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

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Date:   Thu, 30 Apr 2020 05:12:23 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.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 Apr 29, 2020, at 7:23 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> 
> 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?

Not really, will remove it. 

> 
>> +#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;

Why would compile remove it? Is it because "static" or "no initialized?
Would "__u64 count;" work?

For "__u64 count = 0;", checkpatch.pl generates an error:

ERROR: do not initialise globals to 0
#92: FILE: tools/testing/selftests/bpf/progs/test_enable_stats.c:11:
+__u64 count = 0;

Thanks,
Song