nixos/alsa: add bluetooth support (#475100)

nixos/doc/manual/release-notes/rl-2605.section.md

@@ -128,6 +128,8 @@ See <https://github.com/NixOS/nixpkgs/issues/481673>.
 
 - [services.resolved](#opt-services.resolved.enable) module was converted to RFC42-style settings. The moved options have also been renamed to match the upstream names. Aliases mean current configs will continue to function, but users should move to the new options as convenient.
 
+- Support for Bluetooth audio based on `bluez-alsa` has been added to the `hardware.alsa` module. It can be enabled with the new [enableBluetooth](#opt-hardware.alsa.enableBluetooth) option.
+
 - `services.openssh` now supports generating host SSH keys by setting `services.openssh.generateHostKeys = true` while leaving `services.openssh.enable` disabled.  This is particularly useful for systems that have no need of an SSH daemon but want SSH host keys for other purposes such as using agenix or sops-nix.
 
 - `services.slurm` now supports slurmrestd usage through the `services.slurm.rest` NixOS options.

nixos/modules/services/audio/alsa.nix

@@ -44,9 +44,15 @@ let
     in
     lib.forEach options (i: "options ${i.driver} index=${toList i.ids} id=${toList i.names}");
 
-  defaultDeviceVars = {
+  pluginsPath = pkgs.symlinkJoin {
+    name = "alsa-with-plugins";
+    paths = cfg.plugins;
+  };
+
+  alsaVariables = {
     "ALSA_AUDIO_OUT" = cfg.defaultDevice.playback;
     "ALSA_AUDIO_IN" = cfg.defaultDevice.capture;
+    "ALSA_PLUGIN_DIR" = lib.mkIf (cfg.plugins != [ ]) "${pluginsPath}/lib/alsa-lib";
   };
 
 in
@@ -106,6 +112,8 @@ in
 
     enableOSSEmulation = lib.mkEnableOption "the OSS emulation";
 
+    enableBluetooth = lib.mkEnableOption "Bluetooth audio support via BlueALSA";
+
     enableRecorder = lib.mkOption {
       type = lib.types.bool;
       default = false;
@@ -125,6 +133,15 @@ in
       '';
     };
 
+    plugins = lib.mkOption {
+      type = lib.types.listOf lib.types.package;
+      default = [ ];
+      example = lib.literalExpression "[ pkgs.bluez-alsa ]";
+      description = ''
+        List of ALSA plugins to be added to the search path.
+      '';
+    };
+
     defaultDevice.playback = lib.mkOption {
       type = lib.types.str;
       default = "";
@@ -392,8 +409,8 @@ in
       };
 
       # Set default PCM devices
-      environment.sessionVariables = defaultDeviceVars;
-      systemd.globalEnvironment = defaultDeviceVars;
+      environment.sessionVariables = alsaVariables;
+      systemd.globalEnvironment = alsaVariables;
 
       environment.etc."asound.conf".text = cfg.config;
 
@@ -412,6 +429,33 @@ in
       environment.systemPackages = [ pkgs.alsa-utils ];
     })
 
+    (lib.mkIf (cfg.enable && cfg.enableBluetooth) {
+
+      users.users.bluealsa = {
+        description = "BlueALSA daemons user";
+        isSystemUser = true;
+        group = "audio";
+      };
+
+      # Link ALSA configuration
+      environment.etc."alsa/conf.d/20-bluealsa.conf".source =
+        "${pkgs.bluez-alsa}/etc/alsa/conf.d/20-bluealsa.conf";
+
+      # Install plugin
+      hardware.alsa.plugins = [ pkgs.bluez-alsa ];
+
+      # Install CLI tools and systemd units
+      environment.systemPackages = [ pkgs.bluez-alsa ];
+      systemd.packages = [ pkgs.bluez-alsa ];
+
+      # See Nixpkgs issue #81138
+      systemd.services."bluealsa".wantedBy = [ "bluetooth.target" ];
+
+      # Note: bluealsa-aplay is available but we don't start it
+      # by default, it's only needed to make the machine act as
+      # bluetooth speaker
+    })
+
     (lib.mkIf config.hardware.alsa.enablePersistence {
 
       # Install udev rules for restoring card settings on boot

pkgs/by-name/bl/bluez-alsa/package.nix

@@ -16,6 +16,8 @@
   readline,
   sbc,
   python3,
+  systemdSupport ? true,
+  systemdLibs,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -37,7 +39,8 @@ stdenv.mkDerivation (finalAttrs: {
     autoreconfHook
     pkg-config
     python3
-  ];
+  ]
+  ++ lib.optional systemdSupport systemdLibs;
 
   buildInputs = [
     alsa-lib
@@ -49,9 +52,7 @@ stdenv.mkDerivation (finalAttrs: {
     libbsd
     ncurses
   ]
-  ++ lib.optionals aacSupport [
-    fdk_aac
-  ];
+  ++ lib.optional aacSupport fdk_aac;
 
   configureFlags = [
     (lib.enableFeature aacSupport "aac")
@@ -59,6 +60,10 @@ stdenv.mkDerivation (finalAttrs: {
     (lib.enableFeature true "rfcomm")
     (lib.withFeatureAs true "alsaplugindir" "${placeholder "out"}/lib/alsa-lib")
     (lib.withFeatureAs true "dbusconfdir" "${placeholder "out"}/share/dbus-1/system.d")
+    (lib.enableFeature systemdSupport "systemd")
+    (lib.withFeatureAs systemdSupport "systemdsystemunitdir" "${placeholder "out"}/lib/systemd/system")
+    (lib.withFeatureAs systemdSupport "bluealsauser" "bluealsa")
+    (lib.withFeatureAs systemdSupport "bluealsaaplayuser" "bluealsa")
   ];
 
   passthru.updateScript = gitUpdater { };