selftests: nl_netdev: add a trivial Netlink netdev test

Add a trivial test using YNL.

$ ./tools/testing/selftests/net/nl_netdev.py
KTAP version 1
1..2
ok 1 nl_netdev.empty_check
ok 2 nl_netdev.lo_check

Instantiate the family once, it takes longer than the test itself.

Reviewed-by: Petr Machata <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/testing/selftests/net/Makefile

···
 TEST_PROGS += cmsg_so_mark.sh
 TEST_PROGS += cmsg_time.sh cmsg_ipv6.sh
 TEST_PROGS += netns-name.sh
+TEST_PROGS += nl_netdev.py
 TEST_PROGS += srv6_end_dt46_l3vpn_test.sh
 TEST_PROGS += srv6_end_dt4_l3vpn_test.sh
 TEST_PROGS += srv6_end_dt6_l3vpn_test.sh

tools/testing/selftests/net/nl_netdev.py

···
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+from lib.py import ksft_run, ksft_pr, ksft_eq, ksft_ge, NetdevFamily
+
+
+def empty_check(nf) -> None:
+    devs = nf.dev_get({}, dump=True)
+    ksft_ge(len(devs), 1)
+
+
+def lo_check(nf) -> None:
+    lo_info = nf.dev_get({"ifindex": 1})
+    ksft_eq(len(lo_info['xdp-features']), 0)
+    ksft_eq(len(lo_info['xdp-rx-metadata-features']), 0)
+
+
+def main() -> None:
+    nf = NetdevFamily()
+    ksft_run([empty_check, lo_check], args=(nf, ))
+
+
+if __name__ == "__main__":
+    main()