code: public void writeFallbackInitRequest(long pos) throws IOException {
      Preconditions.checkState(mPartialRequest.getType() == RequestType.UFS_FALLBACK_BLOCK);
      Protocol.CreateUfsBlockOptions ufsBlockOptions = mPartialRequest.getCreateUfsBlockOptions()
          .toBuilder().setBytesInBlockStore(pos).build();
      WriteRequest writeRequest = WriteRequest.newBuilder().setCommand(
          mPartialRequest.toBuilder().setOffset(0).setCreateUfsBlockOptions(ufsBlockOptions))
          .build();
      mPosToQueue = pos;
      mStream.send(writeRequest, mDataTimeoutMs);
    }
docs: Notifies the server UFS fallback endpoint to start writing a new block by resuming the given
  number of bytes from block store.
  
  @param pos number of bytes already written to block store