Subject: [bug#28059] [PATCH] gnu: Add mpd service.

From: Christopher Baines <[email-masked]>
Date: Sat, 12 Aug 2017 21:58:33 +0100

On Sat, 12 Aug 2017 19:10:08 +0200
Peter Mikkelsen <[email-masked]> wrote:

> Hi, thanks for the quick review!
> 
> Christopher Baines <[email-masked]> writes:
> 
> > Hey,
> >
> > This looks great Peter, awesome job :) I've made some notes about
> > potential improvements inline below.
> >
> > I've succeeded in running the system test locally, but there was
> > some suspicious output in the log:
> >
> > exception: bind to '0.0.0.0:6600' failed (continuing anyway, because
> > binding to '[::]:6600' succeeded): Failed to bind socket: Address
> > already in use exception: Failed to access /root/.mpd/playlists: No
> > such file or directory
> >  
> 
> This is pretty normal for mpd, and I believe happens because it first
> binds on IPv6 and then fails for IPv4. The error about the playlist
> dir happens because it does not exist, but AFAIK it is no problem
> unless you want to save playlists. The user can just create the dir.

Ok, good to know :)

> > On Sat, 12 Aug 2017 03:52:11 +0200
> > Peter Mikkelsen <[email-masked]> wrote:  
> >> * doc/guix.text: Add documentation.  
> >
> > Typo above, text rather than texi.
> >  
> 
> Ups, my mistake.
> 
> >> * gnu/services/music.scm (<mpd-configuration>): New record type.
> >>   (mpd-service): New service extension.
> >>   (mpd-service-type): New service type.
> >> * gnu/tests/music.scm: New file.
> >> * gnu/local.mk: Add new files.
> >>
> >> ---
> >>  doc/guix.texi          | 53 +++++++++++++++++++++++++++++++
> >>  gnu/local.mk           |  2 ++
> >>  gnu/services/music.scm | 84
> >> ++++++++++++++++++++++++++++++++++++++++++++++++++
> >> gnu/tests/music.scm    | 83
> >> +++++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed,
> >> 222 insertions(+) create mode 100644 gnu/services/music.scm create
> >> mode 100644 gnu/tests/music.scm
> >>
> >> diff --git a/doc/guix.texi b/doc/guix.texi
> >> index 8f14ddd50..e565dfdc9 100644
> >> --- a/doc/guix.texi
> >> +++ b/doc/guix.texi
> >> @@ -227,6 +227,7 @@ Services
> >>  * Network File System::         NFS related services.
> >>  * Continuous Integration::      The Cuirass service.
> >>  * Power management Services::   The TLP tool.
> >> +* Music Services::              The MPD.
> >>  * Miscellaneous Services::      Other services.
> >>
> >>  Defining Services
> >> @@ -9035,6 +9036,7 @@ declaration.
> >>  * Network File System::         NFS related services.
> >>  * Continuous Integration::      The Cuirass service.
> >>  * Power management Services::   The TLP tool.
> >> +* Music Services::              The MPD.
> >>  * Miscellaneous Services::      Other services.
> >>  @end menu
> >>
> >> @@ -15635,6 +15637,57 @@ Package object of thermald.
> >>  @end table
> >>  @end deftp
> >>
> >> +@node Music Services
> >> +@subsubsection Music Services  
> >
> > I'm wondering if Audio services, rather than Music services might be
> > better? Maybe this would fit in other services related to audio,
> > e.g. Jack, MIDI stuff, etc...
