net-timestamp: no-payload option in txtimestamp test

Demonstrate how SOF_TIMESTAMPING_OPT_TSONLY can be used and
test the implementation.

Signed-off-by: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/timestamping/txtimestamp.c

···
 static int cfg_payload_len = 10;
 static bool cfg_show_payload;
 static bool cfg_do_pktinfo;
+static bool cfg_loop_nodata;
 static uint16_t dest_port = 9000;
 
 static struct sockaddr_in daddr;
···
 {
 	int i;
 
+	if (!len)
+		return;
+
 	if (len > 70)
 		len = 70;
 
···
 	struct sock_extended_err *serr = NULL;
 	struct scm_timestamping *tss = NULL;
 	struct cmsghdr *cm;
+	int batch = 0;
 
 	for (cm = CMSG_FIRSTHDR(msg);
 	     cm && cm->cmsg_len;
···
 		} else
 			fprintf(stderr, "unknown cmsg %d,%d\n",
 					cm->cmsg_level, cm->cmsg_type);
+
+		if (serr && tss) {
+			print_timestamp(tss, serr->ee_info, serr->ee_data,
+					payload_len);
+			serr = NULL;
+			tss = NULL;
+			batch++;
+		}
 	}
 
-	if (serr && tss)
-		print_timestamp(tss, serr->ee_info, serr->ee_data, payload_len);
+	if (batch > 1)
+		fprintf(stderr, "batched %d timestamps\n", batch);
 }
 
 static int recv_errmsg(int fd)
···
 	if (ret == -1 && errno != EAGAIN)
 		error(1, errno, "recvmsg");
 
-	if (ret > 0) {
+	if (ret >= 0) {
 		__recv_errmsg_cmsg(&msg, ret);
 		if (cfg_show_payload)
 			print_payload(data, cfg_payload_len);
···
 	opt |= SOF_TIMESTAMPING_SOFTWARE |
 	       SOF_TIMESTAMPING_OPT_CMSG |
 	       SOF_TIMESTAMPING_OPT_ID;
+	if (cfg_loop_nodata)
+		opt |= SOF_TIMESTAMPING_OPT_TSONLY;
+
 	if (setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING,
 		       (char *) &opt, sizeof(opt)))
 		error(1, 0, "setsockopt timestamping");
···
 			"  -h:   show this message\n"
 			"  -I:   request PKTINFO\n"
 			"  -l N: send N bytes at a time\n"
+			"  -n:   set no-payload option\n"
 			"  -r:   use raw\n"
 			"  -R:   use raw (IP_HDRINCL)\n"
 			"  -p N: connect to port N\n"
···
 	int proto_count = 0;
 	char c;
 
-	while ((c = getopt(argc, argv, "46hIl:p:rRux")) != -1) {
+	while ((c = getopt(argc, argv, "46hIl:np:rRux")) != -1) {
 		switch (c) {
 		case '4':
 			do_ipv6 = 0;
···
 			break;
 		case 'I':
 			cfg_do_pktinfo = true;
+			break;
+		case 'n':
+			cfg_loop_nodata = true;
 			break;
 		case 'r':
 			proto_count++;