Re: [PATCH bpf-next v2] selftests/bpf: test access to ringbuf position with map pointer

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Mar 23, 2026 at 10:18:39AM +0800, Menglong Dong wrote:
> Add the testing to access the bpf_ringbuf with the map pointer.
> "consumer_pos" and "producer_pos" is accessed in this testing. We reserve
> 128 bytes in the ringbuf to test the producer_pos, which should be
> "128 + 8", and the "8" is BPF_RINGBUF_HDR_SZ.
> 
> It will be helpful if we want to evaluate the usage of the ringbuf in bpf
> prog with the consumer and producer position.

lgtm, question though.. is this related to some kernel change or
some ongoing work? looks like basic operation that's already
tested indirectly by existing tests

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> 
> Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
> ---
> v2:
> - don't set the max_entries for the ringbuf map
> - add comment for the producer_pos
> ---
>  .../testing/selftests/bpf/progs/map_ptr_kern.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/progs/map_ptr_kern.c b/tools/testing/selftests/bpf/progs/map_ptr_kern.c
> index efaf622c28dd..d7611e7018ca 100644
> --- a/tools/testing/selftests/bpf/progs/map_ptr_kern.c
> +++ b/tools/testing/selftests/bpf/progs/map_ptr_kern.c
> @@ -647,8 +647,14 @@ static inline int check_devmap_hash(void)
>  	return 1;
>  }
>  
> +struct bpf_ringbuf {
> +	unsigned long consumer_pos;
> +	unsigned long producer_pos;
> +} __attribute__((preserve_access_index));
> +
>  struct bpf_ringbuf_map {
>  	struct bpf_map map;
> +	struct bpf_ringbuf *rb;
>  } __attribute__((preserve_access_index));
>  
>  struct {
> @@ -659,9 +665,21 @@ static inline int check_ringbuf(void)
>  {
>  	struct bpf_ringbuf_map *ringbuf = (struct bpf_ringbuf_map *)&m_ringbuf;
>  	struct bpf_map *map = (struct bpf_map *)&m_ringbuf;
> +	struct bpf_ringbuf *rb;
> +	void *ptr;
>  
>  	VERIFY(check(&ringbuf->map, map, 0, 0, page_size));
>  
> +	ptr = bpf_ringbuf_reserve(&m_ringbuf, 128, 0);
> +	VERIFY(ptr);
> +
> +	bpf_ringbuf_discard(ptr, 0);
> +	rb = ringbuf->rb;
> +	VERIFY(rb);
> +	VERIFY(rb->consumer_pos == 0);
> +	/* The "8" here is BPF_RINGBUF_HDR_SZ */
> +	VERIFY(rb->producer_pos == 128 + 8);
> +
>  	return 1;
>  }
>  
> -- 
> 2.53.0
>