code: public static void fallocateIfSupported(FileDescriptor fd, long length) throws IOException {
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        LollipopSysdeps.fallocateIfSupported(fd, length);
      }
    }
docs: Pre-allocate disk space for a file if we can do that
  on this version of the OS.
  
  @param fd File descriptor for file
  @param length Number of bytes to allocate.