> >  
> 
> That sounds like a good idea.
> 
> >> +@cindex mpd
> >> +@subsubheading Music Player Daemon
> >> +
> >> +The @code{(gnu services music)} provides a service to start MPD
> >> (the Music +Player Daemon). It uses pulseaudio for output.
> >> +
> >> +@defvr {Scheme Variable} mpd-service-type
> >> +The service type for @command{mpd}
> >> +@end defvr
> >> +
> >> +@deftp {Data Type} mpd-configuration
> >> +Data type representing the configuration of @command{mpd}.
> >> +
> >> +@table @asis
> >> +@item @code{user} (default: @code{"mpd"})
> >> +The user to run mpd as.
> >> +
> >> +@item @code{music-dir} (default: @code{"~/Music"})
> >> +The directory to scan for music files.
> >> +
> >> +@item @code{playlist-dir} (default: @code{"~/.mpd/playlists"})
> >> +The directory to store playlists.
> >> +
> >> +@item @code{pid-file} (default: @code{"~/.mpd-pid"})
> >> +The file mpd wil store its PID.
> >> +
> >> +@item @code{port} (default: @code{"6600"})
> >> +The port to run mpd on.
> >> +
> >> +@item @code{address} (default: @code{"any"})
> >> +The address that mpd will bind to. To use a Unix domain socket,
> >> +an absolute path can be specified here.  
> >
> > The style for Guix is to use two spaces between sentences, I always
> > forget about this too.
> >  
> 
> Oh yes, me too.
> 
> >> +
> >> +@end table
> >> +@end deftp
> >> +
> >> +@deffn {Scheme Procedure} mpd-service [#:config
> >> (mpd-configuration)] +Return a service that runs @code{mpd} using
> >> @var{configuration}, +a @code{<mpd-configuration>} object.
> >> +
> >> +The following example shows how one might run @code{mpd} as user
> >> +@code{"bob"} on port @code{6666}.
> >> +@example
> >> +(mpd-service (mpd-configuration
> >> +              (user "bob")
> >> +              (port "6666")))
> >> +@end example
> >> +@end deffn
> >>
> >>  @node Miscellaneous Services
> >>  @subsubsection Miscellaneous Services
> >> diff --git a/gnu/local.mk b/gnu/local.mk
> >> index b1ff72d6a..cad0ba38d 100644
> >> --- a/gnu/local.mk
> >> +++ b/gnu/local.mk
> >> @@ -441,6 +441,7 @@ GNU_SYSTEM_MODULES
> >> =				\
> >> %D%/services/mail.scm				\
> >> %D%/services/mcron.scm			\
> >> %D%/services/messaging.scm			\
> >> +  %D%/services/music.scm                        \
> >>    %D%/services/networking.scm			\
> >>    %D%/services/nfs.scm			\
> >>    %D%/services/shepherd.scm			\
> >> @@ -488,6 +489,7 @@ GNU_SYSTEM_MODULES
> >> =				\
> >> %D%/tests/install.scm				\
> >> %D%/tests/mail.scm				\
> >> %D%/tests/messaging.scm			\
> >> +  %D%/tests/music.scm				\
> >>    %D%/tests/networking.scm			\
> >>    %D%/tests/ssh.scm				\
> >>    %D%/tests/web.scm
> >> diff --git a/gnu/services/music.scm b/gnu/services/music.scm
> >> new file mode 100644
> >> index 000000000..77912d5c6
> >> --- /dev/null
> >> +++ b/gnu/services/music.scm
> >> @@ -0,0 +1,84 @@
> >> +;;; GNU Guix --- Functional package management for GNU
> >> +;;; Copyright © 2017 Peter Mikkelsen <[email-masked]>
> >> +;;;
> >> +;;; 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 music)
> >> +  #:use-module (guix gexp)
> >> +  #:use-module (gnu services)
