nixos/monado: add forceDefaultRuntime optionorigin/backport-348815-to-release-24.11

This option replaces the active runtime manifest in the user directory.
Games running through Steam's Pressure Vessel cannot read /etc so
forcefully overriding the file every time the service starts, will allow
those games to use Monado.

Signed-off-by: Sefa Eyeoglu <contact@scrumplex.net>
(cherry picked from commit 91fee431005a26e238ecc6ed273eb3d413b0add6)

2 files changed, 34 insertions, 2 deletions

diff --git a/nixos/modules/services/hardware/monado.nix b/nixos/modules/services/hardware/monado.nix
index f7fdf421ac17..137b63c77420 100644
--- a/nixos/modules/services/hardware/monado.nix
+++ b/nixos/modules/services/hardware/monado.nix
@@ -16,6 +16,7 @@ let
 
   cfg = config.services.monado;
 
+  runtimeManifest = "${cfg.package}/share/openxr/1/openxr_monado.json";
 in
 {
   options.services.monado = {
@@ -35,6 +36,19 @@ in
       example = true;
     };
 
+    forceDefaultRuntime = mkOption {
+      type = types.bool;
+      description = ''
+        Whether to ensure that Monado is the active runtime set for the current
+        user.
+
+        This replaces the file `XDG_CONFIG_HOME/openxr/1/active_runtime.json`
+        when starting the service.
+      '';
+      default = false;
+      example = true;
+    };
+
     highPriority =
       mkEnableOption "high priority capability for monado-service"
       // mkOption { default = true; };
@@ -68,6 +82,16 @@ in
           IPC_EXIT_ON_DISCONNECT = mkDefault "off";
         };
 
+        preStart = mkIf cfg.forceDefaultRuntime ''
+          XDG_CONFIG_HOME="''${XDG_CONFIG_HOME:-$HOME/.config}"
+          targetDir="$XDG_CONFIG_HOME/openxr/1"
+          activeRuntimePath="$targetDir/active_runtime.json"
+
+          echo "Note: Replacing active runtime at '$activeRuntimePath'"
+          mkdir --parents "$targetDir"
+          ln --symbolic --force ${runtimeManifest} "$activeRuntimePath"
+        '';
+
         serviceConfig = {
           ExecStart =
             if cfg.highPriority then
@@ -106,7 +130,7 @@ in
     hardware.graphics.extraPackages = [ pkgs.monado-vulkan-layers ];
 
     environment.etc."xdg/openxr/1/active_runtime.json" = mkIf cfg.defaultRuntime {
-      source = "${cfg.package}/share/openxr/1/openxr_monado.json";
+      source = runtimeManifest;
     };
   };
 
diff --git a/nixos/tests/monado.nix b/nixos/tests/monado.nix
index 2fb94468a2bb..9b7e636d1f66 100644
--- a/nixos/tests/monado.nix
+++ b/nixos/tests/monado.nix
@@ -1,5 +1,5 @@
 import ./make-test-python.nix (
-  { pkgs, ... }:
+  { ... }:
   {
     name = "monado";
 
@@ -16,6 +16,8 @@ import ./make-test-python.nix (
         services.monado = {
           enable = true;
           defaultRuntime = true;
+
+          forceDefaultRuntime = true;
         };
         # Stop Monado from probing for any hardware
         systemd.user.services.monado.environment.SIMULATED_ENABLE = "1";
@@ -30,6 +32,9 @@ import ./make-test-python.nix (
         runtimePath = "/run/user/${userId}";
       in
       ''
+        # for defaultRuntime
+        machine.succeed("stat /etc/xdg/openxr/1/active_runtime.json")
+
         machine.succeed("loginctl enable-linger alice")
         machine.wait_for_unit("user@${userId}.service")
 
@@ -37,6 +42,9 @@ import ./make-test-python.nix (
         machine.systemctl("start monado.service", "alice")
         machine.wait_for_unit("monado.service", "alice")
 
+        # for forceDefaultRuntime
+        machine.succeed("stat /home/alice/.config/openxr/1/active_runtime.json")
+
         machine.succeed("su -- alice -c env XDG_RUNTIME_DIR=${runtimePath} openxr_runtime_list")
       '';
   }