public void link(Name name, File file) {
    DirectoryEntry entry = new DirectoryEntry(this, checkNotReserved(name, "link"), file);
    put(entry);
    file.linked(entry);
  }
Links the given name to the given file in this directory.

@throws IllegalArgumentException if {@code name} is a reserved name such as "." or if an entry
    already exists for the name
jimfs/src/main/java/com/google/common/jimfs/Directory.java