tools: ynl: add a sample for TC

Add a very simple TC dump sample with decoding of fq_codel attrs:

  # ./tools/net/ynl/samples/tc
        dummy0: fq_codel  limit: 10240p target: 5ms new_flow_cnt: 0

proving that selector passing (for stats) works.

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250520161916.413298-13-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 81 insertions, 0 deletions

diff --git a/tools/net/ynl/samples/.gitignore b/tools/net/ynl/samples/.gitignore
index b3ec3fb0929f..7f5fca7682d7 100644
--- a/tools/net/ynl/samples/.gitignore
+++ b/tools/net/ynl/samples/.gitignore
@@ -6,3 +6,4 @@ page-pool
 rt-addr
 rt-link
 rt-route
+tc
diff --git a/tools/net/ynl/samples/tc.c b/tools/net/ynl/samples/tc.c
new file mode 100644
index 000000000000..0bfff0fdd792
--- /dev/null
+++ b/tools/net/ynl/samples/tc.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <string.h>
+
+#include <ynl.h>
+
+#include <net/if.h>
+
+#include "tc-user.h"
+
+static void tc_qdisc_print(struct tc_getqdisc_rsp *q)
+{
+	char ifname[IF_NAMESIZE];
+	const char *name;
+
+	name = if_indextoname(q->_hdr.tcm_ifindex, ifname);
+	if (name)
+		printf("%16s: ", name);
+
+	if (q->_len.kind) {
+		printf("%s  ", q->kind);
+
+		if (q->options._present.fq_codel) {
+			struct tc_fq_codel_attrs *fq_codel;
+			struct tc_fq_codel_xstats *stats;
+
+			fq_codel = &q->options.fq_codel;
+			stats = q->stats2.app.fq_codel;
+
+			if (fq_codel->_present.limit)
+				printf("limit: %dp ", fq_codel->limit);
+			if (fq_codel->_present.target)
+				printf("target: %dms ",
+				       (fq_codel->target + 500) / 1000);
+			if (q->stats2.app._len.fq_codel)
+				printf("new_flow_cnt: %d ",
+				       stats->qdisc_stats.new_flow_count);
+		}
+	}
+
+	printf("\n");
+}
+
+int main(int argc, char **argv)
+{
+	struct tc_getqdisc_req_dump *req;
+	struct tc_getqdisc_list *rsp;
+	struct ynl_error yerr;
+	struct ynl_sock *ys;
+
+	ys = ynl_sock_create(&ynl_tc_family, &yerr);
+	if (!ys) {
+		fprintf(stderr, "YNL: %s\n", yerr.msg);
+		return 1;
+	}
+
+	req = tc_getqdisc_req_dump_alloc();
+	if (!req)
+		goto err_destroy;
+
+	rsp = tc_getqdisc_dump(ys, req);
+	tc_getqdisc_req_dump_free(req);
+	if (!rsp)
+		goto err_close;
+
+	if (ynl_dump_empty(rsp))
+		fprintf(stderr, "Error: no addresses reported\n");
+	ynl_dump_foreach(rsp, qdisc)
+		tc_qdisc_print(qdisc);
+	tc_getqdisc_list_free(rsp);
+
+	ynl_sock_destroy(ys);
+	return 0;
+
+err_close:
+	fprintf(stderr, "YNL: %s\n", ys->err.msg);
+err_destroy:
+	ynl_sock_destroy(ys);
+	return 2;
+}