This \link{GSocketControlMessage} contains a list of file descriptors.
It may be sent using gSocketSendMessage and received using
gSocketReceiveMessage over UNIX sockets (ie: sockets in the
G_SOCKET_ADDRESS_UNIX family). For an easier way to send and receive file descriptors over
stream-oriented UNIX sockets, see gUnixConnectionSendFd() and
gUnixConnectionReceiveFd().