netdev - Re: [PATCH v5 bpf-next 3/3] selftests/bpf: add raw_tp_test

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Date:   Fri, 25 Sep 2020 03:01:43 +0000
From:   Song Liu <songliubraving@...com>
To:     John Fastabend <john.fastabend@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "kpsingh@...omium.org" <kpsingh@...omium.org>
Subject: Re: [PATCH v5 bpf-next 3/3] selftests/bpf: add raw_tp_test_run



> On Sep 24, 2020, at 6:01 PM, John Fastabend <john.fastabend@...il.com> wrote:
> 
> Song Liu wrote:
>> This test runs test_run for raw_tracepoint program. The test covers ctx
>> input, retval output, and running on correct cpu.
>> 
>> Signed-off-by: Song Liu <songliubraving@...com>
>> ---
> 
> [...]
> 
>> +void test_raw_tp_test_run(void)
>> +{
>> +	struct bpf_prog_test_run_attr test_attr = {};
>> +	int comm_fd = -1, err, nr_online, i, prog_fd;
>> +	__u64 args[2] = {0x1234ULL, 0x5678ULL};
>> +	int expected_retval = 0x1234 + 0x5678;
>> +	struct test_raw_tp_test_run *skel;
>> +	char buf[] = "new_name";
>> +	bool *online = NULL;
>> +
>> +	err = parse_cpu_mask_file("/sys/devices/system/cpu/online", &online,
>> +				  &nr_online);
>> +	if (CHECK(err, "parse_cpu_mask_file", "err %d\n", err))
>> +		return;
>> +
>> +	skel = test_raw_tp_test_run__open_and_load();
>> +	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
>> +		goto cleanup;
>> +
>> +	err = test_raw_tp_test_run__attach(skel);
>> +	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
>> +		goto cleanup;
>> +
>> +	comm_fd = open("/proc/self/comm", O_WRONLY|O_TRUNC);
>> +	if (CHECK(comm_fd < 0, "open /proc/self/comm", "err %d\n", errno))
>> +		goto cleanup;
>> +
>> +	err = write(comm_fd, buf, sizeof(buf));
>> +	CHECK(err < 0, "task rename", "err %d", errno);
>> +
>> +	CHECK(skel->bss->count == 0, "check_count", "didn't increase\n");
>> +	CHECK(skel->data->on_cpu != 0xffffffff, "check_on_cpu", "got wrong value\n");
>> +
>> +	prog_fd = bpf_program__fd(skel->progs.rename);
>> +	test_attr.prog_fd = prog_fd;
>> +	test_attr.ctx_in = args;
>> +	test_attr.ctx_size_in = sizeof(__u64);
>> +
>> +	err = bpf_prog_test_run_xattr(&test_attr);
>> +	CHECK(err == 0, "test_run", "should fail for too small ctx\n");
>> +
>> +	test_attr.ctx_size_in = sizeof(args);
>> +	err = bpf_prog_test_run_xattr(&test_attr);
>> +	CHECK(err < 0, "test_run", "err %d\n", errno);
>> +	CHECK(test_attr.retval != expected_retval, "check_retval",
>> +	      "expect 0x%x, got 0x%x\n", expected_retval, test_attr.retval);
>> +
>> +	for (i = 0; i < nr_online; i++) {
>> +		if (online[i]) {
>> +			DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,
>> +				.ctx_in = args,
>> +				.ctx_size_in = sizeof(args),
>> +				.flags = BPF_F_TEST_RUN_ON_CPU,
>> +				.retval = 0,
>> +				.cpu = i,
>> +			);
>> +
>> +			err = bpf_prog_test_run_opts(prog_fd, &opts);
>> +			CHECK(err < 0, "test_run_opts", "err %d\n", errno);
>> +			CHECK(skel->data->on_cpu != i, "check_on_cpu",
>> +			      "expect %d got %d\n", i, skel->data->on_cpu);
>> +			CHECK(opts.retval != expected_retval,
>> +			      "check_retval", "expect 0x%x, got 0x%x\n",
>> +			      expected_retval, opts.retval);
>> +
>> +			if (i == 0) {
>> +				/* invalid cpu ID should fail with ENXIO */
>> +				opts.cpu = 0xffffffff;
>> +				err = bpf_prog_test_run_opts(prog_fd, &opts);
>> +				CHECK(err != -1 || errno != ENXIO,
>> +				      "test_run_opts_fail",
>> +				      "should failed with ENXIO\n");
>> +			} else {
> 
> One more request...
> 
> How about pull this if/else branch out of the for loop here? It feels a bit
> clumsy as-is imo. Also is it worthwhile to bang on the else branch for evey
> cpu I would think testing for any non-zero value should be sufficient.

I thought about both these two directions. The biggest benefit of current
version is that we can reuse the DECLARE_LIBBPF_OPTS() in this loop. Moving
it to the beginning of the function bothers me a little bit.. 

Thanks,
Song