selftests/bpf: add pre bpf_prog_test_run_opts() callback for test_loader

When a test case is annotated with __retval tag the test_loader engine
would use libbpf's bpf_prog_test_run_opts() to do a test run of the
program and compare retvals.

This commit allows to perform arbitrary actions on bpf object right
before test loader invokes bpf_prog_test_run_opts(). This could be
used to setup some state for program execution, e.g. fill some maps.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230420232317.2181776-4-eddyz87@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/test_loader.c

@@ -590,6 +590,14 @@ void run_subtest(struct test_loader *tester,
 		if (restore_capabilities(&caps))
 			goto tobj_cleanup;
 
+		if (tester->pre_execution_cb) {
+			err = tester->pre_execution_cb(tobj);
+			if (err) {
+				PRINT_FAIL("pre_execution_cb failed: %d\n", err);
+				goto tobj_cleanup;
+			}
+		}
+
 		do_prog_test_run(bpf_program__fd(tprog), &retval);
 		if (retval != subspec->retval && subspec->retval != POINTER_VALUE) {
 			PRINT_FAIL("Unexpected retval: %d != %d\n", retval, subspec->retval);

tools/testing/selftests/bpf/test_progs.h

@@ -424,14 +424,23 @@ int get_bpf_max_tramp_links(void);
 
 #define BPF_TESTMOD_TEST_FILE "/sys/kernel/bpf_testmod"
 
+typedef int (*pre_execution_cb)(struct bpf_object *obj);
+
 struct test_loader {
 	char *log_buf;
 	size_t log_buf_sz;
 	size_t next_match_pos;
+	pre_execution_cb pre_execution_cb;
 
 	struct bpf_object *obj;
 };
 
+static inline void test_loader__set_pre_execution_cb(struct test_loader *tester,
+						     pre_execution_cb cb)
+{
+	tester->pre_execution_cb = cb;
+}
+
 typedef const void *(*skel_elf_bytes_fn)(size_t *sz);
 
 extern void test_loader__run_subtests(struct test_loader *tester,