> >> +  #:use-module (gnu services shepherd)
> >> +  #:use-module (gnu packages mpd)
> >> +  #:use-module (guix records)
> >> +  #:export (mpd-configuration
> >> +            mpd-configuration?
> >> +            mpd-service
> >> +            mpd-service-type))
> >> +
> >> +;;; Commentary:
> >> +;;;
> >> +;;; Music related services
> >> +;;;
> >> +;;; Code:
> >> +
> >> +(define-record-type* <mpd-configuration>
> >> +  mpd-configuration make-mpd-configuration
> >> +  mpd-configuration?
> >> +  (user         mpd-configuration-user
> >> +                (default "mpd"))
> >> +  (music-dir    mpd-configuration-music-dir
> >> +                (default "~/Music"))
> >> +  (playlist-dir mpd-configuration-playlist-dir
> >> +                (default "~/.mpd/playlists"))
> >> +  (port         mpd-configuration-port
> >> +                (default "6600"))
> >> +  (address      mpd-configuration-address
> >> +                (default "any"))
> >> +  (pid-file     mpd-configuration-pid-file
> >> +                (default "~/.mpd-pid")))
> >> +
> >> +(define (mpd-config->file config)
> >> +  (apply
> >> +   mixed-text-file "mpd.conf"
> >> +   "audio_output {\n"
> >> +   "  type \"pulse\"\n"
> >> +   "  name \"MPD\"\n"
> >> +   "}\n"
> >> +   (map (lambda (config-line)
> >> +          (let ((config-name (car config-line))
> >> +                (config-val (cadr config-line)))
> >> +            (string-append config-name " \"" (config-val config)
> >> "\"\n")))
> >> +        `(("user" ,mpd-configuration-user)
> >> +          ("music_directory" ,mpd-configuration-music-dir)
> >> +          ("playlist_directory" ,mpd-configuration-playlist-dir)
> >> +          ("port" ,mpd-configuration-port)
> >> +          ("bind_to_address" ,mpd-configuration-address)
> >> +          ("pid_file" ,mpd-configuration-pid-file)))))
> >> +
> >> +(define mpd-service-type
> >> +  (shepherd-service-type
> >> +   'mpd
> >> +   (lambda (config)
> >> +     (shepherd-service
> >> +      (documentation "Run the MPD (Music Player Daemon)")
> >> +      (provision '(mpd))
> >> +      (start #~(make-forkexec-constructor
> >> +                (list #$(file-append mpd "/bin/mpd")
> >> +                      "--no-daemon"
> >> +                      #$(mpd-config->file config))))
> >> +      (stop  #~(make-kill-destructor))))))
> >> +
> >> +(define* (mpd-service #:optional (config (mpd-configuration)))
> >> +  (service mpd-service-type config))  
> >
> > I've been trying a slightly different style for this recently. At
> > the moment, if you had a configuration file for MPD, you couldn't
> > use this with the service here. One way of addressing this is to do
> > something like the Tailon service, and define a gexp compiler for
> > the configuration file (e.g. [1]). For the Tailon service, this
> > means that you should be able to pass your own configuration file
> > to the service. 
> 
> I am not sure I get how this works, and I would probs just make a big
> mess. What about we take my approach first, and then I can come back
> to it when I learn some more about guix?

