code: func AreVolumeCapabilitiesCompatible(
  	a, b []*csi.VolumeCapability) (bool, error) {
  
  	if len(a) > len(b) {
  		return false, status.Error(
  			codes.AlreadyExists,
  			"requested capabilities exceed existing")
  	}
  
  	var i int
  
  	for _, va := range a {
  		for _, vb := range b {
  			if EqualVolumeCapability(va, vb) {
  				i++
  			}
  		}
  	}
  
  	return i >= len(a), nil
  }
docs: // AreVolumeCapabilitiesCompatible returns a flag indicating whether
  // the volume capability array "a" is compatible with "b". A true value
  // indicates that "a" and "b" are equivalent or "b" is a superset of "a".