From 0017a06717bb18706ac3cb99432034caad0c8b91 Mon Sep 17 00:00:00 2001
From: Jan Malakhovski <oxij@oxij.org>
Date: Thu, 18 Apr 2019 10:40:48 +0000
Subject: [PATCH] nixos/systemd: add an option to suppress system units

---
 nixos/modules/system/boot/systemd.nix | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/system/boot/systemd.nix b/nixos/modules/system/boot/systemd.nix
index 18ee2ef1b8f..8118279fcd0 100644
--- a/nixos/modules/system/boot/systemd.nix
+++ b/nixos/modules/system/boot/systemd.nix
@@ -742,6 +742,18 @@ in
       '';
     };
 
+    systemd.suppressedSystemUnits = mkOption {
+      default = [ ];
+      type = types.listOf types.str;
+      example = [ "systemd-backlight@.service" ];
+      description = ''
+        A list of units to suppress when generating system systemd configuration directory. This has
+        priority over upstream units, <option>systemd.units</option>, and
+        <option>systemd.additionalUpstreamSystemUnits</option>. The main purpose of this is to
+        suppress a upstream systemd unit with any modifications made to it by other NixOS modules.
+      '';
+    };
+
   };
 
 
@@ -771,8 +783,11 @@ in
         done;
         ${concatStrings (mapAttrsToList (generator: target: "ln -s ${target} $out/${generator};\n") cfg.generators)}
       '';
+
+      enabledUpstreamSystemUnits = filter (n: ! elem n cfg.suppressedSystemUnits) upstreamSystemUnits;
+      enabledUnits = filterAttrs (n: v: ! elem n cfg.suppressedSystemUnits) cfg.units;
     in ({
-      "systemd/system".source = generateUnits "system" cfg.units upstreamSystemUnits upstreamSystemWants;
+      "systemd/system".source = generateUnits "system" enabledUnits enabledUpstreamSystemUnits upstreamSystemWants;
 
       "systemd/user".source = generateUnits "user" cfg.user.units upstreamUserUnits [];