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References: <20240425140627.112728-1-andrea.righi@canonical.com>
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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date: Thu, 25 Apr 2024 11:47:07 -0700
Message-ID: <CAEf4BzYO=yo15WidtJqe_QaMrj+h7VUyufw7xN2XS0GG8Xh8fQ@mail.gmail.com>
Subject: Re: [PATCH v3] selftests/bpf: Add ring_buffer__consume_n test.
To: Andrea Righi <andrea.righi@canonical.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, Eduard Zingerman <eddyz87@gmail.com>, 
	Mykola Lysenko <mykolal@fb.com>, Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, 
	Martin KaFai Lau <martin.lau@linux.dev>, Song Liu <song@kernel.org>, 
	Yonghong Song <yonghong.song@linux.dev>, John Fastabend <john.fastabend@gmail.com>, 
	KP Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, 
	Jiri Olsa <jolsa@kernel.org>, Shuah Khan <shuah@kernel.org>, linux-kernel@vger.kernel.org, 
	bpf@vger.kernel.org, linux-kselftest@vger.kernel.org
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On Thu, Apr 25, 2024 at 7:06=E2=80=AFAM Andrea Righi <andrea.righi@canonica=
l.com> 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=3DTpa97Grvzu=
zVNO5nM6b7oWd1w@mail.gmail.com
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> ---
>  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 ge=
tpid() */
> +       skel_n->bss->value =3D SAMPLE_VALUE;
> +       for (i =3D 0; i < N_TOT_SAMPLES; i++)
> +               syscall(__NR_getpgid);
> +
> +       /* Consume all samples from the ring buffer in batches of N_SAMPL=
ES */
> +       for (i =3D 0; i < N_TOT_SAMPLES; i +=3D err) {
> +               err =3D 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);
> +}
> +

[...]