Support setting the IPv6 flow label on Linux systems (only).

This functionality uses some setsockopt(2) calls that unfortunately
don't seem to have an analog on other platforms.

Slightly tweaked version of a patch that was...

Submitted by:	ssahani@redhat.com
Issue:		40 (Option for setting Flow Label field in IPv6
		header)

src/iperf3.1

@@ -109,9 +109,9 @@ only use IPv6
 .TP
 .BR -S ", " --tos " \fIn\fR"
 set the IP 'type of service'
-.\" .TP
-.\" .BR -L ", " --flowlabel " \fIn\fR"
-.\" set the IPv6 'flow label'
+.TP
+.BR -L ", " --flowlabel " \fIn\fR"
+set the IPv6 flow label (currently only supported on Linux)
 .TP
 .BR -Z ", " --zerocopy " "
 Use a "zero copy" method of sending data, such as sendfile(2),

src/iperf_api.c

@@ -655,17 +655,17 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
 		client_flag = 1;
                 break;
             case 'L':
-#ifdef notdef
+#if defined(linux)
                 test->settings->flowlabel = strtol(optarg, NULL, 0);
 		if (test->settings->flowlabel < 1 || test->settings->flowlabel > 0xfffff) {
                     i_errno = IESETFLOW;
                     return -1;
 		}
 		client_flag = 1;
-#else /* notdef */
-		i_errno = IEUNIMP;
-		return -1;
-#endif /* notdef */
+#else /* linux */
+                i_errno = IEUNIMP;
+                return -1;
+#endif /* linux */
                 break;
             case 'Z':
                 if (!has_sendfile()) {

src/iperf_tcp.c

@@ -25,6 +25,9 @@
 #include "iperf_tcp.h"
 #include "net.h"
 
+#if defined(linux)
+#include "flowlabel.h"
+#endif
 
 /* iperf_tcp_recv
  *
@@ -291,6 +294,7 @@ iperf_tcp_connect(struct iperf_test *test)
             return -1;
         }
     }
+#if defined(linux)
     if (test->settings->flowlabel) {
         if (server_res->ai_addr->sa_family != AF_INET6) {
 	    close(s);
@@ -299,9 +303,35 @@ iperf_tcp_connect(struct iperf_test *test)
             return -1;
 	} else {
 	    struct sockaddr_in6* sa6P = (struct sockaddr_in6*) server_res->ai_addr;
-	    sa6P->sin6_flowinfo = htonl(test->settings->flowlabel);
+            char freq_buf[sizeof(struct in6_flowlabel_req)];
+            struct in6_flowlabel_req *freq = (struct in6_flowlabel_req *)freq_buf;
+            int freq_len = sizeof(*freq);
+
+            memset(freq, 0, sizeof(*freq));
+            freq->flr_label = htonl(test->settings->flowlabel & IPV6_FLOWINFO_FLOWLABEL);
+            freq->flr_action = IPV6_FL_A_GET;
+            freq->flr_flags = IPV6_FL_F_CREATE;
+            freq->flr_share = IPV6_FL_F_CREATE | IPV6_FL_S_EXCL;
+            memcpy(&freq->flr_dst, &sa6P->sin6_addr, 16);
+
+            if (setsockopt(s, IPPROTO_IPV6, IPV6_FLOWLABEL_MGR, freq, freq_len) < 0) {
+                close(s);
+                freeaddrinfo(server_res);
+                i_errno = IESETFLOW;
+                return -1;
+            }
+            sa6P->sin6_flowinfo = freq->flr_label;
+
+            opt = 1;
+            if (setsockopt(s, IPPROTO_IPV6, IPV6_FLOWINFO_SEND, &opt, sizeof(opt)) < 0) {
+                close(s);
+                freeaddrinfo(server_res);
+                i_errno = IESETFLOW;
+                return -1;
+            } 
 	}
     }
+#endif
 
     if (connect(s, (struct sockaddr *) server_res->ai_addr, server_res->ai_addrlen) < 0 && errno != EINPROGRESS) {
 	close(s);

src/locale.c

@@ -99,7 +99,9 @@ const char usage_longstr[] = "Usage: iperf [-s|-c host] [options]\n"
                            "  -4, --version4            only use IPv4\n"
                            "  -6, --version6            only use IPv6\n"
                            "  -S, --tos N               set the IP 'type of service'\n"
-                           /* "  -L, --flowlabel N         set the IPv6 'flow label'\n" */
+#if defined(linux)
+                           "  -L, --flowlabel N         set the IPv6 flow label (only supported on Linux)\n"
+#endif
                            "  -Z, --zerocopy            use a 'zero copy' method of sending data\n"
                            "  -O, --omit N              omit the first n seconds\n"
                            "  -T, --title str           prefix every output line with this string\n"