nixos/usbStorage: add new option

nixos/modules/hardware/usb-storage.nix

@@ -0,0 +1,20 @@
+{ config, lib, pkgs, ... }:
+with lib;
+
+{
+  options.hardware.usbStorage.manageStartStop = mkOption {
+    type = types.bool;
+    default = true;
+    description = lib.mdDoc ''
+      Enable this option to gracefully spin-down external storage during shutdown.
+      If you suspect improper head parking after poweroff, install `smartmontools` and check
+      for the `Power-Off_Retract_Count` field for an increment.
+    '';
+  };
+
+  config = mkIf config.hardware.usbStorage.manageStartStop {
+    services.udev.extraRules = ''
+      ACTION=="add|change", SUBSYSTEM=="scsi_disk", DRIVERS=="usb-storage", ATTR{manage_start_stop}="1"
+    '';
+  };
+}

nixos/modules/module-list.nix

@@ -81,6 +81,7 @@
   ./hardware/tuxedo-keyboard.nix
   ./hardware/ubertooth.nix
   ./hardware/usb-wwan.nix
+  ./hardware/usb-storage.nix
   ./hardware/onlykey/default.nix
   ./hardware/opentabletdriver.nix
   ./hardware/sata.nix