docs: public static long padLogFile(FileOutputStream f,long currentSize,
              long preAllocSize) throws IOException{
          long position = f.getChannel().position();
          if (position + 4096 >= currentSize) {
              currentSize = currentSize + preAllocSize;
              fill.position(0);
              f.getChannel().write(fill, currentSize-fill.remaining());
          }
          return currentSize;
      }