Sending Data to the Service Provider

The third routine, inter_snd, passes data to the service provider for transmission to the user at the address specified in addr. The data to be transmitted is contained in the buffer pointed to by buf and contains len bytes. On successful completion, this routine returns the number of bytes of data passed to the service provider; on failure, it returns -1.

Example 3-3 inter_snd

inter_snd(int fd, char *buf, int len, long *addr)
{
 	struct strbuf ctlbuf;
 	struct strbuf databuf;
 	struct unitdata_req unitdata_req;

 	unitdata_req.PRIM_type = UNITDATA_REQ;
 	unitdata_req.DEST_addr = addr;

 	ctlbuf.len = sizeof(struct unitdata_req);
 	ctlbuf.buf = (char *)&unitdata_req;
 	databuf.len = len;
 	databuf.buf = buf;

 	if (putmsg(fd, &ctlbuf, &databuf, 0) < 0)
 		return(-1);
	 	return(len);
}

In this example, the data request primitive is packaged with both a control part and a data part. The control part contains a unitdata_req structure that identifies the primitive type and the destination address of the data. The data to be transmitted is placed in the data part of the request message.

Unlike the bind request, the data request primitive requires no acknowledgment from the service provider. In the example, this choice was made to minimize the overhead during data transfer. If the putmsg call succeeds, this routine returns the number of bytes passed to the service provider.