Date:   Fri, 30 Oct 2020 08:50:37 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin Lau <kafai@...com>,
        john fastabend <john.fastabend@...il.com>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Lawrence Brakmo <brakmo@...com>, alexanderduyck@...com
Subject: Re: [bpf-next PATCH 4/4] selftests/bpf: Migrate tcpbpf_user.c to use
 BPF skeleton

On Thu, Oct 29, 2020 at 7:30 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Oct 29, 2020 at 5:42 PM Alexander Duyck
> <alexander.duyck@...il.com> wrote:
> >
> > On Thu, Oct 29, 2020 at 4:20 PM Andrii Nakryiko
> > <andrii.nakryiko@...il.com> wrote:
> > >
> > > On Thu, Oct 29, 2020 at 12:57 AM Alexander Duyck
> > > <alexander.duyck@...il.com> wrote:
> > > >
> > > > From: Alexander Duyck <alexanderduyck@...com>
> > > >
> > > > Update tcpbpf_user.c to make use of the BPF skeleton. Doing this we can
> > > > simplify test_tcpbpf_user and reduce the overhead involved in setting up
> > > > the test.
> > > >
> > > > Signed-off-by: Alexander Duyck <alexanderduyck@...com>
> > > > ---
> > >
> > > Few suggestions below, but overall looks good:
> > >
> > > Acked-by: Andrii Nakryiko <andrii@...nel.org>
> > >
> > > >  .../testing/selftests/bpf/prog_tests/tcpbpf_user.c |   48 +++++++++-----------
> > > >  1 file changed, 21 insertions(+), 27 deletions(-)
> > > >
> > > > diff --git a/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c b/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c
> > > > index 4e1190894e1e..7e92c37976ac 100644
> > > > --- a/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c
> > > > +++ b/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c
> > > > @@ -5,6 +5,7 @@
> > > >
> > > >  #include "test_tcpbpf.h"
> > > >  #include "cgroup_helpers.h"
> > > > +#include "test_tcpbpf_kern.skel.h"
> > > >
> > > >  #define LO_ADDR6 "::1"
> > > >  #define CG_NAME "/tcpbpf-user-test"
> > > > @@ -162,39 +163,32 @@ static void run_test(int map_fd, int sock_map_fd)
> > > >
> > > >  void test_tcpbpf_user(void)
> > > >  {
> > > > -       const char *file = "test_tcpbpf_kern.o";
> > > > -       int prog_fd, map_fd, sock_map_fd;
> > > > -       struct bpf_object *obj;
> > > > +       struct test_tcpbpf_kern *skel;
> > > > +       int map_fd, sock_map_fd;
> > > > +       struct bpf_link *link;
> > > >         int cg_fd = -1;
> > > > -       int rv;
> > > > -
> > > > -       cg_fd = cgroup_setup_and_join(CG_NAME);
> > > > -       if (CHECK_FAIL(cg_fd < 0))
> > > > -               goto err;
> > > >
> > > > -       if (CHECK_FAIL(bpf_prog_load(file, BPF_PROG_TYPE_SOCK_OPS, &obj, &prog_fd))) {
> > > > -               fprintf(stderr, "FAILED: load_bpf_file failed for: %s\n", file);
> > > > -               goto err;
> > > > -       }
> > > > +       skel = test_tcpbpf_kern__open_and_load();
> > > > +       if (CHECK(!skel, "open and load skel", "failed"))
> > > > +               return;
> > > >
> > > > -       rv = bpf_prog_attach(prog_fd, cg_fd, BPF_CGROUP_SOCK_OPS, 0);
> > > > -       if (CHECK_FAIL(rv)) {
> > > > -               fprintf(stderr, "FAILED: bpf_prog_attach: %d (%s)\n",
> > > > -                      errno, strerror(errno));
> > > > -               goto err;
> > > > -       }
> > > > +       cg_fd = test__join_cgroup(CG_NAME);
> > > > +       if (CHECK_FAIL(cg_fd < 0))
> > >
> > > please use either CHECK() or one of the newer ASSERT_xxx() macro (also
> > > defined in test_progs.h), CHECK_FAIL should be avoided in general.
> >
> > So the plan I had was to actually move over to the following:
> >         cg_fd = test__join_cgroup(CG_NAME);
> >         if (CHECK_FAIL(cg_fd < 0))
> >                 goto cleanup_skel;
> >
> > It still makes use of CHECK_FAIL but it looks like test__join_cgroup
> > already takes care of error messaging so using CHECK_FAIL in this case
> > makes more sense.
>
> CHECK (and ASSERT) leave a paper-trail in verbose test log, so it
> makes it easier to debug tests, if something fails. CHECK_FAIL is
> invisible, unless if fails. So CHECK_FAIL should be used only for
> things that are happening on the order of hundreds of instances per
> test, or more.

Okay, well in that case I will go through and replace the CHECK_FAIL
calls with a CHECK.

> >
> > > > +               goto cleanup_skel;
> > > >
> > > > -       map_fd = bpf_find_map(__func__, obj, "global_map");
> > > > -       if (CHECK_FAIL(map_fd < 0))
> > > > -               goto err;
> > > > +       map_fd = bpf_map__fd(skel->maps.global_map);
> > > > +       sock_map_fd = bpf_map__fd(skel->maps.sockopt_results);
> > > >
> > > > -       sock_map_fd = bpf_find_map(__func__, obj, "sockopt_results");
> > > > -       if (CHECK_FAIL(sock_map_fd < 0))
> > > > -               goto err;
> > > > +       link = bpf_program__attach_cgroup(skel->progs.bpf_testcb, cg_fd);
> > >
> > > you can do skel->links.bpf_testcb = bpf_program__attach_cgroup() and
> > > skeleton's __destroy() call will take care of destroying the link
> >
> > Okay, I can look into using that. Actually this has me wondering if
> > there wouldn't be some way to make use of test_tcpbpf_kern__attach to
> > achieve this in some standard way. I'll get that sorted before I
> > submit v2.
>
> cgroup BPF programs can't be auto-attached, because they expect cgroup
> FD, which you can't provide at compilation time (declaratively) in BPF
> code. So it has to be manually attached. skeleton's attach() will just
> ignore such programs.

Yeah, I figured that out after reviewing the code further.

Thanks.

- Alex

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