tools: ynl: add sample for ethtool

Configuring / reading ring sizes and counts is a fairly common
operation for ethtool netlink. Present a sample doing that with
YNL:

$ ./ethtool
Channels:
    enp1s0: combined 1
   eni1np1: combined 1
   eni2np1: combined 1
Rings:
    enp1s0: rx 256 tx 256
   eni1np1: rx 0 tx 0
   eni2np1: rx 0 tx 0
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/net/ynl/samples/.gitignore

+ethtool
 devlink
 netdev

tools/net/ynl/samples/ethtool.c

+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <string.h>
+
+#include <ynl.h>
+
+#include <net/if.h>
+
+#include "ethtool-user.h"
+
+int main(int argc, char **argv)
+{
+	struct ethtool_channels_get_req_dump creq = {};
+	struct ethtool_rings_get_req_dump rreq = {};
+	struct ethtool_channels_get_list *channels;
+	struct ethtool_rings_get_list *rings;
+	struct ynl_sock *ys;
+
+	ys = ynl_sock_create(&ynl_ethtool_family, NULL);
+	if (!ys)
+		return 1;
+
+	creq._present.header = 1; /* ethtool needs an empty nest, sigh */
+	channels = ethtool_channels_get_dump(ys, &creq);
+	if (!channels)
+		goto err_close;
+
+	printf("Channels:\n");
+	ynl_dump_foreach(channels, dev) {
+		printf("  %8s: ", dev->header.dev_name);
+		if (dev->_present.rx_count)
+			printf("rx %d ", dev->rx_count);
+		if (dev->_present.tx_count)
+			printf("tx %d ", dev->tx_count);
+		if (dev->_present.combined_count)
+			printf("combined %d ", dev->combined_count);
+		printf("\n");
+	}
+	ethtool_channels_get_list_free(channels);
+
+	rreq._present.header = 1; /* ethtool needs an empty nest.. */
+	rings = ethtool_rings_get_dump(ys, &rreq);
+	if (!rings)
+		goto err_close;
+
+	printf("Rings:\n");
+	ynl_dump_foreach(rings, dev) {
+		printf("  %8s: ", dev->header.dev_name);
+		if (dev->_present.rx)
+			printf("rx %d ", dev->rx);
+		if (dev->_present.tx)
+			printf("tx %d ", dev->tx);
+		printf("\n");
+	}
+	ethtool_rings_get_list_free(rings);
+
+	ynl_sock_destroy(ys);
+
+	return 0;
+
+err_close:
+	fprintf(stderr, "YNL (%d): %s\n", ys->err.code, ys->err.msg);
+	ynl_sock_destroy(ys);
+	return 2;
+}