Added configuration.nix option to add entries into nix.conf .

svn path=/nixos/trunk/; revision=8910

system/activate-configuration.sh

@@ -96,6 +96,9 @@ if test -z "@readOnlyRoot@"; then
 # WARNING: this file is generated.
 build-users-group = nixbld
 build-max-jobs = @maxJobs@
+
+@extraNixOptions@
+
 EOF
 
     chown root.nixbld /nix/store

system/options.nix

@@ -847,6 +847,17 @@
     ";
   }
 
+  {
+    name = ["nix" "extraOptions"];
+    default = "";
+    example = "
+	gc-keep-outputs = true
+	gc-keep-derivations = true
+    ";
+    description = "
+	This option allows to append lines to nix.conf. 
+    ";
+  }
   
   {
     name = ["security" "setuidPrograms"];

system/system.nix

@@ -249,6 +249,7 @@ rec {
       config.get ["security" "setuidPrograms"] ++
       config.get ["security" "extraSetuidPrograms"];
     maxJobs = config.get ["nix" "maxJobs"];
+    extraNixOptions = config.get ["nix" "extraOptions"];
 
     inherit (usersGroups) createUsersGroups usersList groupsList;