code: private void updateUnderFileSystemInputStream(long offset) throws IOException {
      if ((mUnderFileSystemInputStream != null) && offset != mInStreamPos) {
        mUfsInstreamManager.release(mUnderFileSystemInputStream);
        mUnderFileSystemInputStream = null;
        mInStreamPos = -1;
      }
  
      if (mUnderFileSystemInputStream == null && offset < mBlockMeta.getBlockSize()) {
        UnderFileSystem ufs = mUfsResource.get();
        mUnderFileSystemInputStream = mUfsInstreamManager.acquire(ufs,
            mBlockMeta.getUnderFileSystemPath(), IdUtils.fileIdFromBlockId(mBlockMeta.getBlockId()),
            OpenOptions.defaults().setOffset(mBlockMeta.getOffset() + offset));
        mInStreamPos = offset;
      }
    }
docs: Updates the UFS input stream given an offset to read.
  
  @param offset the read offset within the block