code: func importPreimages(ctx *cli.Context) error {
  	if len(ctx.Args()) < 1 {
  		utils.Fatalf("This command requires an argument.")
  	}
  	stack := makeFullNode(ctx)
  	defer stack.Close()
  
  	db := utils.MakeChainDatabase(ctx, stack)
  	start := time.Now()
  
  	if err := utils.ImportPreimages(db, ctx.Args().First()); err != nil {
  		utils.Fatalf("Import error: %v\n", err)
  	}
  	fmt.Printf("Import done in %v\n", time.Since(start))
  	return nil
  }
docs: // importPreimages imports preimage data from the specified file.