tools: ynl: add sample for netdev

Add a sample application using the C library.
My main goal is to make writing selftests easier but until
I have some of those ready I think it's useful to show off
the functionality and let people poke and tinker.

Sample outputs - dump:

$ ./netdev
Select ifc ($ifindex; or 0 = dump; or -2 ntf check): 0
      lo[1]	0:
  enp1s0[2]	23: basic redirect rx-sg

Notifications (watching veth pair getting added and deleted):

$ ./netdev
Select ifc ($ifindex; or 0 = dump; or -2 ntf check): -2
[53]	0: (ntf: dev-add-ntf)
[54]	0: (ntf: dev-add-ntf)
[54]	23: basic redirect rx-sg (ntf: dev-change-ntf)
[53]	23: basic redirect rx-sg (ntf: dev-change-ntf)
[53]	23: basic redirect rx-sg (ntf: dev-del-ntf)
[54]	23: basic redirect rx-sg (ntf: dev-del-ntf)

Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/samples/.gitignore

@@ -0,0 +1 @@
+netdev

tools/net/ynl/samples/Makefile

@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CC=gcc
+CFLAGS=-std=gnu11 -O2 -W -Wall -Wextra -Wno-unused-parameter -Wshadow \
+	-I../lib/ -I../generated/
+ifeq ("$(DEBUG)","1")
+  CFLAGS += -g -fsanitize=address -fsanitize=leak -static-libasan
+endif
+
+LDLIBS=-lmnl ../lib/ynl.a ../generated/protos.a
+
+SRCS=$(wildcard *.c)
+BINS=$(patsubst %.c,%,${SRCS})
+
+include $(wildcard *.d)
+
+all: $(BINS)
+
+$(BINS): ../lib/ynl.a ../generated/protos.a
+
+clean:
+	rm -f *.o *.d *~
+
+hardclean: clean
+	rm -f $(BINS)
+
+.PHONY: all clean
+.DEFAULT_GOAL=all

tools/net/ynl/samples/netdev.c

@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <string.h>
+
+#include <ynl.h>
+
+#include <net/if.h>
+
+#include "netdev-user.h"
+
+/* netdev genetlink family code sample
+ * This sample shows off basics of the netdev family but also notification
+ * handling, hence the somewhat odd UI. We subscribe to notifications first
+ * then wait for ifc selection, so the socket may already accumulate
+ * notifications as we wait. This allows us to test that YNL can handle
+ * requests and notifications getting interleaved.
+ */
+
+static void netdev_print_device(struct netdev_dev_get_rsp *d, unsigned int op)
+{
+	char ifname[IF_NAMESIZE];
+	const char *name;
+
+	if (!d->_present.ifindex)
+		return;
+
+	name = if_indextoname(d->ifindex, ifname);
+	if (name)
+		printf("%8s", name);
+	printf("[%d]\t", d->ifindex);
+
+	if (!d->_present.xdp_features)
+		return;
+
+	printf("%llx:", d->xdp_features);
+	for (int i = 0; d->xdp_features > 1U << i; i++) {
+		if (d->xdp_features & (1U << i))
+			printf(" %s", netdev_xdp_act_str(1 << i));
+	}
+
+	name = netdev_op_str(op);
+	if (name)
+		printf(" (ntf: %s)", name);
+	printf("\n");
+}
+
+int main(int argc, char **argv)
+{
+	struct netdev_dev_get_list *devs;
+	struct ynl_ntf_base_type *ntf;
+	struct ynl_error yerr;
+	struct ynl_sock *ys;
+	int ifindex = 0;
+
+	if (argc > 1)
+		ifindex = strtol(argv[1], NULL, 0);
+
+	ys = ynl_sock_create(&ynl_netdev_family, &yerr);
+	if (!ys) {
+		fprintf(stderr, "YNL: %s\n", yerr.msg);
+		return 1;
+	}
+
+	if (ynl_subscribe(ys, "mgmt"))
+		goto err_close;
+
+	printf("Select ifc ($ifindex; or 0 = dump; or -2 ntf check): ");
+	scanf("%d", &ifindex);
+
+	if (ifindex > 0) {
+		struct netdev_dev_get_req *req;
+		struct netdev_dev_get_rsp *d;
+
+		req = netdev_dev_get_req_alloc();
+		netdev_dev_get_req_set_ifindex(req, ifindex);
+
+		d = netdev_dev_get(ys, req);
+		netdev_dev_get_req_free(req);
+		if (!d)
+			goto err_close;
+
+		netdev_print_device(d, 0);
+		netdev_dev_get_rsp_free(d);
+	} else if (!ifindex) {
+		devs = netdev_dev_get_dump(ys);
+		if (!devs)
+			goto err_close;
+
+		ynl_dump_foreach(devs, d)
+			netdev_print_device(d, 0);
+		netdev_dev_get_list_free(devs);
+	} else if (ifindex == -2) {
+		ynl_ntf_check(ys);
+	}
+	while ((ntf = ynl_ntf_dequeue(ys))) {
+		netdev_print_device((struct netdev_dev_get_rsp *)&ntf->data,
+				    ntf->cmd);
+		ynl_ntf_free(ntf);
+	}
+
+	ynl_sock_destroy(ys);
+	return 0;
+
+err_close:
+	fprintf(stderr, "YNL: %s\n", ys->err.msg);
+	ynl_sock_destroy(ys);
+	return 2;
+}