// structure, taking into account any necessary alignment.
func CmsgLen(datalen int) int {
	return cmsgAlignOf(SizeofCmsghdr) + datalen
}

// CmsgSpace returns the number of bytes an ancillary element with
// payload of the passed data length occupies.
func CmsgSpace(datalen int) int {
	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
}

func (h *Cmsghdr) data(offset uintptr) unsafe.Pointer {