services: mpd: add more configuration options

* gnu/services/audio.scm (<mpd-configuration>): Add 'db-file', 'state-file'
  and 'sticker-file' fields.
* doc/guix.texi (Music Player Daemon): Document it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -20324,6 +20324,15 @@ The directory to scan for music files.
 @item @code{playlist-dir} (default: @code{"~/.mpd/playlists"})
 The directory to store playlists.
+@item @code{db-file} (default: @code{"~/.mpd/tag_cache"})
+The location of the music database.
+
+@item @code{state-file} (default: @code{"~/.mpd/state"})
+The location of the file that stores current MPD's state.
+
+@item @code{sticker-file} (default: @code{"~/.mpd/sticker.sql"})
+The location of the sticker database.
+
 @item @code{port} (default: @code{"6600"})
 The port to run mpd on.

gnu/services/audio.scm

@@ -42,6 +42,12 @@ (define-record-type* <mpd-configuration>
                 (default "~/Music"))
   (playlist-dir mpd-configuration-playlist-dir
                 (default "~/.mpd/playlists"))
+  (db-file      mpd-configuration-db-file
+                (default "~/.mpd/tag_cache"))
+  (state-file   mpd-configuration-state-file
+                (default "~/.mpd/state"))
+  (sticker-file mpd-configuration-sticker-file
+                (default "~/.mpd/sticker.sql"))
   (port         mpd-configuration-port
                 (default "6600"))
   (address      mpd-configuration-address
@@ -61,6 +67,9 @@ (define (mpd-config->file config)
         `(("user" ,mpd-configuration-user)
           ("music_directory" ,mpd-configuration-music-dir)
           ("playlist_directory" ,mpd-configuration-playlist-dir)
+          ("db_file" ,mpd-configuration-db-file)
+          ("state_file" ,mpd-configuration-state-file)
+          ("sticker_file" ,mpd-configuration-sticker-file)
           ("port" ,mpd-configuration-port)
           ("bind_to_address" ,mpd-configuration-address)))))