netdev - Re: [PATCH v8 bpf-next 3/3] bpf: add selftest for BPF_ENABLE

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Date:   Wed, 29 Apr 2020 19:23:12 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v8 bpf-next 3/3] bpf: add selftest for BPF_ENABLE_STATS

On Tue, Apr 28, 2020 at 11:47 PM Song Liu <songliubraving@...com> wrote:
>
> Add test for BPF_ENABLE_STATS, which should enable run_time_ns stats.
>
> ~/selftests/bpf# ./test_progs -t enable_stats  -v
> test_enable_stats:PASS:skel_open_and_load 0 nsec
> test_enable_stats:PASS:get_stats_fd 0 nsec
> test_enable_stats:PASS:attach_raw_tp 0 nsec
> test_enable_stats:PASS:get_prog_info 0 nsec
> test_enable_stats:PASS:check_stats_enabled 0 nsec
> test_enable_stats:PASS:check_run_cnt_valid 0 nsec
> Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  .../selftests/bpf/prog_tests/enable_stats.c   | 46 +++++++++++++++++++
>  .../selftests/bpf/progs/test_enable_stats.c   | 18 ++++++++
>  2 files changed, 64 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/enable_stats.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_enable_stats.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/enable_stats.c b/tools/testing/selftests/bpf/prog_tests/enable_stats.c
> new file mode 100644
> index 000000000000..cb5e34dcfd42
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/enable_stats.c
> @@ -0,0 +1,46 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <test_progs.h>
> +#include <sys/mman.h>

is this header used for anything?

> +#include "test_enable_stats.skel.h"
> +
> +void test_enable_stats(void)
> +{

[...]

> +
> +char _license[] SEC("license") = "GPL";
> +
> +static __u64 count;

this is actually very unreliable, because compiler might decide to
just remove this variable. It should be either `static volatile`, or
better use zero-initialized global variable:

__u64 count = 0;

> +
> +SEC("raw_tracepoint/sys_enter")
> +int test_enable_stats(void *ctx)
> +{
> +       count += 1;
> +       return 0;
> +}
> --
> 2.24.1
>