[PATCH 2/2] libbpf: Add ring__consume_max / ring_buffer__consume_max

[Andrea Righi]

Introduce a new API to consume items from a ring buffer, limited to a
specified amount, and return to the caller the actual number of items
consumed.

Link: https://lore.kernel.org/lkml/20240310154726.734289-1-andrea.righi@xxxxxxxxxxxxx/T
Signed-off-by: Andrea Righi <andrea.righi@xxxxxxxxxxxxx>
---
 tools/lib/bpf/libbpf.h   | 13 +++++++++++++
 tools/lib/bpf/libbpf.map |  2 ++
 tools/lib/bpf/ringbuf.c  | 35 +++++++++++++++++++++++++++++++++--
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index f88ab50c0229..85161889efd4 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1293,6 +1293,8 @@ LIBBPF_API int ring_buffer__add(struct ring_buffer *rb, int map_fd,
 				ring_buffer_sample_fn sample_cb, void *ctx);
 LIBBPF_API int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms);
 LIBBPF_API int ring_buffer__consume(struct ring_buffer *rb);
+LIBBPF_API int ring_buffer__consume_max(struct ring_buffer *rb,
+					size_t max_items);
 LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
 
 /**
@@ -1367,6 +1369,17 @@ LIBBPF_API int ring__map_fd(const struct ring *r);
  */
 LIBBPF_API int ring__consume(struct ring *r);
 
+/**
+ * @brief **ring__consume_max()** consumes up to a certain amount of items from
+ * a ringbuffer without event polling.
+ *
+ * @param r A ringbuffer object.
+ * @param max_items Maximum amount of items to consume.
+ * @return The number of items consumed (or max_items, whichever is less), or a
+ * negative number if any of the callbacks return an error.
+ */
+LIBBPF_API int ring__consume_max(struct ring *r, size_t max_items);
+
 struct user_ring_buffer_opts {
 	size_t sz; /* size of this struct, for forward/backward compatibility */
 };
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 51732ecb1385..bb3ed905119d 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -415,4 +415,6 @@ LIBBPF_1.4.0 {
 		bpf_token_create;
 		btf__new_split;
 		btf_ext__raw_data;
+		ring__consume_max;
+		ring_buffer__consume_max;
 } LIBBPF_1.3.0;
diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index 81df535040d1..c8123e326b1a 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -281,6 +281,32 @@ static int64_t ringbuf_process_ring(struct ring *r, int64_t max_items)
 	return cnt;
 }
 
+/* Consume available ring buffer(s) data without event polling up to max_items.
+ *
+ * Returns number of records consumed across all registered ring buffers (or
+ * max_items, whichever is less), or negative number if any of the callbacks
+ * return error.
+ */
+int ring_buffer__consume_max(struct ring_buffer *rb, size_t max_items)
+{
+	int64_t err, res = 0;
+	int i;
+
+	for (i = 0; i < rb->ring_cnt; i++) {
+		struct ring *ring = rb->rings[i];
+
+		err = ringbuf_process_ring(ring, max_items);
+		if (err < 0)
+			return libbpf_err(err);
+		res += err;
+		max_items -= err;
+
+		if (!max_items)
+			break;
+	}
+	return res;
+}
+
 /* Consume available ring buffer(s) data without event polling.
  * Returns number of records consumed across all registered ring buffers (or
  * INT_MAX, whichever is less), or negative number if any of the callbacks
@@ -376,17 +402,22 @@ int ring__map_fd(const struct ring *r)
 	return r->map_fd;
 }
 
-int ring__consume(struct ring *r)
+int ring__consume_max(struct ring *r, size_t max_items)
 {
 	int64_t res;
 
-	res = ringbuf_process_ring(r, INT_MAX);
+	res = ringbuf_process_ring(r, max_items);
 	if (res < 0)
 		return libbpf_err(res);
 
 	return res;
 }
 
+int ring__consume(struct ring *r)
+{
+	return ring__consume_max(r, INT_MAX);
+}
+
 static void user_ringbuf_unmap_ring(struct user_ring_buffer *rb)
 {
 	if (rb->consumer_pos) {
-- 
2.43.0