generalized module for write-text

- use custom etc activation script

3 files changed, 182 insertions, 0 deletions

diff --git a/modules/system/activation-scripts.nix b/modules/system/activation-scripts.nix
new file mode 100644
index 0000000..1efe201
--- /dev/null
+++ b/modules/system/activation-scripts.nix
@@ -0,0 +1,63 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.system;
+
+  script = import ./write-text.nix {
+    inherit lib;
+    mkTextDerivation = name: text: pkgs.writeScript "activate-${name}" text;
+  };
+
+in
+
+{
+  options = {
+
+    system.activationScripts = mkOption {
+      internal = true;
+      type = types.attrsOf (types.submodule script);
+      default = {};
+      description = ''
+        A set of shell script fragments that are executed when a NixOS
+        system configuration is activated.  Examples are updating
+        /etc, creating accounts, and so on.  Since these are executed
+        every time you boot the system or run
+        <command>nixos-rebuild</command>, it's important that they are
+        idempotent and fast.
+      '';
+    };
+
+  };
+
+  config = {
+
+    system.activationScripts.script.text = ''
+      #! ${pkgs.stdenv.shell}
+
+      systemConfig=@out@
+
+      _status=0
+      trap "_status=1" ERR
+
+      # Ensure a consistent umask.
+      umask 0022
+
+      # Make this configuration the current configuration.
+      # The readlink is there to ensure that when $systemConfig = /system
+      # (which is a symlink to the store), /run/current-system is still
+      # used as a garbage collection root.
+      ln -sfn "$(readlink -f "$systemConfig")" /run/current-system
+
+      # Prevent the current configuration from being garbage-collected.
+      ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+
+      ${cfg.activationScripts.etc.text}
+
+      exit $_status
+    '';
+
+  };
+}
diff --git a/modules/system/etc.nix b/modules/system/etc.nix
new file mode 100644
index 0000000..9999c1e
--- /dev/null
+++ b/modules/system/etc.nix
@@ -0,0 +1,63 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  text = import ./write-text.nix {
+    inherit lib;
+    mkTextDerivation = name: text: pkgs.writeText "etc-${name}" text;
+  };
+
+  etc = filter (f: f.enable) (attrValues config.environment.etc);
+
+in
+
+{
+  options = {
+
+    environment.etc = mkOption {
+      type = types.loaOf (types.submodule text);
+      default = {};
+      description = ''
+        Set of files that have to be linked in <filename>/etc</filename>.
+      '';
+    };
+
+  };
+
+  config = {
+
+    system.build.etc = pkgs.runCommand "etc" {} ''
+      mkdir -p $out/etc
+      cd $out/etc
+      ${concatMapStringsSep "\n" (attr: "ln -s '${attr.source}' '${attr.target}'") etc}
+    '';
+
+    system.activationScripts.etc.text = ''
+      # Set up the statically computed bits of /etc.
+      echo "setting up /etc..."
+
+      ln -sfn "$(readlink -f $systemConfig/etc)" /etc/static
+
+      for link in $(ls /etc/static/); do
+        if [ -e "/etc/$link" ]; then
+          if [ ! -L "/etc/$link" ]; then
+            echo "warning: /etc/$link is a file, skipping..." >&2
+          fi
+        else
+          ln -sfn "/etc/static/$link" "/etc/$link"
+        fi
+      done
+
+      for link in $(find /etc/ -maxdepth 1 -type l); do
+        if [[ "$(readlink $link)" == /etc/static/* ]]; then
+          if [ ! -e "$(readlink -f $link)" ]; then
+            rm $link
+          fi
+        fi
+      done
+    '';
+
+  };
+}
diff --git a/modules/system/write-text.nix b/modules/system/write-text.nix
new file mode 100644
index 0000000..f15fedd
--- /dev/null
+++ b/modules/system/write-text.nix
@@ -0,0 +1,56 @@
+{ lib, mkTextDerivation }:
+
+with lib;
+
+{ config, name, ... }:
+let
+
+  sourceDrv = mkTextDerivation name config.text;
+
+in
+
+{
+  options = {
+
+    enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether this /etc file should be generated.  This
+        option allows specific /etc files to be disabled.
+      '';
+    };
+
+    text = mkOption {
+      default = null;
+      type = types.nullOr types.lines;
+      description = ''
+        Text of the file.
+      '';
+    };
+
+    target = mkOption {
+      type = types.str;
+      default = name;
+      description = ''
+        Name of symlink (relative to
+        <filename>/etc</filename>).  Defaults to the attribute
+        name.
+      '';
+    };
+
+    source = mkOption {
+      type = types.path;
+      description = ''
+        Path of the source file.
+      '';
+    };
+
+  };
+
+  config = {
+
+    source = mkIf (config.text != null) (mkDefault sourceDrv);
+
+  };
+}