Add a sample application for wireguard, using the generated C library,

The main benefit of this is to exercise the generated library,
which might be useful for future selftests.

In order to support usage with a pre-YNL wireguard.h in /usr/include,
then the former guard is added to Makefile.deps as well.

Example:
  $ make -C tools/net/ynl/lib
  $ make -C tools/net/ynl/generated
  $ make -C tools/net/ynl/samples wireguard
  $ ./tools/net/ynl/samples/wireguard
  usage: ./tools/net/ynl/samples/wireguard <ifindex|ifname>
  $ sudo ./tools/net/ynl/samples/wireguard wg-test
  Interface 3: wg-test
      Peer 6adfb183a4a2c94a2f92dab5ade762a4788[...]:
          Data: rx: 42 / tx: 42 bytes
          Allowed IPs:
              0.0.0.0/0
              ::/0

Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
---
 MAINTAINERS                       |   1 +
 tools/net/ynl/Makefile.deps       |   2 +
 tools/net/ynl/samples/.gitignore  |   1 +
 tools/net/ynl/samples/wireguard.c | 104 ++++++++++++++++++++++++++++++
 4 files changed, 108 insertions(+)
 create mode 100644 tools/net/ynl/samples/wireguard.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 35cd289899f7..1c9c21ff2c97 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27651,6 +27651,7 @@ L:	netdev@vger.kernel.org
 S:	Maintained
 F:	Documentation/netlink/specs/wireguard.yaml
 F:	drivers/net/wireguard/
+F:	tools/net/ynl/samples/wireguard.c
 F:	tools/testing/selftests/wireguard/
 
 WISTRON LAPTOP BUTTON DRIVER
diff --git a/tools/net/ynl/Makefile.deps b/tools/net/ynl/Makefile.deps
index 865fd2e8519e..a9a5348b31a3 100644
--- a/tools/net/ynl/Makefile.deps
+++ b/tools/net/ynl/Makefile.deps
@@ -48,3 +48,5 @@ CFLAGS_tc:= $(call get_hdr_inc,__LINUX_RTNETLINK_H,rtnetlink.h) \
 	$(call get_hdr_inc,_TC_SKBEDIT_H,tc_act/tc_skbedit.h) \
 	$(call get_hdr_inc,_TC_TUNNEL_KEY_H,tc_act/tc_tunnel_key.h)
 CFLAGS_tcp_metrics:=$(call get_hdr_inc,_LINUX_TCP_METRICS_H,tcp_metrics.h)
+CFLAGS_wireguard:=$(call get_hdr_inc,_LINUX_WIREGUARD_H,wireguard.h) \
+	-D _WG_UAPI_WIREGUARD_H # alternate pre-YNL guard
diff --git a/tools/net/ynl/samples/.gitignore b/tools/net/ynl/samples/.gitignore
index 7f5fca7682d7..09c61e4c18cd 100644
--- a/tools/net/ynl/samples/.gitignore
+++ b/tools/net/ynl/samples/.gitignore
@@ -7,3 +7,4 @@ rt-addr
 rt-link
 rt-route
 tc
+wireguard
diff --git a/tools/net/ynl/samples/wireguard.c b/tools/net/ynl/samples/wireguard.c
new file mode 100644
index 000000000000..43f3551eb101
--- /dev/null
+++ b/tools/net/ynl/samples/wireguard.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <arpa/inet.h>
+#include <string.h>
+#include <stdio.h>
+#include <errno.h>
+#include <ynl.h>
+
+#include "wireguard-user.h"
+
+static void print_allowed_ip(const struct wireguard_wgallowedip *aip)
+{
+	char addr_out[INET6_ADDRSTRLEN];
+
+	if (!inet_ntop(aip->family, aip->ipaddr, addr_out, sizeof(addr_out))) {
+		addr_out[0] = '?';
+		addr_out[1] = '\0';
+	}
+	printf("\t\t\t%s/%u\n", addr_out, aip->cidr_mask);
+}
+
+/* Only printing public key in this demo. For better key formatting,
+ * use the constant-time implementation as found in wireguard-tools.
+ */
+static void print_peer_header(const struct wireguard_wgpeer *peer)
+{
+	unsigned int i;
+	uint8_t *key = peer->public_key;
+	unsigned int len = peer->_len.public_key;
+
+	if (len != 32)
+		return;
+	printf("\tPeer ");
+	for (i = 0; i < len; i++)
+		printf("%02x", key[i]);
+	printf(":\n");
+}
+
+static void print_peer(const struct wireguard_wgpeer *peer)
+{
+	unsigned int i;
+
+	print_peer_header(peer);
+	printf("\t\tData: rx: %llu / tx: %llu bytes\n",
+	       peer->rx_bytes, peer->tx_bytes);
+	printf("\t\tAllowed IPs:\n");
+	for (i = 0; i < peer->_count.allowedips; i++)
+		print_allowed_ip(&peer->allowedips[i]);
+}
+
+static void build_request(struct wireguard_get_device_req *req, char *arg)
+{
+	char *endptr;
+	int ifindex;
+
+	ifindex = strtol(arg, &endptr, 0);
+	if (endptr != arg + strlen(arg) || errno != 0)
+		ifindex = 0;
+	if (ifindex > 0)
+		wireguard_get_device_req_set_ifindex(req, ifindex);
+	else
+		wireguard_get_device_req_set_ifname(req, arg);
+}
+
+int main(int argc, char **argv)
+{
+	struct wireguard_get_device_list *devs;
+	struct wireguard_get_device_req *req;
+	struct ynl_sock *ys;
+
+	if (argc < 2) {
+		fprintf(stderr, "usage: %s <ifindex|ifname>\n", argv[0]);
+		return 1;
+	}
+
+	req = wireguard_get_device_req_alloc();
+	build_request(req, argv[1]);
+
+	ys = ynl_sock_create(&ynl_wireguard_family, NULL);
+	if (!ys)
+		return 2;
+
+	devs = wireguard_get_device_dump(ys, req);
+	if (!devs)
+		goto err_close;
+
+	ynl_dump_foreach(devs, d) {
+		unsigned int i;
+
+		printf("Interface %d: %s\n", d->ifindex, d->ifname);
+		for (i = 0; i < d->_count.peers; i++)
+			print_peer(&d->peers[i]);
+	}
+	wireguard_get_device_list_free(devs);
+	wireguard_get_device_req_free(req);
+	ynl_sock_destroy(ys);
+
+	return 0;
+
+err_close:
+	fprintf(stderr, "YNL (%d): %s\n", ys->err.code, ys->err.msg);
+	wireguard_get_device_req_free(req);
+	ynl_sock_destroy(ys);
+	return 3;
+}
-- 
2.51.0

