From 337423af8e63f6d89cfd5818a27e48163239d6bd Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Tue, 19 Jun 2012 17:36:02 -0400
Subject: [PATCH] Backdoor: depend on /dev/hvc0

Systemd is the shit: units can declare a dependency on the appearance
of device nodes.  Yay!
---
 modules/system/boot/systemd.nix          | 21 ++++++++++++++++++++-
 modules/testing/test-instrumentation.nix | 15 +++++----------
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/modules/system/boot/systemd.nix b/modules/system/boot/systemd.nix
index 7fafc94a4bb..6976a204e7f 100644
--- a/modules/system/boot/systemd.nix
+++ b/modules/system/boot/systemd.nix
@@ -12,6 +12,23 @@ let
       description = "Description of this unit used in systemd messages and progress indicators.";
     };
 
+    requires = mkOption {
+      default = [];
+      types = types.listOf types.string;
+      description = ''
+        Start the specified units when this unit is started, and stop
+        this unit when the specified units are stopped or fail.
+      '';
+    };
+
+    wants = mkOption {
+      default = [];
+      types = types.listOf types.string;
+      description = ''
+        Start the specified units when this unit is started.
+      '';
+    };
+
     after = mkOption {
       default = [];
       types = types.listOf types.string;
@@ -33,7 +50,7 @@ let
     wantedBy = mkOption {
       default = [];
       types = types.listOf types.string;
-      description = "Units that want (i.e. depend on) this unit.";
+      description = "Start this unit when the specified units are started.";
     };
 
     environment = mkOption {
@@ -249,6 +266,8 @@ let
           ${optionalString (def.description != "") ''
             Description=${def.description}
           ''}
+          Requires=${concatStringsSep " " def.requires}
+          Wants=${concatStringsSep " " def.wants}
           Before=${concatStringsSep " " def.before}
           After=${concatStringsSep " " def.after}
 
diff --git a/modules/testing/test-instrumentation.nix b/modules/testing/test-instrumentation.nix
index 5e40cf215b7..468a3030ca6 100644
--- a/modules/testing/test-instrumentation.nix
+++ b/modules/testing/test-instrumentation.nix
@@ -21,15 +21,12 @@ in
 
 {
 
-  config =
-  # Require a patch to the kernel to increase the 15s CIFS timeout.
-  mkAssert (config.boot.kernelPackages.kernel.features ? cifsTimeout) "
-    VM tests require that the kernel has the CIFS timeout patch.
-  " {
+  config = {
 
-    jobs.backdoor =
-      { startOn = "started udev";
-        stopOn = "";
+    boot.systemd.services."backdoor.service" =
+      { wantedBy = [ "multi-user.target" ];
+        requires = [ "dev-hvc0.device" ];
+        after = [ "dev-hvc0.device" ];
 
         script =
           ''
@@ -43,8 +40,6 @@ in
             stty -F /dev/hvc0 raw -echo # prevent nl -> cr/nl conversion
             ${pkgs.socat}/bin/socat stdio exec:${rootShell}
           '';
-
-        respawn = false;
       };
 
     boot.initrd.postDeviceCommands =