netdev - Re: [PATCH bpf-next] bpf: Add BPF-helper for accessing CLOCK

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Date:   Wed, 3 Aug 2022 10:29:53 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     Kurt Kanzenbach <kurt@...utronix.de>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Joanne Koong <joannelkoong@...il.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Geliang Tang <geliang.tang@...e.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: Add BPF-helper for accessing CLOCK_TAI

On Wed, Aug 3, 2022 at 2:29 AM Maciej Fijalkowski
<maciej.fijalkowski@...el.com> wrote:
>
> On Wed, Aug 03, 2022 at 08:29:29AM +0200, Kurt Kanzenbach wrote:
> > On Tue Aug 02 2022, Alexei Starovoitov wrote:
> > > On Tue, Aug 2, 2022 at 12:06 AM Kurt Kanzenbach <kurt@...utronix.de> wrote:
> > >>
> > >> Hi Alexei,
> > >>
> > >> On Tue Jun 07 2022, Alexei Starovoitov wrote:
> > >> > Anyway I guess new helper bpf_ktime_get_tai_ns() is ok, since
> > >> > it's so trivial, but selftest is necessary.
> > >>
> > >> So, I did write a selftest [1] for testing bpf_ktime_get_tai_ns() and
> > >> verifying that the access to the clock works. It uses AF_XDP sockets and
> > >> timestamps the incoming packets. The timestamps are then validated in
> > >> user space.
> > >>
> > >> Since AF_XDP related code is migrating from libbpf to libxdp, I'm
> > >> wondering if that sample fits into the kernel's selftests or not. What
> > >> kind of selftest are you looking for?
> > >
> > > Please use selftests/bpf framework.
> > > There are plenty of networking tests in there.
> > > bpf_ktime_get_tai_ns() doesn't have to rely on af_xdp.
> >
> > OK.
> >
> > > It can be skb based.
>
> FWIW there is xskxceiver and libbpf's xsk part in selftests/bpf framework,
> so your initial work should be fine in there. Personally I found both
> (AF_XDP and SKB one, below) tests valuable.

test_progs is always tested on each patch/patch set. xskxceiver can
potentially break without anyone noticing for a while. So having
something like this in test_progs is much better.

>
> Later on, if we add a support to xskxceiver for loading external BPF progs
> then your sample would just become another test case in there.
>
> >
> > Something like this?
> >
> > +++ b/tools/testing/selftests/bpf/prog_tests/check_tai.c
> > @@ -0,0 +1,57 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (C) 2022 Linutronix GmbH */
> > +
> > +#include <test_progs.h>
> > +#include <network_helpers.h>
> > +
> > +#include <time.h>
> > +#include <stdint.h>
> > +
> > +#define TAI_THRESHOLD        1000000000ULL /* 1s */
> > +#define NSEC_PER_SEC 1000000000ULL
> > +
> > +static __u64 ts_to_ns(const struct timespec *ts)
> > +{
> > +     return ts->tv_sec * NSEC_PER_SEC + ts->tv_nsec;
> > +}
> > +
> > +void test_tai(void)
> > +{
> > +     struct __sk_buff skb = {
> > +             .tstamp = 0,
> > +             .hwtstamp = 0,
> > +     };
> > +     LIBBPF_OPTS(bpf_test_run_opts, topts,
> > +             .data_in = &pkt_v4,
> > +             .data_size_in = sizeof(pkt_v4),
> > +             .ctx_in = &skb,
> > +             .ctx_size_in = sizeof(skb),
> > +             .ctx_out = &skb,
> > +             .ctx_size_out = sizeof(skb),
> > +     );
> > +     struct timespec now_tai;
> > +     struct bpf_object *obj;
> > +     int ret, prog_fd;
> > +
> > +     ret = bpf_prog_test_load("./test_tai.o",
> > +                              BPF_PROG_TYPE_SCHED_CLS, &obj, &prog_fd);
> > +     if (!ASSERT_OK(ret, "load"))
> > +             return;
> > +     ret = bpf_prog_test_run_opts(prog_fd, &topts);
> > +     ASSERT_OK(ret, "test_run");
> > +
> > +     /* TAI != 0 */
> > +     ASSERT_NEQ(skb.tstamp, 0, "tai_ts0_0");
> > +     ASSERT_NEQ(skb.hwtstamp, 0, "tai_ts0_1");
> > +
> > +     /* TAI is moving forward only */
> > +     ASSERT_GT(skb.hwtstamp, skb.tstamp, "tai_forward");
> > +
> > +     /* Check for reasoneable range */
> > +     ret = clock_gettime(CLOCK_TAI, &now_tai);
> > +     ASSERT_EQ(ret, 0, "tai_gettime");
> > +     ASSERT_TRUE((ts_to_ns(&now_tai) - skb.hwtstamp) < TAI_THRESHOLD,
> > +                 "tai_range");
> > +
> > +     bpf_object__close(obj);
> > +}
> > diff --git a/tools/testing/selftests/bpf/progs/test_tai.c b/tools/testing/selftests/bpf/progs/test_tai.c
> > new file mode 100644
> > index 000000000000..34ac4175e29d
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/test_tai.c
> > @@ -0,0 +1,17 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (C) 2022 Linutronix GmbH */
> > +
> > +#include <linux/bpf.h>
> > +#include <bpf/bpf_helpers.h>
> > +
> > +char _license[] SEC("license") = "GPL";
> > +
> > +SEC("tc")
> > +int save_tai(struct __sk_buff *skb)
> > +{
> > +     /* Save TAI timestamps */
> > +     skb->tstamp = bpf_ktime_get_tai_ns();
> > +     skb->hwtstamp = bpf_ktime_get_tai_ns();
> > +
> > +     return 0;
> > +}
>
>