No problem. Looking at it again, I think it might be a bit trickier
than I initially assumed, as the pid-file value is used.

> > Also, now that a <service-type> can have a default-value, I think
> > its easier to just have the mpd-service-type, without the
> > mpd-service procedure. If you add a default value, you should be
> > able to do (service mpd-service-type).
> >  
> Ok with me.
> 
> > 1:
> > https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/admin.scm#n255
> >  
> >> diff --git a/gnu/tests/music.scm b/gnu/tests/music.scm
> >> new file mode 100644
> >> index 000000000..158513098
> >> --- /dev/null
> >> +++ b/gnu/tests/music.scm
> >> @@ -0,0 +1,83 @@
> >> +;;; GNU Guix --- Functional package management for GNU
> >> +;;; Copyright © 2017 Peter Mikkelsen <[email-masked]>
> >> +;;;
> >> +;;; 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 tests music)
> >> +  #:use-module (gnu tests)
> >> +  #:use-module (gnu system)
> >> +  #:use-module (gnu system vm)
> >> +  #:use-module (gnu services)
> >> +  #:use-module (gnu services music)
> >> +  #:use-module (gnu packages mpd)
> >> +  #:use-module (guix gexp)
> >> +  #:export (%test-mpd))
> >> +
> >> +(define %mpd-os
> >> +  (simple-operating-system
> >> +   (mpd-service (mpd-configuration
> >> +                 (user "root")))))
> >> +
> >> +(define (run-mpd-test)
> >> +  "Run tests in %mpd-os, which has mpd running."
> >> +  (define os
> >> +    (marionette-operating-system
> >> +     %mpd-os
> >> +     #:imported-modules '((gnu services herd))))
> >> +
> >> +  (define vm
> >> +    (virtual-machine os))
> >> +
> >> +  (define test
> >> +    (with-imported-modules '((gnu build marionette))
> >> +      #~(begin
> >> +          (use-modules (srfi srfi-64)
> >> +                       (gnu build marionette))
> >> +          (define marionette
> >> +            (make-marionette (list #$vm)))
> >> +
> >> +          (mkdir #$output)
> >> +          (chdir #$output)
> >> +
> >> +          (test-begin "mpd")
> >> +
> >> +          (test-eq "service is running"
> >> +            'running!
> >> +            (marionette-eval
> >> +             '(begin
> >> +                (use-modules (gnu services herd))
> >> +                (start-service 'mpd)
> >> +                'running!)
> >> +             marionette))  
> >
> > Recently, the start-service procedure was changed to return the
> > information from the shepherd, and this can be used to make this
> > check a bit more rigorous.
> >
> > I've got an patch for the Memcached service which demonstrates this
> > here [2], as with the test above, it will not always fail, even if
> > the service fails to create the PID file.
> >
> > 2: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=28021
> >  
> >> +          (test-assert "pid file"
> >> +            (wait-for-file "/root/.mpd-pid"
> >> +             marionette))  
> >
> > If this is useful when using MPD, then I think it would be valuable
> > to get the shepherd to wait for the PID file. I think you can do
> > this by adding #:pid-file to the make-forkexec-constructor call.
> >
> > If you do this, them I'm not sure this test adds anything, as I
> > think the start-service call would only return successfully when
> > the service has started, and created the PID file.
> >  
> 
> Right, I have removed this test.

Great. Just to check I wasn't wrong, I've just tested what happens if
you break the service by getting mpd to create the PID file, and
shepherd to look for it in different places, and the previous test
about starting the service does indeed fail, which is what we want :D

> >> +          (test-assert "mpc connect"
> >> +            (marionette-eval
> >> +             '(zero? (system #$(file-append mpd-mpc "/bin/mpc")))
> >> +             marionette))
> >> +
> >> +          (test-end)
> >> +          (exit (= (test-runner-fail-count (test-runner-current))
> >> 0)))))
> >> +  (gexp->derivation "mpd-test" test))
> >> +
> >> +(define %test-mpd
> >> +  (system-test
> >> +   (name "mpd")
> >> +   (description "Test that the mpd can run and be connected to.")
> >> +   (value (run-mpd-test))))  
> 
> I think I have fixed all of your suggestions (apart from the
> gexp-compiler one). Please see my new patch.

Awesome, I've put a couple more suggestions below, but just on the docs
and a bit of code style. Regardless of these, I think this is good to
go.

