netdev - Re: [PATCH bpf-next v3 13/15] tools/bpf: selftests: implement sample tcp/tcp6 bpf

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Date:   Mon, 22 Jun 2020 23:56:10 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...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>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v3 13/15] tools/bpf: selftests: implement sample
 tcp/tcp6 bpf_iter programs

On Mon, Jun 22, 2020 at 5:38 PM Yonghong Song <yhs@...com> wrote:
>
> In my VM, I got identical result compared to /proc/net/{tcp,tcp6}.
> For tcp6:
>   $ cat /proc/net/tcp6
>     sl  local_address                         remote_address                        st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
>      0: 00000000000000000000000000000000:0016 00000000000000000000000000000000:0000 0A 00000000:00000000 00:00000001 00000000     0        0 17955 1 000000003eb3102e 100 0 0 10 0
>
>   $ cat /sys/fs/bpf/p1
>     sl  local_address                         remote_address                        st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
>      0: 00000000000000000000000000000000:0016 00000000000000000000000000000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 17955 1 000000003eb3102e 100 0 0 10 0
>
> For tcp:
>   $ cat /proc/net/tcp
>   sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
>    0: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 2666 1 000000007152e43f 100 0 0 10 0
>   $ cat /sys/fs/bpf/p2
>   sl  local_address                         remote_address                        st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
>    1: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 2666 1 000000007152e43f 100 0 0 10 0
>
> Signed-off-by: Yonghong Song <yhs@...com>
> ---

Looks reasonable, to the extent possible ;)

Acked-by: Andrii Nakryiko <andriin@...com>

>  tools/testing/selftests/bpf/progs/bpf_iter.h  |  15 ++
>  .../selftests/bpf/progs/bpf_iter_tcp4.c       | 235 ++++++++++++++++
>  .../selftests/bpf/progs/bpf_iter_tcp6.c       | 250 ++++++++++++++++++
>  3 files changed, 500 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_tcp4.c
>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_tcp6.c
>

[...]

> +static int hlist_unhashed_lockless(const struct hlist_node *h)
> +{
> +        return !(h->pprev);
> +}
> +
> +static int timer_pending(const struct timer_list * timer)
> +{
> +       return !hlist_unhashed_lockless(&timer->entry);
> +}
> +
> +extern unsigned CONFIG_HZ __kconfig __weak;

Why the __weak? We expect to have /proc/kconfig.gz in other tests
anyway? __weak will make CONFIG_HZ to be a zero and you'll get a bunch
of divisions by zero.

> +
> +#define USER_HZ                100
> +#define NSEC_PER_SEC   1000000000ULL
> +static clock_t jiffies_to_clock_t(unsigned long x)
> +{
> +       /* The implementation here tailored to a particular
> +        * setting of USER_HZ.
> +        */
> +       u64 tick_nsec = (NSEC_PER_SEC + CONFIG_HZ/2) / CONFIG_HZ;
> +       u64 user_hz_nsec = NSEC_PER_SEC / USER_HZ;
> +
> +       if ((tick_nsec % user_hz_nsec) == 0) {
> +               if (CONFIG_HZ < USER_HZ)
> +                       return x * (USER_HZ / CONFIG_HZ);
> +               else
> +                       return x / (CONFIG_HZ / USER_HZ);
> +       }
> +       return x * tick_nsec/user_hz_nsec;
> +}
> +

[...]

> +       if (sk_common->skc_family != AF_INET)
> +               return 0;
> +
> +       tp = bpf_skc_to_tcp_sock(sk_common);
> +       if (tp) {
> +               return dump_tcp_sock(seq, tp, uid, seq_num);
> +       }

nit: unnecessary {}

> +
> +       tw = bpf_skc_to_tcp_timewait_sock(sk_common);
> +       if (tw)
> +               return dump_tw_sock(seq, tw, uid, seq_num);
> +
> +       req = bpf_skc_to_tcp_request_sock(sk_common);
> +       if (req)
> +               return dump_req_sock(seq, req, uid, seq_num);
> +
> +       return 0;
> +}

[...]

> +static int timer_pending(const struct timer_list * timer)
> +{
> +       return !hlist_unhashed_lockless(&timer->entry);
> +}
> +
> +extern unsigned CONFIG_HZ __kconfig __weak;

same about __weak here

> +
> +#define USER_HZ                100
> +#define NSEC_PER_SEC   1000000000ULL
> +static clock_t jiffies_to_clock_t(unsigned long x)
> +{
> +       /* The implementation here tailored to a particular
> +        * setting of USER_HZ.
> +        */
> +       u64 tick_nsec = (NSEC_PER_SEC + CONFIG_HZ/2) / CONFIG_HZ;
> +       u64 user_hz_nsec = NSEC_PER_SEC / USER_HZ;
> +
> +       if ((tick_nsec % user_hz_nsec) == 0) {
> +               if (CONFIG_HZ < USER_HZ)
> +                       return x * (USER_HZ / CONFIG_HZ);
> +               else
> +                       return x / (CONFIG_HZ / USER_HZ);
> +       }
> +       return x * tick_nsec/user_hz_nsec;
> +}

nit: jiffies_to_clock_t() implementation looks like an overkill for
this use case... Would it be just `x / CONFIG_HZ * NSEC_PER_SEC` with
some potential rounding error?

> +
> +static clock_t jiffies_delta_to_clock_t(long delta)
> +{
> +       if (delta <= 0)
> +               return 0;
> +
> +       return jiffies_to_clock_t(delta);
> +}
> +

[...]