[PATCH] libbpf: ringbuf: allow to partially consume items

[Andrea Righi]

Instead of always consuming all items from a ring buffer in a greedy
way, allow to stop when the callback returns a value > 0.

This allows to distinguish between an error condition and an intentional
stop condition by returning a non-negative non-zero value from the ring
buffer callback.

This can be useful, for example, to consume just a single item from the
ring buffer.

Signed-off-by: Andrea Righi <andrea.righi@xxxxxxxxxxxxx>
---
 tools/lib/bpf/ringbuf.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index aacb64278a01..dd8908eb3204 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -265,6 +265,14 @@ static int64_t ringbuf_process_ring(struct ring *r)
 					return err;
 				}
 				cnt++;
+				if (err > 0) {
+					/* update consumer pos and return the
+					 * total amount of items consumed.
+					 */
+					smp_store_release(r->consumer_pos,
+							  cons_pos);
+					goto done;
+				}
 			}
 
 			smp_store_release(r->consumer_pos, cons_pos);
-- 
2.43.0