> From 419a8df59bc958ee87ece5519393b32cfbef609c Mon Sep 17 00:00:00 2001
> From: Peter Mikkelsen <[email-masked]>
> Date: Sat, 12 Aug 2017 03:40:25 +0200
> Subject: [PATCH] gnu: Add mpd service.
> 
> * doc/guix.texi: Add documentation.
> * gnu/services/audio.scm (<mpd-configuration>): New record type.
>   (mpd-service-type): New service type.
> * gnu/tests/audio.scm: New file.
> * gnu/local.mk: Add new files.
> ---
>  doc/guix.texi          | 49 ++++++++++++++++++++++++++++
>  gnu/local.mk           |  2 ++
>  gnu/services/audio.scm | 86
> ++++++++++++++++++++++++++++++++++++++++++++++++++
> gnu/tests/audio.scm    | 78
> +++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 215
> insertions(+) create mode 100644 gnu/services/audio.scm create mode
> 100644 gnu/tests/audio.scm
> 
> diff --git a/doc/guix.texi b/doc/guix.texi
> index 8f14ddd50..754408ade 100644
> --- a/doc/guix.texi
> +++ b/doc/guix.texi
> @@ -227,6 +227,7 @@ Services
>  * Network File System::         NFS related services.
>  * Continuous Integration::      The Cuirass service.
>  * Power management Services::   The TLP tool.
> +* Audio Services::              The MPD.
>  * Miscellaneous Services::      Other services.
>  
>  Defining Services
> @@ -9035,6 +9036,7 @@ declaration.
>  * Network File System::         NFS related services.
>  * Continuous Integration::      The Cuirass service.
>  * Power management Services::   The TLP tool.
> +* Audio Services::              The MPD.
>  * Miscellaneous Services::      Other services.
>  @end menu
>  
> @@ -15635,6 +15637,53 @@ Package object of thermald.
>  @end table
>  @end deftp
>  
> +@node Audio Services
> +@subsubsection Audio Services
> +
> +@cindex mpd
> +@subsubheading Music Player Daemon
> +
> +The @code{(gnu services audio)} provides a service to start MPD (the
> Music +Player Daemon).  It uses pulseaudio for output.
> +
> +@defvr {Scheme Variable} mpd-service-type
> +The service type for @command{mpd}
> +@end defvr
> +
> +@deftp {Data Type} mpd-configuration
> +Data type representing the configuration of @command{mpd}.
> +
> +@table @asis
> +@item @code{user} (default: @code{"mpd"})
> +The user to run mpd as.
> +
> +@item @code{music-dir} (default: @code{"~/Music"})
> +The directory to scan for music files.
> +
> +@item @code{playlist-dir} (default: @code{"~/.mpd/playlists"})
> +The directory to store playlists.
> +
> +@item @code{pid-file} (default: @code{"/var/run/mpd.pid"})
> +The file mpd wil store its PID.  This must be an absolute path.
> +
> +@item @code{port} (default: @code{"6600"})
> +The port to run mpd on.
> +
> +@item @code{address} (default: @code{"any"})
> +The address that mpd will bind to.  To use a Unix domain socket,
> +an absolute path can be specified here.
> +
> +@end table
> +@end deftp
> +
> +The following example shows how one might run @code{mpd} as user
> +@code{"bob"} on port @code{6666}.
> +@example
> +(service mpd-service-type
> +         (mpd-configuration
> +          (user "bob")
> +          (port "6666")))
> +@end example

I've got a few suggestions for the docs. Nothing too important, and I'm
fine if you still prefer docs without the suggestions below, but feel
free to pick and choose any changes that you think are good, I've put
my reasoning inline in round brackets.

@node Audio Services
@subsubsection Audio Services

The @code{(gnu services audio)} module provides a service to
start MPD (the Music Player Daemon).  

  (
  Having the introduction to the module above the Music Player Daemon
  subsubheading seems neater. Also, I think adding "module" after
  @code{(gnu services audio)} helps with readability.
  )

@cindex mpd
@subsubheading Music Player Daemon

The Music Player Daemon (MPD) is a service that can play music while
being controlled from the local machine or over the network by a
variety of clients.

  (
  An introductory paragraph about what the service does might be
  useful, so I've written one above.
  )

The following example shows how one might run @code{mpd} as user
@code{"bob"} on port @code{6666}.  It uses pulseaudio for output.

