From b606165bd9d4c8a1f82160f67bd541f064ed1ddc Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Thu, 11 Oct 2012 17:54:43 -0400
Subject: [PATCH] Allow a unit to declare "triggers" that force a restart
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The triggers are just arbitrary strings that are included in the unit
under X-Restart-Triggers.  The idea is that if they change between
reconfigurations, switch-to-configuration will restart the unit
because its store path changed.  This is mostly useful for services
that implicitly depend on generated files in /etc.  Thus you can say

  restartTriggers = [ confFile ];

where ‘confFile’ is the derivation that generated the /etc file in
question.
---
 modules/system/boot/systemd-unit-options.nix | 9 +++++++++
 modules/system/boot/systemd.nix              | 1 +
 2 files changed, 10 insertions(+)

diff --git a/modules/system/boot/systemd-unit-options.nix b/modules/system/boot/systemd-unit-options.nix
index 2efea2fb9e1..239c837c676 100644
--- a/modules/system/boot/systemd-unit-options.nix
+++ b/modules/system/boot/systemd-unit-options.nix
@@ -83,6 +83,15 @@ rec {
       '';
     };
 
+    restartTriggers = mkOption {
+      default = [];
+      description = ''
+        An arbitrary list of items such as derivations.  If any item
+        in the list changes between reconfigurations, the service will
+        be restarted.
+      '';
+    };
+
   };
 
 
diff --git a/modules/system/boot/systemd.nix b/modules/system/boot/systemd.nix
index c166c1cbf03..d88ac652ae0 100644
--- a/modules/system/boot/systemd.nix
+++ b/modules/system/boot/systemd.nix
@@ -176,6 +176,7 @@ let
           Before = concatStringsSep " " config.before;
           BindsTo = concatStringsSep " " config.bindsTo;
           PartOf = concatStringsSep " " config.partOf;
+          "X-Restart-Triggers" = toString config.restartTriggers;
         } // optionalAttrs (config.description != "") {
           Description = config.description;
         };