Re: [PATCH v1 2/7] bpf: Add bpf_perf_event_aux_pause kfunc

[Yonghong Song <yonghong.song@linux.dev>]

On 7/14/25 10:45 AM, Leo Yan wrote:
> Hi Yonghong,
>
> Really sorry for the long delay. Now I am restarting this work.
>
> On Mon, Dec 16, 2024 at 09:21:15AM -0800, Yonghong Song wrote:
>> On 12/15/24 11:34 AM, Leo Yan wrote:
>>> The bpf_perf_event_aux_pause kfunc will be used to control the Perf AUX
>>> area to pause or resume.
>>>
>>> An example use-case is attaching eBPF to Ftrace tracepoints.  When a
>>> tracepoint is hit, the associated eBPF program will be executed.  The
>>> eBPF program can invoke bpf_perf_event_aux_pause() to pause or resume
>>> AUX trace.  This is useful for fine-grained tracing by combining
>>> Perf and eBPF.
>>>
>>> This commit implements the bpf_perf_event_aux_pause kfunc, and make it
>>> pass the eBPF verifier.
>> The subject and commit message mentions to implement a kfunc,
>> but actually you implemented a uapi helper. Please implement a kfunc
>> instead (searching __bpf_kfunc in kernel/bpf directory).
> After some research, my understanding is that kfunc is flexible for
> exposing APIs via BTF, whereas BPF_CALL is typically used for core BPF
> features - such as accessing BPF maps.
>
> Coming back to this patch: it exposes a function with the following
> definition:
>
>    int bpf_perf_event_aux_pause(struct bpf_map *map, u64 flags, u32 pause);
>
> I'm not certain whether using __bpf_kfunc is appropriate here, or if I
> should stick to BPF_CALL to ensure support for accessing bpf_map
> pointers?

Using helpers (BPF_CALL) is not an option as the whole bpf ecosystem
moves to kfunc mechanism. You can certainly use kfunc with 'struct bpf_map *'
as the argument. For example the following kfunc:
   __bpf_kfunc s64 bpf_map_sum_elem_count(const struct bpf_map *map)
in kernel/bpf/map_iter.c
   

>
> Thanks,
> Leo