On Wed, Nov 05, 2025 at 06:32:17PM +0000, Asbjørn Sloth Tønnesen wrote:
> +CFLAGS_wireguard:=$(call get_hdr_inc,_LINUX_WIREGUARD_H,wireguard.h) \
> +	-D _WG_UAPI_WIREGUARD_H # alternate pre-YNL guard

I don't totally grok what's going on here. As I understand it, this
makefile creates `wireguard-user.h` in the generated/ include path,
which has all the various netlink wrapper declarations. And then this
also references, somehow, include/uapi/linux/wireguard.h, for the constants.
For some reason, you're then defining _WG_UAPI_WIREGUARD_H here, so that
wireguard.h from /usr/include doesn't clash. But also, why would it?
Isn't this just a matter of placing $(src)/include/uapi earlier in the
include file path?

Jason

On 11/18/25 3:20 PM, Jason A. Donenfeld wrote:
> On Wed, Nov 05, 2025 at 06:32:17PM +0000, Asbjørn Sloth Tønnesen wrote:
>> +CFLAGS_wireguard:=$(call get_hdr_inc,_LINUX_WIREGUARD_H,wireguard.h) \
>> +	-D _WG_UAPI_WIREGUARD_H # alternate pre-YNL guard
> 
> I don't totally grok what's going on here. As I understand it, this
> makefile creates `wireguard-user.h` in the generated/ include path,
> which has all the various netlink wrapper declarations. And then this
> also references, somehow, include/uapi/linux/wireguard.h, for the constants.
> For some reason, you're then defining _WG_UAPI_WIREGUARD_H here, so that
> wireguard.h from /usr/include doesn't clash. But also, why would it?
> Isn't this just a matter of placing $(src)/include/uapi earlier in the
> include file path?

The aim is to use the generated in-tree header, while avoiding making a
copy, and avoiding the system header.

As an example then in tools/net/ynl/generated/Makefile:

%-user.o: %-user.c %-user.h
         @echo -e "\tCC $@"
         @$(COMPILE.c) $(CFLAGS_$*) -o $@ $<

Where for the "wireguard-user.o" target, then "$(CFLAGS_$*)" expands to
"$CFLAGS_wireguard".

CFLAGS_wireguard has two parts the normal one similar to the other families,
and a transitional extra guard.

The header guard in the old UAPI header is "_WG_UAPI_WIREGUARD_H".
The header guard in the new UAPI header in-tree is "_UAPI_LINUX_WIREGUARD_H".
The header guard in the new UAPI header in-system is "_LINUX_WIREGUARD_H".

Linux uapi headers are installed using scripts/headers_install.sh, which
transforms the headers slightly, one of these transformations is to alter
the header guard, stripping the _UAPI in the beginning of the guard.

So "get_hdr_inc=-D$(1) -include $(UAPI_PATH)/linux/$(2)" does:
1) Defines the in-system guard
2) Includes the in-tree header

The purpose of defining the in-system guard is disable the include in
the code, as it's header guard is already defined.

I added the extra transitional define of the old UAPI guard, so that
it also works on systems with the old header installed in /usr.
This extra line can be removed in a few releases, when we don't care
about compiling these tools on a system with the old header installed.

On Tue, Nov 18, 2025 at 6:16 PM Asbjørn Sloth Tønnesen <ast@fiberby.net> wrote:
> This extra line can be removed in a few releases, when we don't care
> about compiling these tools on a system with the old header installed.

Sounds good. I'll put this on my calendar to revisit in 6 months.

Jason