linux-kernel - [PATCH bpf-next v4] libbpf: Expose API to consume one ring at a time

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Date:   Thu, 27 Jul 2023 10:34:38 +0200
From:   Adam Sindelar <adam@...signal.io>
To:     bpf@...r.kernel.org
Cc:     Adam Sindelar <ats@...com>, David Vernet <void@...ifault.com>,
        Brendan Jackman <jackmanb@...gle.com>,
        KP Singh <kpsingh@...omium.org>, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Florent Revest <revest@...omium.org>
Subject: [PATCH bpf-next v4] libbpf: Expose API to consume one ring at a time

We already provide ring_buffer__epoll_fd to enable use of external
polling systems. However, the only API available to consume the ring
buffer is ring_buffer__consume, which always checks all rings. When
polling for many events, this can be wasteful.

Signed-off-by: Adam Sindelar <adam@...signal.io>
---
v1->v2: Added entry to libbpf.map
v2->v3: Correctly set errno and handle overflow
v3->v4: Fixed an embarrasing typo from zealous autocomplete

 tools/lib/bpf/libbpf.h   |  1 +
 tools/lib/bpf/libbpf.map |  1 +
 tools/lib/bpf/ringbuf.c  | 22 ++++++++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 55b97b2087540..20ccc65eb3f9d 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1195,6 +1195,7 @@ 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_ring(struct ring_buffer *rb, uint32_t ring_id);
 LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb);
 
 struct user_ring_buffer_opts {
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 9c7538dd5835e..42dc418b4672f 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -398,4 +398,5 @@ LIBBPF_1.3.0 {
 		bpf_prog_detach_opts;
 		bpf_program__attach_netfilter;
 		bpf_program__attach_tcx;
+		ring_buffer__consume_ring;
 } LIBBPF_1.2.0;
diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index 02199364db136..457469fc7d71e 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -290,6 +290,28 @@ int ring_buffer__consume(struct ring_buffer *rb)
 	return res;
 }
 
+/* Consume available data from a single RINGBUF map identified by its ID.
+ * The ring ID is returned in epoll_data by epoll_wait when called with
+ * ring_buffer__epoll_fd.
+ */
+int ring_buffer__consume_ring(struct ring_buffer *rb, uint32_t ring_id)
+{
+	struct ring *ring;
+	int64_t res;
+
+	if (ring_id >= rb->ring_cnt)
+		return libbpf_err(-EINVAL);
+
+	ring = &rb->rings[ring_id];
+	res = ringbuf_process_ring(ring);
+	if (res < 0)
+		return libbpf_err(res);
+
+	if (res > INT_MAX)
+		return INT_MAX;
+	return res;
+}
+
 /* Poll for available data and consume records, if any are available.
  * Returns number of records consumed (or INT_MAX, whichever is less), or
  * negative number, if any of the registered callbacks returned error.
-- 
2.39.2