linux-kernel - Re: [PATCH bpf-next v3] libbpf: Fix expected_attach

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Message-ID: <CAEf4BzZpdMx7ZV6V6pJKLkq3BtdRrqj8Vo09YVSN5YApNtCa3Q@mail.gmail.com>
Date: Thu, 19 Sep 2024 06:20:57 +0200
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Tao Chen <chen.dylane@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v3] libbpf: Fix expected_attach_type set when
 kernel not support

On Thu, Sep 19, 2024 at 4:05 AM Tao Chen <chen.dylane@...il.com> wrote:
>
> 在 2024/9/14 23:40, Tao Chen 写道:
> > The commit "5902da6d8a52" set expected_attach_type again with
> > field of bpf_program after libpf_prepare_prog_load, which makes
> > expected_attach_type = 0 no sense when kenrel not support the
> > attach_type feature, so fix it.
> >
> > Fixes: 5902da6d8a52 ("libbpf: Add uprobe multi link support to bpf_program__attach_usdt")
> > Suggested-by: Jiri Olsa <jolsa@...nel.org>
> > Signed-off-by: Tao Chen <chen.dylane@...il.com>
> > ---
> >   tools/lib/bpf/libbpf.c | 12 ++++++++----
> >   1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > Change list:
> > - v2 -> v3:
> >      - update BPF_TRACE_UPROBE_MULTI both in prog and opts suggedted by
> >        Andrri
> > - v1 -> v2:
> >      - restore the original initialization way suggested by Jiri
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 219facd0e66e..a78e24ff354b 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -7352,8 +7352,14 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
> >               opts->prog_flags |= BPF_F_XDP_HAS_FRAGS;
> >
> >       /* special check for usdt to use uprobe_multi link */
> > -     if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK))
> > +     if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK)) {
> > +             /* for BPF_TRACE_KPROBE_MULTI, user might want to query exected_attach_type
> > +              * in prog, and expected_attach_type we set in kenrel is from opts, so we
> > +              * update both.
> > +              */
> >               prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
> > +             opts->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
> > +     }
> >
> >       if ((def & SEC_ATTACH_BTF) && !prog->attach_btf_id) {
> >               int btf_obj_fd = 0, btf_type_id = 0, err;
> > @@ -7443,6 +7449,7 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
> >       load_attr.attach_btf_id = prog->attach_btf_id;
> >       load_attr.kern_version = kern_version;
> >       load_attr.prog_ifindex = prog->prog_ifindex;
> > +     load_attr.expected_attach_type = prog->expected_attach_type;
> >
> >       /* specify func_info/line_info only if kernel supports them */
> >       if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
> > @@ -7474,9 +7481,6 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
> >               insns_cnt = prog->insns_cnt;
> >       }
> >
> > -     /* allow prog_prepare_load_fn to change expected_attach_type */
> > -     load_attr.expected_attach_type = prog->expected_attach_type;
> > -
> >       if (obj->gen_loader) {
> >               bpf_gen__prog_load(obj->gen_loader, prog->type, prog->name,
> >                                  license, insns, insns_cnt, &load_attr,
>
> Hi, guys, please review this patch again, the previous versions:

It looks good, but bpf-next is closed right now due to merge window.
I'll apply when the tree is open again.

> v1:
> https://lore.kernel.org/bpf/20240913121627.153898-1-chen.dylane@gmail.com/
> v2:
> https://lore.kernel.org/bpf/20240913164355.176021-1-chen.dylane@gmail.com/
>
> --
> Best Regards
> Dylane Chen