TCP_INFO documented

SRC/DETAILS

@@ -29,11 +29,18 @@ physical line raw throughput measures (unlike bing). On the other end,
 the action it performs are close from a HTTP request and it is
 meaningful to use it (carefully) to measure Web performances.
 
+More on Linux:
+
+On operating systems, like Linux, who have the TCP_INFO option (see
+http://linuxgazette.net/136/pfeiffer.html for a detailed
+presentation), echoping can also display interesting TCP information.
+
 UDP and inetd:
 
 With UDP servers you can have surprises: the first test is quite often
-much slower since inetd has to launch the process. After that, the
-process stays a while so the next texts run faster.
+much slower since inetd or xinetd typically has to launch the
+process. After that, the process stays a while so the next texts run
+faster.
 
 A nice example:
 

SRC/echoping.c

@@ -699,7 +699,7 @@ main(argc, argv)
 	if (smtp) {
 		sendline = "QUIT\r\n";	/* Surprises some SMTP servers which log a
 					 * frightening NOQUEUE. Anyone knows better? 
-					 * See bug #1512776 */
+					 * * See bug #1512776 */
 	} else
 #endif
 #ifdef ICP
@@ -1346,13 +1346,21 @@ main(argc, argv)
 		}		/* That's all, folks */
 		alarm(0);
 #ifdef HAVE_TCP_INFO
-		/* Thanks to Perry Lorier <perry@coders.net> for the tip */
+		/* Thanks to Perry Lorier <perry@coders.net> for the tip. See a
+		 * longer paper in http://linuxgazette.net/136/pfeiffer.html */
 		if (tcp && verbose) {
 			if (getsockopt
 			    (sockfd, SOL_TCP, TCP_INFO, &tcpinfo, &socket_length)
 			    != -1) {
-				printf("Estimated TCP RTT: %.04f seconds\n",
-				       tcpinfo.tcpi_rtt / 1000000.0);
+				/* TODO: find out the meaning of the various fields
+				 * inthe struct tcp_info (it seems documented only
+				 * in the Linux kernel sources) and display stuff
+				 * like reordering (see RFC 4737), window, lost
+				 * packets, etc. */
+				printf
+				    ("Estimated TCP RTT: %.04f seconds (std. deviation %0.03f)\n",
+				     tcpinfo.tcpi_rtt / 1000000.0,
+				     tcpinfo.tcpi_rttvar / 1000000.0);
 			}
 		}
 #endif

Web/details.wml

@@ -24,6 +24,12 @@ line raw throughput measures (unlike bing). On the other end, the action it
 performs are close from a HTTP request and it is meaningful to use it 
 (carefully) to measure Web performances. 
 
+<H3>More on Linux</H3>
+
+<P>On operating systems, like Linux, who have the TCP_INFO option (see
+<A HREF="http://linuxgazette.net/136/pfeiffer.html">a detailed
+presentation</A>), echoping can also display interesting TCP information.
+
 <H2>UDP and inetd</H2>
 
 <P>With UDP servers you can have surprises: the first test is quite often