The following gets a
MathLink connection and uses it to send a message to the kernel:
MLINK link = libData->getMathLink(libData);
MLPutFunction( link, "EvaluatePacket", 1);
MLPutFunction( link, "Message", 2);
MLPutFunction( link, "MessageName", 2);
MLPutSymbol( link, "MyFunction");
MLPutString( link, "info");
MLPutString( link, "Message called from within DLL function.");
libData->processMathLink( link);
pkt = MLNextPacket( link);
if ( pkt == RETURNPKT) {
MLNewPacket(link);
}