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 <tam...@kernel.org>

Reviewed-by: Emil Tsalapatis <e...@etsalapatis.com>

> ---
>  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);