Update btrfs-backup script. Add lock file generation

nixos/common/software/cli/scripts/btrfs-backup.sh

@@ -32,6 +32,36 @@ if ! command -v snapper >/dev/null 2>&1 || \
     exit 1
 fi
 
+# Lock file handling
+LOCK_FILE="/var/run/btrfs-backup-${1}.lock"
+
+# Lock file creation with cleanup
+cleanup_lock() {
+    rm -f "$LOCK_FILE"
+}
+
+create_lock() {
+    if [ -e "$LOCK_FILE" ]; then
+        # Check if the process is still running
+        if pid=$(cat "$LOCK_FILE" 2>/dev/null) && kill -0 "$pid" 2>/dev/null; then
+            echo "ERROR: Another backup process (PID: $pid) is already running"
+            exit 1
+        else
+            # Lock file exists but process is not running, remove stale lock
+            rm -f "$LOCK_FILE"
+        fi
+    fi
+
+    # Create new lock file with current PID
+    echo $$ > "$LOCK_FILE"
+
+    # Ensure lock file is removed on script exit
+    trap cleanup_lock EXIT
+}
+
+# Create lock file
+create_lock
+
 # Help function
 show_help() {
     cat << EOF
@@ -117,12 +147,16 @@ cleanup() {
             sudo snapper -c "$SNAPPER_CONFIG" delete "$NEW_SNAPSHOT" || true
         fi
     fi
+
+    # Remove lock file
+    cleanup_lock
+
     exit $exit_code
 }
 
 # Set up traps
 trap 'error_handler ${LINENO} $?' ERR
-trap cleanup EXIT
+trap cleanup EXIT INT TERM
 
 # Get the actual snapshot location from snapper config
 SOURCE_PATH=$(sudo snapper -c "$SNAPPER_CONFIG" get-config | grep '^SUBVOLUME' | cut -d'=' -f2 | tr -d '"'| awk {'print $3'})