code: func (w *AtomicWriter) createUserVisibleFiles(payload map[string]FileProjection) error {
  	for userVisiblePath := range payload {
  		slashpos := strings.Index(userVisiblePath, string(os.PathSeparator))
  		if slashpos == -1 {
  			slashpos = len(userVisiblePath)
  		}
  		linkname := userVisiblePath[:slashpos]
  		_, err := os.Readlink(filepath.Join(w.targetDir, linkname))
  		if err != nil && os.IsNotExist(err) {
  			// The link into the data directory for this path doesn't exist; create it
  			visibleFile := filepath.Join(w.targetDir, linkname)
  			dataDirFile := filepath.Join(dataDirName, linkname)
  
  			err = os.Symlink(dataDirFile, visibleFile)
  			if err != nil {
  				return err
  			}
  		}
  	}
  	return nil
  }
docs: // createUserVisibleFiles creates the relative symlinks for all the
  // files configured in the payload. If the directory in a file path does not
  // exist, it is created.
  //
  // Viz:
  // For files: "bar", "foo/bar", "baz/bar", "foo/baz/blah"
  // the following symlinks are created:
  // bar -> ..data/bar
  // foo -> ..data/foo
  // baz -> ..data/baz