netdev - Re: [PATCH bpf-next RFC v1 3/8] libbpf: Support kernel module function calls

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Date:   Wed, 1 Sep 2021 07:57:01 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...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>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next RFC v1 3/8] libbpf: Support kernel module
 function calls

On Wed, Sep 01, 2021 at 06:25:14AM IST, Andrii Nakryiko wrote:
> On Mon, Aug 30, 2021 at 10:34 AM Kumar Kartikeya Dwivedi
> <memxor@...il.com> wrote:
> >
>
> -ENOCOMMITMESSAGE?
>
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> > ---
> >  tools/lib/bpf/bpf.c             |  3 ++
> >  tools/lib/bpf/libbpf.c          | 71 +++++++++++++++++++++++++++++++--
> >  tools/lib/bpf/libbpf_internal.h |  2 +
> >  3 files changed, 73 insertions(+), 3 deletions(-)
> >
>
> [...]
>
> > @@ -515,6 +521,13 @@ struct bpf_object {
> >         void *priv;
> >         bpf_object_clear_priv_t clear_priv;
> >
> > +       struct {
> > +               struct hashmap *map;
> > +               int *fds;
> > +               size_t cap_cnt;
> > +               __u32 n_fds;
> > +       } kfunc_btf_fds;
> > +
> >         char path[];
> >  };
> >  #define obj_elf_valid(o)       ((o)->efile.elf)
> > @@ -5327,6 +5340,7 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
> >                         ext = &obj->externs[relo->sym_off];
> >                         insn[0].src_reg = BPF_PSEUDO_KFUNC_CALL;
> >                         insn[0].imm = ext->ksym.kernel_btf_id;
> > +                       insn[0].off = ext->ksym.offset;
>
> Just a few lines above we use insn[1].imm =
> ext->ksym.kernel_btf_obj_fd; for EXT_KSYM (for variables). Why are you
> inventing a new form if we already have a pretty consistent pattern?
>

That makes sense. This is all new to me, so I went with what was described in
e6ac2450d6de (bpf: Support bpf program calling kernel function), but I'll rework
it to encode the btf fd like that in the next spin. It also makes the everything
far simpler.

> >                         break;
> >                 case RELO_SUBPROG_ADDR:
> >                         if (insn[0].src_reg != BPF_PSEUDO_FUNC) {
>
> [...]

--
Kartikeya