nixos/systemd: introduce settingsToSections util, migrate existing rfc42 options to use settingsToSections, migrate oomd to rfc42 (#437477)

nixos/modules/system/boot/systemd.nix

@@ -24,7 +24,7 @@ let
     mountToUnit
     automountToUnit
     sliceToUnit
-    attrsToSection
+    settingsToSections
     ;
 
   upstreamSystemUnits = [
@@ -599,10 +599,7 @@ in
           upstreamWants = upstreamSystemWants;
         };
 
-        "systemd/system.conf".text = ''
-          [Manager]
-          ${attrsToSection cfg.settings.Manager}
-        '';
+        "systemd/system.conf".text = settingsToSections cfg.settings;
 
         "systemd/sleep.conf".text = ''
           [Sleep]

nixos/modules/system/boot/systemd/initrd.nix

@@ -22,7 +22,7 @@ let
     timerToUnit
     mountToUnit
     automountToUnit
-    attrsToSection
+    settingsToSections
     ;
 
   cfg = config.boot.initrd.systemd;
@@ -484,10 +484,7 @@ in
         "/init".source = "${cfg.package}/lib/systemd/systemd";
         "/etc/systemd/system".source = stage1Units;
 
-        "/etc/systemd/system.conf".text = ''
-          [Manager]
-          ${attrsToSection cfg.settings.Manager}
-        '';
+        "/etc/systemd/system.conf".text = settingsToSections cfg.settings;
 
         # We can use either ! or * to lock the root account in the
         # console, but some software like OpenSSH won't even allow you

nixos/modules/system/boot/systemd/logind.nix

@@ -1,7 +1,6 @@
 {
   config,
   lib,
-  pkgs,
   utils,
   ...
 }:
@@ -62,10 +61,8 @@
       "user-runtime-dir@.service"
     ];
 
-    environment.etc."systemd/logind.conf".text = ''
-      [Login]
-      ${utils.systemdUtils.lib.attrsToSection config.services.logind.settings.Login}
-    '';
+    environment.etc."systemd/logind.conf".text =
+      utils.systemdUtils.lib.settingsToSections config.services.logind.settings;
 
     # Restarting systemd-logind breaks X11
     # - upstream commit: https://cgit.freedesktop.org/xorg/xserver/commit/?id=dc48bd653c7e101

nixos/modules/system/boot/systemd/oomd.nix

@@ -1,4 +1,9 @@
-{ config, lib, ... }:
+{
+  config,
+  lib,
+  utils,
+  ...
+}:
 let
 
   cfg = config.systemd.oomd;
@@ -10,6 +15,7 @@ in
       [ "systemd" "oomd" "enableUserServices" ]
       [ "systemd" "oomd" "enableUserSlices" ]
     )
+    (lib.mkRenamedOptionModule [ "systemd" "oomd" "extraConfig" ] [ "systemd" "oomd" "settings" "OOM" ])
   ];
 
   options.systemd.oomd = {
@@ -23,20 +29,18 @@ in
     enableSystemSlice = lib.mkEnableOption "oomd on the system slice (`system.slice`)";
     enableUserSlices = lib.mkEnableOption "oomd on all user slices (`user@.slice`) and all user owned slices";
 
-    extraConfig = lib.mkOption {
-      type =
-        with lib.types;
-        attrsOf (oneOf [
-          str
-          int
-          bool
-        ]);
-      default = { };
-      example = lib.literalExpression ''{ DefaultMemoryPressureDurationSec = "20s"; }'';
+    settings.OOM = lib.mkOption {
       description = ''
-        Extra config options for `systemd-oomd`. See {command}`man oomd.conf`
-        for available options.
+        Settings option for systemd-oomd.
+        See {manpage}`oomd.conf(5)` for available options.
       '';
+      type = lib.types.submodule {
+        freeformType = lib.types.attrsOf utils.systemdUtils.unitOptions.unitOption;
+      };
+      default = { };
+      example = {
+        DefaultMemoryPressureLimit = "60%";
+      };
     };
   };
 
@@ -52,11 +56,7 @@ in
     ];
     systemd.services.systemd-oomd.wantedBy = [ "multi-user.target" ];
 
-    environment.etc."systemd/oomd.conf".text = lib.generators.toINI { } {
-      OOM = cfg.extraConfig;
-    };
-
-    systemd.oomd.extraConfig.DefaultMemoryPressureDurationSec = lib.mkDefault "20s"; # Fedora default
+    environment.etc."systemd/oomd.conf".text = utils.systemdUtils.lib.settingsToSections cfg.settings;
 
     users.users.systemd-oom = {
       description = "systemd-oomd service user";