code: public void initializeRoot(String owner, String group, Mode mode, JournalContext context)
        throws UnavailableException {
      if (mState.getRoot() == null) {
        MutableInodeDirectory root = MutableInodeDirectory.create(
            mDirectoryIdGenerator.getNewDirectoryId(context), NO_PARENT, ROOT_INODE_NAME,
            CreateDirectoryContext
                .mergeFrom(CreateDirectoryPOptions.newBuilder().setMode(mode.toProto()))
                .setOwner(owner).setGroup(group));
        root.setPersistenceState(PersistenceState.PERSISTED);
        mState.applyAndJournal(context, root);
      }
    }
docs: Initializes the root of the inode tree.
  
  @param owner the root owner
  @param group the root group
  @param mode the root mode
  @param context the journal context to journal the initialization to