Re: [PATCH bpf 1/6] libbpf: ringbuf: Honor zero consume bounds

[Emil Tsalapatis]

On Sat Jun 13, 2026 at 9:48 PM EDT, Tamir Duberstein wrote:
> ringbuf_process_ring() checks the record bound only after advancing the
> consumer position and invoking the callback. A zero bound therefore
> consumes the first available record.
>
> Return before reading the ring positions when the bound is zero so
> ring_buffer__consume_n() and ring__consume_n() leave all records queued.
>
> Fixes: 4d22ea94ea33 ("libbpf: Add ring__consume_n / ring_buffer__consume_n")
> Assisted-by: Codex:gpt-5.5
> Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxxx>

Reviewed-by: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>

> ---
>  tools/lib/bpf/ringbuf.c                          |  3 +++
>  tools/testing/selftests/bpf/prog_tests/ringbuf.c | 13 +++++++++++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
> index 00ec4837a06d..f2bb619d5a75 100644
> --- a/tools/lib/bpf/ringbuf.c
> +++ b/tools/lib/bpf/ringbuf.c
> @@ -240,6 +240,9 @@ static int64_t ringbuf_process_ring(struct ring *r, size_t n)
>  	bool got_new_data;
>  	void *sample;
>  
> +	if (n == 0)
> +		return 0;
> +
>  	cons_pos = smp_load_acquire(r->consumer_pos);
>  	do {
>  		got_new_data = false;
> diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> index 64520684d2cb..4f0558f14847 100644
> --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> @@ -404,6 +404,7 @@ static int process_n_sample(void *ctx, void *data, size_t len)
>  static void ringbuf_n_subtest(void)
>  {
>  	struct test_ringbuf_n_lskel *skel_n;
> +	struct ring *ring;
>  	int err, i;
>  
>  	skel_n = test_ringbuf_n_lskel__open();
> @@ -431,6 +432,18 @@ static void ringbuf_n_subtest(void)
>  	for (i = 0; i < N_TOT_SAMPLES; i++)
>  		syscall(__NR_getpgid);
>  
> +	ring = ring_buffer__ring(ringbuf, 0);
> +	if (!ASSERT_OK_PTR(ring, "ring_buffer__ring"))
> +		goto cleanup_ringbuf;
> +
> +	err = ring_buffer__consume_n(ringbuf, 0);
> +	if (!ASSERT_EQ(err, 0, "ringbuf_consume_zero"))
> +		goto cleanup_ringbuf;
> +
> +	err = ring__consume_n(ring, 0);
> +	if (!ASSERT_EQ(err, 0, "ring_consume_zero"))
> +		goto cleanup_ringbuf;
> +
>  	/* Consume all samples from the ring buffer in batches of N_SAMPLES */
>  	for (i = 0; i < N_TOT_SAMPLES; i += err) {
>  		err = ring_buffer__consume_n(ringbuf, N_SAMPLES);