Add mpd module

There is room for improvement here. The options in conffile could be broken out into individual options and an extraConfig option added. But I think this looks right.
Patch by mornfall, slightly modified by me

svn path=/nixos/trunk/; revision=30731

modules/misc/ids.nix

@@ -68,6 +68,7 @@ in
     dovenull2 = 47;
     unbound = 48;
     prayer = 49;
+    mpd = 50;
 
     # When adding a uid, make sure it doesn't match an existing gid.
 
@@ -116,6 +117,7 @@ in
     virtuoso = 44;
     dovecot2 = 45;
     prayer = 46;
+    mpd = 47;
 
     # When adding a gid, make sure it doesn't match an existing uid.
 

modules/module-list.nix

@@ -53,6 +53,7 @@
   ./services/audio/alsa.nix
   ./services/audio/fuppes.nix
   ./services/audio/pulseaudio.nix
+  ./services/audio/mpd.nix
   ./services/backup/mysql-backup.nix
   ./services/backup/postgresql-backup.nix
   ./services/backup/sitecopy-backup.nix

modules/services/audio/mpd.nix

@@ -0,0 +1,99 @@
+{ config, pkgs, ... }:
+
+with pkgs.lib;
+
+let
+
+  uid = config.ids.uids.mpd;
+  gid = config.ids.gids.mpd;
+
+in
+
+{
+
+  ###### interface
+
+  options = {
+
+    services.mpd = {
+
+      enable = mkOption {
+        default = false;
+        description = ''
+          Whether to enable the MPD music player daemon (server).
+        '';
+      };
+
+      conffile = mkOption {
+        default = ''
+          music_directory     "${config.services.mpd.dataDir}/music"
+          playlist_directory  "${config.services.mpd.dataDir}/playlists"
+          db_file             "${config.services.mpd.dataDir}/tag_cache"
+          state_file          "${config.services.mpd.dataDir}/state"
+          sticker_file        "${config.services.mpd.dataDir}/sticker.sql"
+          log_file            "/var/log/mpd.log"
+          pid_file            "/var/run/mpd/mpd.pid"
+          bind_to_address     "localhost"
+          user                "mpd"
+        '';
+        description = ''The contents of the MPD configuration file mpd.conf'';
+      };
+
+      dataDir = mkOption {
+        default = "/var/lib/mpd/";
+        example = "debug";
+        description = ''
+          The root directory of the MPD data tree. Contains a tag cache,
+	  playlists and a music/ subdirectory that should contain (or
+          symlink to) your music collection.
+        '';
+      };
+
+    };
+
+  };
+
+
+  ###### implementation
+
+  config = mkIf config.services.mpd.enable {
+
+    environment.systemPackages = [ pkgs.mpd ];
+
+    users.extraUsers = singleton
+      { name = "mpd";
+        group = "mpd";
+        extraGroups = [ "audio" ];
+        description = "MPD system-wide daemon";
+        home = "${config.services.mpd.dataDir}";
+      };
+
+    users.extraGroups = singleton
+      { name = "mpd";
+        inherit gid;
+      };
+
+    jobs.mpd =
+      { description = "MPD system-wide server";
+
+        startOn = "startup";
+
+        preStart =
+          ''
+            mkdir -p /var/run/mpd && chown mpd /var/run/mpd
+            test -d ${config.services.mpd.dataDir} || \
+            ( mkdir -p --mode 755 ${config.services.mpd.dataDir}/music \
+                                  ${config.services.mpd.dataDir}/playlists && \
+              chown -R mpd:mpd ${config.services.mpd.dataDir} )
+          '';
+
+        daemonType = "fork";
+        exec =
+          ''
+            ${pkgs.mpd}/bin/mpd ${pkgs.writeText "mpd.conf" config.services.mpd.conffile}
+          '';
+      };
+
+  };
+
+}