(define-record-type* <alsa-configuration>
+  alsa-configuration make-alsa-configuration alsa-configuration?
+  (pulseaudio?   alsa-configuration-pulseaudio? ;boolean
+                 (default #t))
+  (extra-options alsa-configuration-extra-options ;string
+                 (default "")))
+
+(define (alsa-config-file config)
+  "Return the ALSA configuration file corresponding to CONFIG."
+  (plain-file "asound.conf"
+              (string-append "# Generated by 'alsa-service'.\n\n"
+                             (if (alsa-configuration-pulseaudio? config)
+                                 "# Use PulseAudio by default
+pcm.!default {
+  type pulse
+  fallback \"sysdefault\"
+  hint {
+    show on
+    description \"Default ALSA Output (currently PulseAudio Sound Server)\"
+  }
+}
+
+ctl.!default {
+  type pulse
+  fallback \"sysdefault\"
+}
+"
+                                 "")
+                             (alsa-configuration-extra-options config))))
+
+(define (alsa-etc-service config)
+  (list `("asound.conf" ,(alsa-config-file config))))
+
+(define alsa-service-type
+  (service-type
+   (name 'alsa)
+   (extensions
+    (list (service-extension etc-service-type alsa-etc-service)))
+   (default-value (alsa-configuration))
+   (description "Configure low-level Linux sound support, ALSA.")))
+
+;;; sound.scm ends here