code: func (cp *CPUManagerCheckpoint) VerifyChecksum() error {
  	if cp.Checksum == 0 {
  		// accept empty checksum for compatibility with old file backend
  		return nil
  	}
  	ck := cp.Checksum
  	cp.Checksum = 0
  	err := ck.Verify(cp)
  	cp.Checksum = ck
  	return err
  }
docs: // VerifyChecksum verifies that current checksum of checkpoint is valid