code: func (r *Reader) FindKey(key []byte, filtered bool, ro *opt.ReadOptions) (rkey []byte, err error) {
  	rkey, _, err = r.find(key, filtered, ro, true)
  	return
  }
docs: // FindKey finds key that is greater than or equal to the given key.
  // It returns ErrNotFound if the table doesn't contain such key.
  // If filtered is true then the nearest 'block' will be checked against
  // 'filter data' (if present) and will immediately return ErrNotFound if
  // 'filter data' indicates that such key doesn't exist.
  //
  // The caller may modify the contents of the returned slice as it is its
  // own copy.
  // It is safe to modify the contents of the argument after Find returns.