nixos/scx-loader: init

nixos/doc/manual/release-notes/rl-2611.section.md

@@ -12,6 +12,8 @@
 
 - [tranquil](https://tangled.org/tranquil.farm/tranquil-pds) is an ATProto PDS (personal data server) implementation in Rust. A featureful, spec conscious and community driven alternative to the Bluesky reference implementation PDS. Available as [services.tranquil-pds](#opt-services.tranquil-pds.enable).
 
+- [scx_loader](https://github.com/sched-ext/scx-loader), a system daemon and DBus-based loader for sched_ext schedulers. `scxctl` is the command-line client for interacting with the loader, allowing users to switch schedulers, modes, and arguments dynamically. Available as [services.scx-loader](#opt-services.scx-loader.enable)
+
 - [FlapAlerted](https://github.com/Kioubit/FlapAlerted), detects BGP flapping events and provides statistics based on BGP update messages. Available as [services.flap-alerted](#opt-services.flap-alerted.enable).
 
 ## Backward Incompatibilities {#sec-release-26.11-incompatibilities}

nixos/modules/module-list.nix

@@ -1483,6 +1483,7 @@
   ./services/scheduling/cron.nix
   ./services/scheduling/fcron.nix
   ./services/scheduling/prefect.nix
+  ./services/scheduling/scx-loader.nix
   ./services/scheduling/scx.nix
   ./services/search/elasticsearch-curator.nix
   ./services/search/elasticsearch.nix

nixos/modules/services/scheduling/scx-loader.nix

@@ -0,0 +1,95 @@
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}:
+let
+  cfg = config.services.scx-loader;
+  settingsFormat = pkgs.formats.toml { };
+  configFile = settingsFormat.generate "scx_loader.toml" (
+    lib.filterAttrsRecursive (_: v: v != null) cfg.config
+  );
+
+  schedulers = builtins.concatMap (
+    x: x.passthru.schedulers or (throw "Scheduler not found in package ${x.name}")
+  ) cfg.schedsPackages;
+in
+{
+  options.services.scx-loader = {
+    enable = lib.mkEnableOption "SCX Loader service, a daemon to run schedulers from userspace using dbus. This requires kernel version 6.12 and later.";
+
+    package = lib.mkPackageOption pkgs "scx-loader" { };
+
+    schedsPackages = lib.mkOption {
+      type = lib.types.listOf lib.types.package;
+      default = [ pkgs.scx.rustscheds ];
+      defaultText = lib.literalExpression "[ pkgs.scx.rustscheds ]";
+      example = lib.literalExpression "[ pkgs.scx.full ]";
+      description = ''
+        `scx` package to use. Defaults to `scx.rustscheds`, which includes all currently by `scx_loader` supported schedulers.
+      '';
+    };
+
+    config = lib.mkOption {
+      type = lib.types.submodule {
+        freeformType = settingsFormat.type;
+
+        options = {
+          default_sched = lib.mkOption {
+            type = lib.types.nullOr lib.types.str;
+            default = null;
+            example = "scx_bpfland";
+            description = ''
+              Default scheduler that will be started automatically when `scx_loader` starts.
+              If not set or set to an empty string, `scx_loader` will not start any scheduler by default.
+            '';
+          };
+        };
+      };
+      default = { };
+      description = ''
+        Configuration for `scx_loader`.
+
+        See <https://github.com/sched-ext/scx-loader/blob/main/crates/scx_loader/configuration.md> for the full list of options.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = lib.versionAtLeast config.boot.kernelPackages.kernel.version "6.12";
+        message = "SCX is only supported on kernel version 6.12 and above.";
+      }
+      {
+        assertion = !config.services.scx.enable;
+        message = "services.scx and services.scx_loader cannot be enabled simultaneously. Please enable only one of them.";
+      }
+      {
+        assertion =
+          cfg.config.default_sched == null || lib.elem cfg.config.default_sched ([ "" ] ++ schedulers);
+        message = ''
+          Invalid default scheduler: ${cfg.config.default_sched}. It must be one of: ${lib.concatStringsSep ", " schedulers}.
+        '';
+      }
+    ];
+
+    environment.systemPackages = [ cfg.package ] ++ cfg.schedsPackages;
+    systemd.packages = [ cfg.package ];
+    services.dbus.packages = [ cfg.package ];
+
+    security.polkit.enable = true;
+
+    systemd.services.scx_loader = {
+      path = cfg.schedsPackages;
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig = {
+        TemporaryFileSystem = [ "/etc" ];
+        BindReadOnlyPaths = [ "${configFile.outPath}:/etc/scx_loader.toml" ];
+      };
+    };
+  };
+
+  meta.maintainers = with lib.maintainers; [ ccicnce113424 ];
+}