code: private static JimfsFileStore createFileStore(
        Configuration config, PathService pathService, FileSystemState state) {
      AttributeService attributeService = new AttributeService(config);
  
      // TODO(cgdecker): Make disk values configurable
      HeapDisk disk = new HeapDisk(config);
      FileFactory fileFactory = new FileFactory(disk);
  
      Map<Name, Directory> roots = new HashMap<>();
  
      // create roots
      for (String root : config.roots) {
        JimfsPath path = pathService.parsePath(root);
        if (!path.isAbsolute() && path.getNameCount() == 0) {
          throw new IllegalArgumentException("Invalid root path: " + root);
        }
  
        Name rootName = path.root();
  
        Directory rootDir = fileFactory.createRootDirectory(rootName);
        attributeService.setInitialAttributes(rootDir);
        roots.put(rootName, rootDir);
      }
  
      return new JimfsFileStore(
          new FileTree(roots), fileFactory, disk, attributeService, config.supportedFeatures, state);
    }
docs: Creates the file store for the file system.