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

From: Andrea Righi <andrea.righi@canonical.com>
To: Andrii Nakryiko <andrii@kernel.org>,
	Eduard Zingerman <eddyz87@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>,
	Yonghong Song <yonghong.song@linux.dev>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>, David Vernet <void@manifault.com>,
	Tejun Heo <tj@kernel.org>,
	bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
	Andrea Righi <andrea.righi@canonical.com>
Subject: [PATCH] libbpf: ringbuf: allow to partially consume items
Date: Sun, 10 Mar 2024 16:47:26 +0100	[thread overview]
Message-ID: <20240310154726.734289-1-andrea.righi@canonical.com> (raw)

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@canonical.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

