mach_msg trouble

[Constantine Kousoulos]

I'm trying to set up a simple server that just receives messages
(not threaded). So, i have written

 /* for port allocation */
  ipc_space_t ist;
  kern_return_t port_err;
  mach_port_t name;
  task_t self;

  /* for message reception */
  mach_msg_return_t msg_err;
  mach_msg_header_t msg_body;

  port_err=mach_port_allocate(mach_task_self(),
MACH_PORT_RIGHT_RECEIVE, &name);
  if (port_err!=KERN_SUCCESS)
    error(1, port_err, "cannot allocate port, %d", port_err);

  msg_err=mach_msg(&msg_body, MACH_RCV_MSG, 0, sizeof(msg_body),
                        XXX,
                        MACH_MSG_TIMEOUT_NONE,
                        MACH_PORT_NULL);
  if (msg_err!=MACH_MSG_SUCCESS)
    error(1, msg_err, "error receiving message, %d", msg_err);

I don't know what to put instead of XXX to make this task
reveive messages at the allocated port.

Secondly, how can a client discover this server's port in order to 
send something?

Any help is appreciated!

Thanks,
Constantine