code: private void transferToUfsBlock(BlockWriteRequestContext context, long pos) throws Exception {
      OutputStream ufsOutputStream = context.getOutputStream();
  
      long sessionId = context.getRequest().getSessionId();
      long blockId = context.getRequest().getId();
      TempBlockMeta block = mWorker.getBlockStore().getTempBlockMeta(sessionId, blockId);
      if (block == null) {
        throw new NotFoundException("block " + blockId + " not found");
      }
      Preconditions.checkState(Files.copy(Paths.get(block.getPath()), ufsOutputStream) == pos);
    }
docs: Transfers data from block store to UFS.
  
  @param context context of this request
  @param pos number of bytes in block store to write in the UFS block