code: func (txn *tikvTxn) IterReverse(k kv.Key) (kv.Iterator, error) {
  	tikvTxnCmdCountWithSeekReverse.Inc()
  	start := time.Now()
  	defer func() {
  		tikvTxnCmdHistogramWithSeekReverse.Observe(time.Since(start).Seconds())
  	}()
  
  	return txn.us.IterReverse(k)
  }
docs: // IterReverse creates a reversed Iterator positioned on the first entry which key is less than k.