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

[Menglong Dong <menglong.dong@linux.dev>]

On 2026/3/20 20:40, Jiri Olsa wrote:
> On Fri, Mar 20, 2026 at 04:41:55PM +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.
> > 
> > Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
> > ---
> >  .../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..c3fa57ec430b 100644
> > --- a/tools/testing/selftests/bpf/progs/map_ptr_kern.c
> > +++ b/tools/testing/selftests/bpf/progs/map_ptr_kern.c
> > @@ -647,21 +647,39 @@ 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 {
> >  	__uint(type, BPF_MAP_TYPE_RINGBUF);
> > +	__uint(max_entries, 1 << 10);
> 
> do you need to set max_entries? there's already check below
> making sure it's 4096

Hi, Jiri. Thanks for the reviewing. You are right, we don't
need to set the max_entries here, as it will be set in the
test_map_ptr(). I'll remove this part in V2.

Thanks!
Menglong Dong

> 
> jirka
> 
> 
> >  } m_ringbuf SEC(".maps");
> >  
> >  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);
> > +	VERIFY(rb->producer_pos == 128 + 8);
> > +
> >  	return 1;
> >  }
> >  
> 
>