linux-kernel - [PATCH] libbpf: ringbuf: allow to partially consume items

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Date: Sun, 10 Mar 2024 16:47:26 +0100
From: Andrea Righi <andrea.righi@...onical.com>
To: Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	David Vernet <void@...ifault.com>,
	Tejun Heo <tj@...nel.org>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Andrea Righi <andrea.righi@...onical.com>
Subject: [PATCH] libbpf: ringbuf: allow to partially consume items

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@...onical.com>
---
 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