[PATCH bpf-next v3] selftests/bpf: test access to ringbuf position with map pointer

[Menglong Dong]

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 + 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@xxxxxxxxxxxxxxx>
Reviewed-by: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
v3:
- use BPF_RINGBUF_HDR_SZ instead of 8 in check_ringbuf()

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  | 17 +++++++++++++++++
 1 file changed, 17 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..373c8d17ea55 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 +665,20 @@ 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 + BPF_RINGBUF_HDR_SZ);
+
 	return 1;
 }
 
-- 
2.53.0