tc-netem: Add support for ECN packet marking

This patch provides support for marking packets with ECN instead of
dropping them with netem. This makes it possible to make use of the
netem ECN marking feature that was added recently to the kernel.
Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com>

tc/q_netem.c

@@ -38,6 +38,7 @@ static void explain(void)
 "                 [ loss random PERCENT [CORRELATION]]\n" \
 "                 [ loss state P13 [P31 [P32 [P23 P14]]]\n" \
 "                 [ loss gemodel PERCENT [R [1-H [1-K]]]\n" \
+"                 [ ecn ]\n" \
 "                 [ reorder PRECENT [CORRELATION] [ gap DISTANCE ]]\n" \
 "                 [ rate RATE [PACKETOVERHEAD] [CELLSIZE] [CELLOVERHEAD]]\n");
 }
@@ -326,6 +327,8 @@ static int netem_parse_opt(struct qdisc_util *qu, int argc, char **argv,
 					*argv);
 				return -1;
 			}
+		} else if (matches(*argv, "ecn") == 0) {
+				present[TCA_NETEM_ECN] = 1;
 		} else if (matches(*argv, "reorder") == 0) {
 			NEXT_ARG();
 			present[TCA_NETEM_REORDER] = 1;
@@ -437,6 +440,14 @@ static int netem_parse_opt(struct qdisc_util *qu, int argc, char **argv,
 		return -1;
 	}
 
+	if (present[TCA_NETEM_ECN]) {
+		if (opt.loss <= 0 && loss_type == NETEM_LOSS_UNSPEC) {
+			fprintf(stderr, "ecn requested without loss model\n");
+			explain();
+			return -1;
+		}
+	}
+
 	if (dist_data && (opt.latency == 0 || opt.jitter == 0)) {
 		fprintf(stderr, "distribution specified but no latency and jitter values\n");
 		explain();
@@ -454,6 +465,11 @@ static int netem_parse_opt(struct qdisc_util *qu, int argc, char **argv,
 	    addattr_l(n, 1024, TCA_NETEM_REORDER, &reorder, sizeof(reorder)) < 0)
 		return -1;
 
+	if (present[TCA_NETEM_ECN] &&
+	    addattr_l(n, 1024, TCA_NETEM_ECN, &present[TCA_NETEM_ECN],
+		      sizeof(present[TCA_NETEM_ECN])) < 0)
+			return -1;
+
 	if (present[TCA_NETEM_CORRUPT] &&
 	    addattr_l(n, 1024, TCA_NETEM_CORRUPT, &corrupt, sizeof(corrupt)) < 0)
 		return -1;
@@ -500,6 +516,7 @@ static int netem_print_opt(struct qdisc_util *qu, FILE *f, struct rtattr *opt)
 	const struct tc_netem_corrupt *corrupt = NULL;
 	const struct tc_netem_gimodel *gimodel = NULL;
 	const struct tc_netem_gemodel *gemodel = NULL;
+	int *ecn = NULL;
 	struct tc_netem_qopt qopt;
 	const struct tc_netem_rate *rate = NULL;
 	int len = RTA_PAYLOAD(opt) - sizeof(qopt);
@@ -548,6 +565,11 @@ static int netem_print_opt(struct qdisc_util *qu, FILE *f, struct rtattr *opt)
 				return -1;
 			rate = RTA_DATA(tb[TCA_NETEM_RATE]);
 		}
+		if (tb[TCA_NETEM_ECN]) {
+			if (RTA_PAYLOAD(tb[TCA_NETEM_ECN]) < sizeof(*ecn))
+				return -1;
+			ecn = RTA_DATA(tb[TCA_NETEM_ECN]);
+		}
 	}
 
 	fprintf(f, "limit %d", qopt.limit);
@@ -617,9 +639,13 @@ static int netem_print_opt(struct qdisc_util *qu, FILE *f, struct rtattr *opt)
 			fprintf(f, " celloverhead %d", rate->cell_overhead);
 	}
 
+	if (ecn)
+		fprintf(f, " ecn ");
+
 	if (qopt.gap)
 		fprintf(f, " gap %lu", (unsigned long)qopt.gap);
 
+
 	return 0;
 }