Re: [PATCH bpf-next v4 1/6] selftests/bpf: Add traffic monitor functions.

[Kui-Feng Lee <sinquersw@gmail.com>]

On 8/6/24 15:22, Martin KaFai Lau wrote:
> On 8/6/24 3:07 PM, Kui-Feng Lee wrote:
>>
>>
>> On 8/1/24 21:35, Kui-Feng Lee wrote:
>>>
>>>
>>> On 8/1/24 20:43, Martin KaFai Lau wrote:
>>>> On 7/31/24 12:31 PM, Kui-Feng Lee wrote:
>>>>> diff --git a/tools/testing/selftests/bpf/test_progs.h 
>>>>> b/tools/testing/ selftests/bpf/test_progs.h
>>>>> index cb9d6d46826b..5d4e61fa26a1 100644
>>>>> --- a/tools/testing/selftests/bpf/test_progs.h
>>>>> +++ b/tools/testing/selftests/bpf/test_progs.h
>>>>> @@ -473,4 +473,20 @@ extern void test_loader_fini(struct 
>>>>> test_loader *tester);
>>>>>       test_loader_fini(&tester);                           \
>>>>>   })
>>>>> +struct tmonitor_ctx;
>>>>> +
>>>>> +#ifdef TRAFFIC_MONITOR
>>>>> +struct tmonitor_ctx *traffic_monitor_start(const char *netns);
>>>>> +void traffic_monitor_stop(struct tmonitor_ctx *ctx);
>>>>> +#else
>>>>> +static inline struct tmonitor_ctx *traffic_monitor_start(const 
>>>>> char *netns)
>>>>> +{
>>>>> +    return (struct tmonitor_ctx *)-1;
>>>>
>>>> hmm... from peeking patch 3, only NULL is checked.
>>
>> When traffic monitor is disable, these two functions are noop.
>> Returning -1 (not NULL) is convenient for the callers. They don't need
>> to tell if the error caused by a real error or by the disabled
>> feature.
> 
> I pasted the code from patch 3 here only to ensure I understand the 
> above explanation correctly:
> 
> +        netns_obj->tmon = traffic_monitor_start(name);
> +        if (!netns_obj->tmon)
>              ^^^^^^^^^^^^^^^^
> 
> +            goto fail;
> 
> Does it mean the traffic_monitor_start() above will never be called if 
> TRAFFIC_MONITOR macro is not defined such that traffic_monitor_start() 
> returning -1 but testing for NULL here does not matter?

Correct!