1 files changed, 72 insertions, 0 deletions
diff --git a/nixos/modules/misc/label.nix b/nixos/modules/misc/label.nix
new file mode 100644
index 00000000000..02b91555b3c
--- /dev/null
+++ b/nixos/modules/misc/label.nix
@@ -0,0 +1,72 @@
+{ config, lib, ... }:
+
+with lib;
+
+let
+  cfg = config.system.nixos;
+in
+
+{
+
+  options.system = {
+
+    nixos.label = mkOption {
+      type = types.str;
+      description = ''
+        NixOS version name to be used in the names of generated
+        outputs and boot labels.
+
+        If you ever wanted to influence the labels in your GRUB menu,
+        this is the option for you.
+
+        The default is <option>system.nixos.tags</option> separated by
+        "-" + "-" + <envar>NIXOS_LABEL_VERSION</envar> environment
+        variable (defaults to the value of
+        <option>system.nixos.version</option>).
+
+        Can be overriden by setting <envar>NIXOS_LABEL</envar>.
+
+        Useful for not loosing track of configurations built from different
+        nixos branches/revisions, e.g.:
+
+        <screen>
+        #!/bin/sh
+        today=`date +%Y%m%d`
+        branch=`(cd nixpkgs ; git branch 2>/dev/null | sed -n '/^\* / { s|^\* ||; p; }')`
+        revision=`(cd nixpkgs ; git rev-parse HEAD)`
+        export NIXOS_LABEL_VERSION="$today.$branch-''${revision:0:7}"
+        nixos-rebuild switch</screen>
+      '';
+    };
+
+    nixos.tags = mkOption {
+      type = types.listOf types.str;
+      default = [];
+      example = [ "with-xen" ];
+      description = ''
+        Strings to prefix to the default
+        <option>system.nixos.label</option>.
+
+        Useful for not loosing track of configurations built with
+        different options, e.g.:
+
+        <screen>
+        {
+          system.nixos.tags = [ "with-xen" ];
+          virtualisation.xen.enable = true;
+        }
+        </screen>
+      '';
+    };
+
+  };
+
+  config = {
+    # This is set here rather than up there so that changing it would
+    # not rebuild the manual
+    system.nixos.label = mkDefault (maybeEnv "NIXOS_LABEL"
+                                             (concatStringsSep "-" ((sort (x: y: x < y) cfg.tags)
+                                              ++ [ (maybeEnv "NIXOS_LABEL_VERSION" cfg.version) ])));
+  };
+
+}