netdev - Re: [PATCH bpf-next 5/5] selftests/bpf: add test cases for bpf

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Date:   Wed, 8 Dec 2021 21:50:45 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 5/5] selftests/bpf: add test cases for
 bpf_strncmp()

Hi,
On 12/7/2021 11:09 AM, Andrii Nakryiko wrote:
>> +static struct strncmp_test *strncmp_test_open_and_disable_autoload(void)
>> +{
>> +       struct strncmp_test *skel;
>> +       struct bpf_program *prog;
>> +
>> +       skel = strncmp_test__open();
>> +       if (libbpf_get_error(skel))
>> +               return skel;
>> +
>> +       bpf_object__for_each_program(prog, skel->obj)
>> +               bpf_program__set_autoload(prog, false);
> I think this is a wrong "code economy". You save few lines of code,
> but make tests harder to follow. Just do 4 lines of code for each
> subtest:
>
> skel = strncmp_test__open();
> if (!ASSERT_OK_PTR(skel, "skel_open"))
>     return;
>
> bpf_object__for_each_program(prog, skel->obj)
>     bpf_program__set_autoload(prog, false);
>
>
> It makes tests more self-contained and easier to follow. Also if some
> tests need to do something slightly different it's easier to modify
> them, as they are not coupled to some common helper. DRY is good where
> it makes sense, but it also increases code coupling and more "jumping
> around" in code, so it shouldn't be applied blindly.
Thanks for your suggestion on DRY topic. Will do in v2.
> +
> +static int trigger_strncmp(const struct strncmp_test *skel)
> +{
> +       struct timespec wait = {.tv_sec = 0, .tv_nsec = 1};
> +
> +       nanosleep(&wait, NULL);
> all the other tests are just doing usleep(1), why using this more verbose way?
Will do in v2.
>> +
>> +static __always_inline bool called_by_target_pid(void)
>> +{
>> +       __u32 pid = bpf_get_current_pid_tgid() >> 32;
>> +
>> +       return pid == target_pid;
>> +}
> again, what's the point of this helper? it's used once and you'd
> actually save the code by doing the following inline:
>
> if ((bpf_get_current_pid_tgid() >> 32) != target_pid)
>     return 0;
Will do in v2.
>> +
>> +SEC("tp/syscalls/sys_enter_nanosleep")
>> +int do_strncmp(void *ctx)
>> +{
>> +       if (!called_by_target_pid())
>> +               return 0;
>> +
>> +       cmp_ret = bpf_strncmp(str, STRNCMP_STR_SZ, target);
>> +
>> +       return 0;
>> +}
>> +
>> +SEC("tp/syscalls/sys_enter_nanosleep")
>> +int strncmp_bad_not_const_str_size(void *ctx)
>> +{
> probably worth leaving a short comment explaining that this program
> should fail because ...
OK. Will do in v2.

Regards,
Tao