selftests/bpf: add offload test based on netdevsim

Add a test of BPF offload control path interfaces based on
just-added netdevsim driver.  Perform various checks of both
the stack and the expected driver behaviour.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/Makefile

@@ -17,9 +17,10 @@ TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map test
 
 TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test_obj_id.o \
 	test_pkt_md_access.o test_xdp_redirect.o test_xdp_meta.o sockmap_parse_prog.o     \
-	sockmap_verdict_prog.o dev_cgroup.o
+	sockmap_verdict_prog.o dev_cgroup.o sample_ret0.o
 
-TEST_PROGS := test_kmod.sh test_xdp_redirect.sh test_xdp_meta.sh
+TEST_PROGS := test_kmod.sh test_xdp_redirect.sh test_xdp_meta.sh \
+	test_offload.py
 
 include ../lib.mk
 

tools/testing/selftests/bpf/sample_ret0.c

@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) */
+
+/* Sample program which should always load for testing control paths. */
+int func()
+{
+	return 0;
+}