Move hosts/ahmed/disable-screen.nix into a proper module

2 files changed, 66 insertions, 0 deletions

diff --git a/modules/nixos/default.nix b/modules/nixos/default.nix
index 9ad08e5..daea05f 100644
--- a/modules/nixos/default.nix
+++ b/modules/nixos/default.nix
@@ -7,4 +7,6 @@
   ## Other miscellaneous configuration bits. These may be useful to other you.
 
   cloudflare-proxy = import ./cloudflare-proxy;
+
+  disable-screen = import ./disable-screen;
 }
diff --git a/modules/nixos/disable-screen/default.nix b/modules/nixos/disable-screen/default.nix
new file mode 100644
index 0000000..b70d80d
--- /dev/null
+++ b/modules/nixos/disable-screen/default.nix
@@ -0,0 +1,64 @@
+# This file defines some configuration options which disable the screen. This
+# is only relevant because this host is an old laptop running as a server.
+
+{ lib, config, ... }:
+
+let
+  inherit (lib) mkEnableOption mkOption types;
+
+  cfg = config.disable-screen;
+in
+{
+  options.disable-screen = {
+    enable = mkEnableOption "disable screen";
+
+    device-path = mkOption {
+      description = "Path to the device in the `/sys` file system.";
+      type = types.str;
+      example = "/sys/class/backlight/intel_backlight";
+    };
+
+    device-unit = mkOption {
+      description = "The systemd device unit that corresponds to the device speciefied in `device-path`.";
+      type = types.str;
+      example = "sys-devices-pci...-intel_backligt.device";
+    };
+  };
+
+  config = {
+    # Disable sleep on lid close.
+    services.logind =
+      let
+        lidSwitchAction = "ignore";
+      in
+      {
+        lidSwitchExternalPower = lidSwitchAction;
+        lidSwitchDocked = lidSwitchAction;
+        lidSwitch = lidSwitchAction;
+      };
+
+    # Don't store screen brightness between boots. We always want to turn off the
+    # screen.
+    #
+    # See: https://wiki.archlinux.org/title/backlight#Save_and_restore_functionality
+    # See: https://github.com/NixOS/nixpkgs/blob/990398921f677615c0732d704857484b84c6c888/nixos/modules/system/boot/systemd.nix#L97-L101
+    systemd.suppressedSystemUnits = [ "[email protected]" ];
+
+    # FIXME: Figure out how to enable screen when on-device debugging is necessary.
+    # Create a new service which turns off the display on boot.
+    #
+    # See: https://nixos.wiki/wiki/Backlight#.2Fsys.2Fclass.2Fbacklight.2F...
+    # See: https://superuser.com/questions/851846/how-to-write-a-systemd-service-that-depends-on-a-device-being-present
+    systemd.services.disable-screen =
+      {
+        requires = [ cfg.device-unit ];
+        after = [ cfg.device-unit ];
+        wantedBy = [ cfg.device-unit ];
+
+        serviceConfig.Type = "oneshot";
+        script = ''
+          tee ${cfg.device-path}/brightness <<<0
+        '';
+      };
+  };
+}