tc: add support for plug qdisc

sch_plug can be used to perform functional qdisc unit tests
controlling explicitly the queuing behaviour from user-space.

Plug support lacks since its introduction in 2012. This change
introduces basic support, to control the tc status.

v1 -> v2:
 - use the SPDX identifier

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>

tc/Makefile

@@ -75,6 +75,7 @@ TCMODULES += f_matchall.o
 TCMODULES += q_cbs.o
 TCMODULES += q_etf.o
 TCMODULES += q_taprio.o
+TCMODULES += q_plug.o
 
 TCSO :=
 ifeq ($(TC_CONFIG_ATM),y)

tc/q_plug.c

@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * q_log.c		plug scheduler
+ *
+ * Copyright (C) 2019	Paolo Abeni <pabeni@redhat.com>
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <string.h>
+
+#include "utils.h"
+#include "tc_util.h"
+
+static void explain(void)
+{
+	fprintf(stderr, "Usage: ... plug [block | release | release_indefinite | limit NUMBER]\n");
+}
+
+static int plug_parse_opt(struct qdisc_util *qu, int argc, char **argv,
+			  struct nlmsghdr *n, const char *dev)
+{
+	struct tc_plug_qopt opt = {};
+	int ok = 0;
+
+	while (argc > 0) {
+		if (strcmp(*argv, "block") == 0) {
+			opt.action = TCQ_PLUG_BUFFER;
+			ok++;
+		} else if (strcmp(*argv, "release") == 0) {
+			opt.action = TCQ_PLUG_RELEASE_ONE;
+			ok++;
+		} else if (strcmp(*argv, "release_indefinite") == 0) {
+			opt.action = TCQ_PLUG_RELEASE_INDEFINITE;
+			ok++;
+		} else if (strcmp(*argv, "limit") == 0) {
+			opt.action = TCQ_PLUG_LIMIT;
+			NEXT_ARG();
+			if (get_size(&opt.limit, *argv)) {
+				fprintf(stderr, "Illegal value for \"limit\": \"%s\"\n", *argv);
+				return -1;
+			}
+			ok++;
+		} else if (strcmp(*argv, "help") == 0) {
+			explain();
+			return -1;
+		} else {
+			fprintf(stderr, "%s: unknown parameter \"%s\"\n", qu->id, *argv);
+			explain();
+			return -1;
+		}
+		argc--; argv++;
+	}
+
+	if (ok)
+		addattr_l(n, 1024, TCA_OPTIONS, &opt, sizeof(opt));
+	return 0;
+}
+
+static int plug_print_opt(struct qdisc_util *qu, FILE *f, struct rtattr *opt)
+{
+	/* dummy implementation as sch_plug does not implement a dump op */
+	return 0;
+}
+
+
+struct qdisc_util plug_qdisc_util = {
+	.id = "plug",
+	.parse_qopt = plug_parse_opt,
+	.print_qopt = plug_print_opt,
+};