Re: [PATCH v3] selftests/bpf: Add ring_buffer__consume_n test.

[Andrii Nakryiko]

On Thu, Apr 25, 2024 at 7:06 AM Andrea Righi <andrea.righi@xxxxxxxxxxxxx> wrote:
>
> Add a testcase for the ring_buffer__consume_n() API.
>
> The test produces multiple samples in a ring buffer, using a
> sys_getpid() fentry prog, and consumes them from user-space in batches,
> rather than consuming all of them greedily, like ring_buffer__consume()
> does.
>
> Link: https://lore.kernel.org/lkml/CAEf4BzaR4zqUpDmj44KNLdpJ=Tpa97GrvzuzVNO5nM6b7oWd1w@xxxxxxxxxxxxxx
> Signed-off-by: Andrea Righi <andrea.righi@xxxxxxxxxxxxx>
> ---
>  tools/testing/selftests/bpf/Makefile          |  2 +-
>  .../selftests/bpf/prog_tests/ringbuf.c        | 64 +++++++++++++++++++
>  .../selftests/bpf/progs/test_ringbuf_n.c      | 47 ++++++++++++++
>  3 files changed, 112 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/test_ringbuf_n.c
>
> ChangeLog v2 -> v3:
>  - move skel_n inside ringbuf_n_subtest()
>
> ChangeLog v1 -> v2:
>  - replace CHECK() with ASSERT_EQ()
>  - fix skel -> skel_n
>  - drop unused "seq" field from struct sample
>

[...]

> +       /* Produce N_TOT_SAMPLES samples in the ring buffer by calling getpid() */
> +       skel_n->bss->value = SAMPLE_VALUE;
> +       for (i = 0; i < N_TOT_SAMPLES; i++)
> +               syscall(__NR_getpgid);
> +
> +       /* 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);
> +               ASSERT_EQ(err, N_SAMPLES, "rb_consume");

if something goes wrong and err is < 0, we might end up with a very
long loop. I changed this to:

if (!ASSERT_EQ(...))
    goto cleanup_ringbuf;

to avoid this problem

> +       }
> +
> +cleanup_ringbuf:
> +       ring_buffer__free(ringbuf);
> +cleanup:
> +       test_ringbuf_n_lskel__destroy(skel_n);
> +}
> +

[...]