@example
(service mpd-service-type
         (mpd-configuration
          (user "bob")
          (port "6666")))
@end example

  (
  Moving the example here might be more visible, rather than below the
  reference documentation.
  )

@defvr {Scheme Variable} mpd-service-type
The service type for @command{mpd}
@end defvr

@deftp {Data Type} mpd-configuration
Data type representing the configuration of @command{mpd}.

...

@end table
@end deftp

>  @node Miscellaneous Services
>  @subsubsection Miscellaneous Services
> diff --git a/gnu/local.mk b/gnu/local.mk
> index cffb18d3a..c12fd8559 100644
> --- a/gnu/local.mk
> +++ b/gnu/local.mk
> @@ -426,6 +426,7 @@ GNU_SYSTEM_MODULES
> =				\ \
>    %D%/services.scm				\
>    %D%/services/admin.scm			\
> +  %D%/services/audio.scm                        \
>    %D%/services/avahi.scm			\
>    %D%/services/base.scm				\
>    %D%/services/configuration.scm		\
> @@ -481,6 +482,7 @@ GNU_SYSTEM_MODULES
> =				\ \
>    %D%/tests.scm					\
>    %D%/tests/admin.scm				\
> +  %D%/tests/audio.scm				\
>    %D%/tests/base.scm				\
>    %D%/tests/databases.scm			\
>    %D%/tests/dict.scm				\
> diff --git a/gnu/services/audio.scm b/gnu/services/audio.scm
> new file mode 100644
> index 000000000..f5c465341
> --- /dev/null
> +++ b/gnu/services/audio.scm
> @@ -0,0 +1,86 @@
> +;;; GNU Guix --- Functional package management for GNU
> +;;; Copyright © 2017 Peter Mikkelsen <[email-masked]>
> +;;;
> +;;; 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 audio)
> +  #:use-module (guix gexp)
> +  #:use-module (gnu services)
> +  #:use-module (gnu services shepherd)
> +  #:use-module (gnu packages mpd)
> +  #:use-module (guix records)
> +  #:export (mpd-configuration
> +            mpd-configuration?
> +            mpd-service-type))
> +
> +;;; Commentary:
> +;;;
> +;;; Audio related services
> +;;;
> +;;; Code:
> +
> +(define-record-type* <mpd-configuration>
> +  mpd-configuration make-mpd-configuration
> +  mpd-configuration?
> +  (user         mpd-configuration-user
> +                (default "mpd"))
> +  (music-dir    mpd-configuration-music-dir
> +                (default "~/Music"))
> +  (playlist-dir mpd-configuration-playlist-dir
> +                (default "~/.mpd/playlists"))
> +  (port         mpd-configuration-port
> +                (default "6600"))
> +  (address      mpd-configuration-address
> +                (default "any"))
> +  (pid-file     mpd-configuration-pid-file
> +                (default "/var/run/mpd.pid")))
> +
> +(define (mpd-config->file config)
> +  (apply
> +   mixed-text-file "mpd.conf"
> +   "audio_output {\n"
> +   "  type \"pulse\"\n"
> +   "  name \"MPD\"\n"
> +   "}\n"
> +   (map (lambda (config-line)
> +          (let ((config-name (car config-line))
> +                (config-val (cadr config-line)))
> +            (string-append config-name " \"" (config-val config)
> "\"\n")))

One way of making this a bit more concise and remove the need for car
and cadr is to use the match module (ice-9 match).

   (map (match-lambda
         ((config-name config-val)
          (string-append config-name " \"" (config-val config) "\"\n")))
        ...

> +        `(("user" ,mpd-configuration-user)
> +          ("music_directory" ,mpd-configuration-music-dir)
> +          ("playlist_directory" ,mpd-configuration-playlist-dir)
> +          ("port" ,mpd-configuration-port)
> +          ("bind_to_address" ,mpd-configuration-address)
> +          ("pid_file" ,mpd-configuration-pid-file)))))
> +

...