selftests/bpf: Add re-attach test to fentry_test

Adding the test to re-attach (detach/attach again) tracing
fentry programs, plus check that already linked program can't
be attached again.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210414195147.1624932-4-jolsa@kernel.org

tools/testing/selftests/bpf/prog_tests/fentry_test.c

@@ -3,35 +3,57 @@
 #include <test_progs.h>
 #include "fentry_test.skel.h"
 
-void test_fentry_test(void)
+static int fentry_test(struct fentry_test *fentry_skel)
 {
-	struct fentry_test *fentry_skel = NULL;
 	int err, prog_fd, i;
 	__u32 duration = 0, retval;
+	struct bpf_link *link;
 	__u64 *result;
 
-	fentry_skel = fentry_test__open_and_load();
-	if (CHECK(!fentry_skel, "fentry_skel_load", "fentry skeleton failed\n"))
-		goto cleanup;
-
 	err = fentry_test__attach(fentry_skel);
-	if (CHECK(err, "fentry_attach", "fentry attach failed: %d\n", err))
-		goto cleanup;
+	if (!ASSERT_OK(err, "fentry_attach"))
+		return err;
+
+	/* Check that already linked program can't be attached again. */
+	link = bpf_program__attach(fentry_skel->progs.test1);
+	if (!ASSERT_ERR_PTR(link, "fentry_attach_link"))
+		return -1;
 
 	prog_fd = bpf_program__fd(fentry_skel->progs.test1);
 	err = bpf_prog_test_run(prog_fd, 1, NULL, 0,
 				NULL, NULL, &retval, &duration);
-	CHECK(err || retval, "test_run",
-	      "err %d errno %d retval %d duration %d\n",
-	      err, errno, retval, duration);
+	ASSERT_OK(err, "test_run");
+	ASSERT_EQ(retval, 0, "test_run");
 
 	result = (__u64 *)fentry_skel->bss;
-	for (i = 0; i < 6; i++) {
-		if (CHECK(result[i] != 1, "result",
-			  "fentry_test%d failed err %lld\n", i + 1, result[i]))
-			goto cleanup;
+	for (i = 0; i < sizeof(*fentry_skel->bss) / sizeof(__u64); i++) {
+		if (!ASSERT_EQ(result[i], 1, "fentry_result"))
+			return -1;
 	}
 
+	fentry_test__detach(fentry_skel);
+
+	/* zero results for re-attach test */
+	memset(fentry_skel->bss, 0, sizeof(*fentry_skel->bss));
+	return 0;
+}
+
+void test_fentry_test(void)
+{
+	struct fentry_test *fentry_skel = NULL;
+	int err;
+
+	fentry_skel = fentry_test__open_and_load();
+	if (!ASSERT_OK_PTR(fentry_skel, "fentry_skel_load"))
+		goto cleanup;
+
+	err = fentry_test(fentry_skel);
+	if (!ASSERT_OK(err, "fentry_first_attach"))
+		goto cleanup;
+
+	err = fentry_test(fentry_skel);
+	ASSERT_OK(err, "fentry_second_attach");
+
 cleanup:
 	fentry_test__destroy(fentry_skel);
 }