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

[Martin KaFai Lau <martin.lau@linux.dev>]

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?