sendmsg, recvmsg and ancillary data operations

 Socket::MsgHdr provides advanced socket messaging operations via sendmsg and
 recvmsg. Like their C counterparts, these functions accept few parameters,
 instead stuffing a lot of information into a complex structure.
 .
 This structure describes the message sent or received (buf), the peer on the
 other end of the socket (name), and ancillary or so-called control
 information (cmsghdr). This ancillary data may be used for file descriptor
 passing, IPv6 operations, and a host of implemenation-specific extensions.