netdev - Re: [PATCH bpf-next v7 07/11] libbpf: implement bpf_prog_query

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Date:   Mon, 23 May 2022 19:15:10 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH bpf-next v7 07/11] libbpf: implement bpf_prog_query_opts

On Mon, May 23, 2022 at 4:22 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Wed, May 18, 2022 at 3:55 PM Stanislav Fomichev <sdf@...gle.com> wrote:
> >
> > Implement bpf_prog_query_opts as a more expendable version of
> > bpf_prog_query. Expose new prog_attach_flags and attach_btf_func_id as
> > well:
> >
> > * prog_attach_flags is a per-program attach_type; relevant only for
> >   lsm cgroup program which might have different attach_flags
> >   per attach_btf_id
> > * attach_btf_func_id is a new field expose for prog_query which
> >   specifies real btf function id for lsm cgroup attachments
> >
>
> just thoughts aloud... Shouldn't bpf_prog_query() also return link_id
> if the attachment was done with LINK_CREATE? And then attach flags
> could actually be fetched through corresponding struct bpf_link_info.
> That is, bpf_prog_query() returns a list of link_ids, and whatever
> link-specific information can be fetched by querying individual links.
> Seems more logical (and useful overall) to extend struct bpf_link_info
> (you can get it more generically from bpftool, by querying fdinfo,
> etc).

Note that I haven't removed non-link-based APIs because they are easy
to support. That might be an argument in favor of dropping them.
Regarding the implementation: I'm not sure there is an easy way, in
the kernel, to find all links associated with a given bpf_prog?

> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > ---
> >  tools/include/uapi/linux/bpf.h |  5 ++++
> >  tools/lib/bpf/bpf.c            | 42 +++++++++++++++++++++++++++-------
> >  tools/lib/bpf/bpf.h            | 15 ++++++++++++
> >  tools/lib/bpf/libbpf.map       |  1 +
> >  4 files changed, 55 insertions(+), 8 deletions(-)
> >
>
> [...]
>
> >         ret = sys_bpf(BPF_PROG_QUERY, &attr, sizeof(attr));
> >
> > -       if (attach_flags)
> > -               *attach_flags = attr.query.attach_flags;
> > -       *prog_cnt = attr.query.prog_cnt;
> > +       if (OPTS_HAS(opts, prog_cnt))
> > +               opts->prog_cnt = attr.query.prog_cnt;
>
> just use OPTS_SET() instead of OPTS_HAS check

Ah, definitely, for some reason I thought that these are "output"
arguments and OPT_SET won't work for them.

> > +       if (OPTS_HAS(opts, attach_flags))
> > +               opts->attach_flags = attr.query.attach_flags;
> >
> >         return libbpf_err_errno(ret);
> >  }
> >
>
> [...]
>
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 6b36f46ab5d8..24f7a5147bf2 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -452,6 +452,7 @@ LIBBPF_0.8.0 {
> >                 bpf_map_delete_elem_flags;
> >                 bpf_object__destroy_subskeleton;
> >                 bpf_object__open_subskeleton;
> > +               bpf_prog_query_opts;
>
> please put it into LIBBPF_1.0.0 section, 0.8 is closed now

Definitely, will pull new changes and put them into proper place.

Thank you for your review!