Re: [PATCH bpf-next 6/9] selftests/bpf: Verify tracing link_create logs

[Leon Hwang]

On 2026/11/9 22:47, bot+bpf-ci@xxxxxxxxxx wrote:
>> selftests/bpf: Verify tracing link_create logs
> 
> TL;DR: Test issue: the invalid attach_type subtest in tracing_link.c may fail
> earlier in the generic check, so it may not exercise the new tracing log.
> Using BPF_TRACE_FEXIT on the fentry program might fix it.
> 
>> diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_link.c b/tools/testing/selftests/bpf/prog_tests/tracing_link.c
>> new file mode 100644
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/prog_tests/tracing_link.c
> 
> [ ... ]
> 
>> +static void test_log_invalid_attach_type(void)
>> +{
>> +	const char *msg = "Invalid attach_type.\n";
>> +
>> +	test_fentry_link_create_log(0, 0, 0, BPF_XDP, false, msg);
>> +}
> 
> Does this subtest reach the tracing-specific log added by "bpf: Add log
> support for tracing link_create"?
> 
> With BPF_XDP on the fentry program, link_create() fails earlier in the
> generic check:
> 
>     ret = bpf_prog_attach_check_attach_type(prog, attr->link_create.attach_type);
>     if (ret) {
>         bpf_log(log, "Invalid attach_type.\n");
>         goto out;
>     }
> 
> For BPF_PROG_TYPE_TRACING, attach_type_to_prog_type(BPF_XDP) returns
> BPF_PROG_TYPE_XDP, so bpf_prog_attach_check_attach_type() returns -EINVAL
> and the case below is never reached:
> 
>     case BPF_PROG_TYPE_TRACING:
>         if (attr->link_create.attach_type != prog->expected_attach_type) {
>             bpf_log(log, "Invalid attach_type.\n");
> 
> Both messages are identical, so this subtest would still pass if the
> tracing-branch bpf_log() were removed.  The generic check is already
> covered by the invalid_attach_type subtest in xdp_link.c.
> 
> Would passing an attach type that maps to BPF_PROG_TYPE_TRACING but
> differs from the program's expected_attach_type, for example
> BPF_TRACE_FEXIT for this fentry program, exercise the new log instead?
> 

Agreed.

Will change the log msg to "Invalid tracing attach_type.\n", and change
BPF_XDP to BPF_TRACE_FEXIT.

Thanks,
Leon