[PATCH bpf 1/2] libbpf: fix ring_buffer__poll() to return number of consumed samples

[PATCH bpf 1/2] libbpf: fix ring_buffer__poll() to return number of consumed samples

[Andrii Nakryiko]

Fix ring_buffer__poll() to return the number of non-discarded records
consumed, just like its documentation states. It's also consistent with
ring_buffer__consume() return. Fix up selftests with wrong expected results.

Fixes: bf99c936f947 ("libbpf: Add BPF ring buffer support")
Fixes: cb1c9ddd5525 ("selftests/bpf: Add BPF ringbuf selftests")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/ringbuf.c                                | 2 +-
 tools/testing/selftests/bpf/prog_tests/ringbuf.c       | 2 +-
 tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index 5c6522c89af1..98537ff2679e 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -278,7 +278,7 @@ int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
 		err = ringbuf_process_ring(ring);
 		if (err < 0)
 			return err;
-		res += cnt;
+		res += err;
 	}
 	return cnt < 0 ? -errno : res;
 }
diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
index c1650548433c..1a48c6f7f54e 100644
--- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
+++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
@@ -217,7 +217,7 @@ void test_ringbuf(void)
 	if (CHECK(err, "join_bg", "err %d\n", err))
 		goto cleanup;
 
-	if (CHECK(bg_ret != 1, "bg_ret", "epoll_wait result: %ld", bg_ret))
+	if (CHECK(bg_ret <= 0, "bg_ret", "epoll_wait result: %ld", bg_ret))
 		goto cleanup;
 
 	/* 3 rounds, 2 samples each */
diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c b/tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c
index 78e450609803..d37161e59bb2 100644
--- a/tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c
+++ b/tools/testing/selftests/bpf/prog_tests/ringbuf_multi.c
@@ -81,7 +81,7 @@ void test_ringbuf_multi(void)
 
 	/* poll for samples, should get 2 ringbufs back */
 	err = ring_buffer__poll(ringbuf, -1);
-	if (CHECK(err != 4, "poll_res", "expected 4 records, got %d\n", err))
+	if (CHECK(err != 2, "poll_res", "expected 2 records, got %d\n", err))
 		goto cleanup;
 
 	/* expect extra polling to return nothing */
-- 
2.24.1

[PATCH bpf 2/2] selftests/bpf: drain ringbuf samples at the end of test

[Andrii Nakryiko]

Avoid occasional test failures due to the last sample being delayed to
another ring_buffer__poll() call. Instead, drain samples completely with
ring_buffer__consume(). This is supposed to fix a rare and non-deterministic
test failure in libbpf CI.

Fixes: cb1c9ddd5525 ("selftests/bpf: Add BPF ringbuf selftests")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/prog_tests/ringbuf.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
index 1a48c6f7f54e..fddbc5db5d6a 100644
--- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
+++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
@@ -220,6 +220,12 @@ void test_ringbuf(void)
 	if (CHECK(bg_ret <= 0, "bg_ret", "epoll_wait result: %ld", bg_ret))
 		goto cleanup;
 
+	/* due to timing variations, there could still be non-notified
+	 * samples, so consume them here to collect all the samples
+	 */
+	err = ring_buffer__consume(ringbuf);
+	CHECK(err < 0, "rb_consume", "failed: %d\b", err);
+
 	/* 3 rounds, 2 samples each */
 	cnt = atomic_xchg(&sample_cnt, 0);
 	CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt);
-- 
2.24.1

Re: [PATCH bpf 1/2] libbpf: fix ring_buffer__poll() to return number of consumed samples

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf.git (refs/heads/master):

On Mon, 30 Nov 2020 14:33:35 -0800 you wrote:
> Fix ring_buffer__poll() to return the number of non-discarded records
> consumed, just like its documentation states. It's also consistent with
> ring_buffer__consume() return. Fix up selftests with wrong expected results.
> 
> Fixes: bf99c936f947 ("libbpf: Add BPF ring buffer support")
> Fixes: cb1c9ddd5525 ("selftests/bpf: Add BPF ringbuf selftests")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> 
> [...]

Here is the summary with links:
  - [bpf,1/2] libbpf: fix ring_buffer__poll() to return number of consumed samples
    https://git.kernel.org/bpf/bpf/c/f6a8250ea1e4
  - [bpf,2/2] selftests/bpf: drain ringbuf samples at the end of test
    https://git.kernel.org/bpf/bpf/c/156c9b70dbfb

You are awesome, thank you!
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