netdev - Re: [PATCH v2 bpf-next 2/3] libbpf: introduce bpf_prog_test_run_xattr

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Message-ID: <CAEf4BzYDsBMmBBtgauqdR9HYDeRG-GbMMTG6FUDbpWgOuU_Ljg@mail.gmail.com>
Date:   Wed, 23 Sep 2020 18:11:12 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH v2 bpf-next 2/3] libbpf: introduce bpf_prog_test_run_xattr_opts

On Wed, Sep 23, 2020 at 4:54 PM Song Liu <songliubraving@...com> wrote:
>
>
>
> > On Sep 23, 2020, at 12:31 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> >
> > On Wed, Sep 23, 2020 at 9:55 AM Song Liu <songliubraving@...com> wrote:
> >>
> >> This API supports new field cpu_plus in bpf_attr.test.
> >>
> >> Acked-by: John Fastabend <john.fastabend@...il.com>
> >> Signed-off-by: Song Liu <songliubraving@...com>
> >> ---
> >> tools/lib/bpf/bpf.c      | 13 ++++++++++++-
> >> tools/lib/bpf/bpf.h      | 11 +++++++++++
> >> tools/lib/bpf/libbpf.map |  1 +
> >> 3 files changed, 24 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> >> index 2baa1308737c8..3228dd60fa32f 100644
> >> --- a/tools/lib/bpf/bpf.c
> >> +++ b/tools/lib/bpf/bpf.c
> >> @@ -684,7 +684,8 @@ int bpf_prog_test_run(int prog_fd, int repeat, void *data, __u32 size,
> >>        return ret;
> >> }
> >>
> >> -int bpf_prog_test_run_xattr(struct bpf_prog_test_run_attr *test_attr)
> >> +int bpf_prog_test_run_xattr_opts(struct bpf_prog_test_run_attr *test_attr,
> >> +                                const struct bpf_prog_test_run_opts *opts)
> >
> > opts are replacement for test_attr, not an addition to it. We chose to
> > use _xattr suffix for low-level APIs previously, but it's already
> > "taken". So I'd suggest to go with just  bpf_prog_test_run_ops and
> > have prog_fd as a first argument and then put all the rest of
> > test_run_attr into opts.
>
> One question on this: from the code, most (if not all) of these xxx_opts
> are used as input only. For example:
>
> LIBBPF_API int bpf_prog_bind_map(int prog_fd, int map_fd,
>                                  const struct bpf_prog_bind_opts *opts);
>
> However, bpf_prog_test_run_attr contains both input and output. Do you
> have any concern we use bpf_prog_test_run_opts for both input and output?
>

I think it should be ok. opts are about passing optional things in a
way that would be backward/forward compatible. Whether it's input
only, output only, or input/output is secondary. We haven't had a need
for output params yet, so this will be the first, but I think it fits
here just fine. Just document it in the struct definition clearly and
that's it. As for the mechanics, we might want to do OPTS_SET() macro,
that will set some fields only if the user provided enough memory to
fir that output parameter. That should work here pretty cleanly,
right?

> Thanks,
> Song
>
>
> > BTW, it's also probably overdue to have a higher-level
> > bpf_program__test_run(), which can re-use the same
> > bpf_prog_test_run_opts options struct. It would be more convenient to
> > use it with libbpf bpf_object/bpf_program APIs.
> >
> >> {
> >>        union bpf_attr attr;
> >>        int ret;
> >> @@ -693,6 +694,11 @@ int bpf_prog_test_run_xattr(struct bpf_prog_test_run_attr *test_attr)
> >>                return -EINVAL;
> >>
> >>        memset(&attr, 0, sizeof(attr));
> >> +       if (opts) {
> >
> > you don't need to check opts for being not NULL, OPTS_VALID handle that already.
> >
> >> +               if (!OPTS_VALID(opts, bpf_prog_test_run_opts))
> >> +                       return -EINVAL;
> >> +               attr.test.cpu_plus = opts->cpu_plus;
> >
> > And here you should use OPTS_GET(), please see other examples in
> > libbpf for proper usage.
> >
> >
> >> +       }
> >>        attr.test.prog_fd = test_attr->prog_fd;
> >>        attr.test.data_in = ptr_to_u64(test_attr->data_in);
> >>        attr.test.data_out = ptr_to_u64(test_attr->data_out);
> >> @@ -712,6 +718,11 @@ int bpf_prog_test_run_xattr(struct bpf_prog_test_run_attr *test_attr)
> >>        return ret;
> >> }
> >>
> >
> > [...]
>