Update configuration.nix

configuration.nix

@@ -135,13 +135,13 @@
   ############################################################
 
   systemd.services.shutdown-on-root-usb-loss = {
-    description = "Shutdown if USB device backing / disappears";
+    description = "Shutdown if device backing / disappears";
     wantedBy = [ "multi-user.target" ];
     after = [ "local-fs.target" ];
 
     serviceConfig = {
       Type = "simple";
-      ExecStart = pkgs.writeShellScript "watch-root-usb" ''
+      ExecStart = pkgs.writeShellScript "watch-root-device" ''
         set -e
 
         FINDMNT=${pkgs.util-linux}/bin/findmnt
@@ -150,23 +150,21 @@
         SLEEP=${pkgs.coreutils}/bin/sleep
         SYSTEMCTL=${pkgs.systemd}/bin/systemctl
 
+        # Resolve root source
         ROOT_SRC="$($FINDMNT -n -o SOURCE / || true)"
         [ -z "$ROOT_SRC" ] && exit 0
 
-        if [[ "$ROOT_SRC" == /dev/dm-* ]]; then
-          PARENT="$($LSBLK -no PKNAME "$ROOT_SRC")"
-          ROOT_DEV="/dev/$PARENT"
-        else
-          ROOT_DEV="$ROOT_SRC"
-        fi
+        # Walk up to the top-level block device
+        DEV="$ROOT_SRC"
+        while PARENT="$($LSBLK -no PKNAME "$DEV" 2>/dev/null)"; [ -n "$PARENT" ]; do
+          DEV="/dev/$PARENT"
+        done
 
-        TRAN="$($LSBLK -no TRAN "$ROOT_DEV" || true)"
-        [ "$TRAN" != "usb" ] && exec $SLEEP infinity
-
-        DEV_NAME="$($BASENAME "$ROOT_DEV")"
+        DEV_NAME="$($BASENAME "$DEV")"
 
+        # Watch until the block device disappears
         while [ -e "/sys/class/block/$DEV_NAME" ]; do
-          $SLEEP 1
+          $SLEEP 0.5
         done
 
         $SYSTEMCTL poweroff