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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andriin@fb.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	Martin KaFai Lau <kafai@fb.com>, David Miller <davem@redhat.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Wenbo Zhang <ethercflow@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Brendan Gregg <bgregg@netflix.com>,
	Florent Revest <revest@chromium.org>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v8 bpf-next 07/13] bpf: Add btf_struct_ids_match function
Date: Wed, 29 Jul 2020 10:51:26 -0700
Message-ID: <CAEf4BzZ26StciUpDas1Mdi1gY_LJChjkUEBvqzuZuhFuAAibLQ@mail.gmail.com> (raw)
In-Reply-To: <20200729160419.GM1319041@krava>

On Wed, Jul 29, 2020 at 9:04 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Tue, Jul 28, 2020 at 04:35:16PM -0700, Andrii Nakryiko wrote:
>
> SNIP
>
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index bae557ff2da8..c981e258fed3 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -1306,6 +1306,8 @@ int btf_struct_access(struct bpf_verifier_log *log,
> > >                       const struct btf_type *t, int off, int size,
> > >                       enum bpf_access_type atype,
> > >                       u32 *next_btf_id);
> > > +bool btf_struct_ids_match(struct bpf_verifier_log *log,
> > > +                         int off, u32 id, u32 mid);
> > >  int btf_resolve_helper_id(struct bpf_verifier_log *log,
> > >                           const struct bpf_func_proto *fn, int);
> > >
> > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > > index 1ab5fd5bf992..562d4453fad3 100644
> > > --- a/kernel/bpf/btf.c
> > > +++ b/kernel/bpf/btf.c
> > > @@ -4140,6 +4140,35 @@ int btf_struct_access(struct bpf_verifier_log *log,
> > >         return -EINVAL;
> > >  }
> > >
> > > +bool btf_struct_ids_match(struct bpf_verifier_log *log,
> > > +                         int off, u32 id, u32 mid)

just realized that if id == mid and off == 0, btf_struct_ids_match()
will return false. Right now verifier is careful to not call
btf_struct_ids_match in such case, but I wonder if it's better to make
that (common) case also work?

> > > +{
> > > +       const struct btf_type *type;
> > > +       u32 nid;
> > > +       int err;
> > > +
> >
> > mid and nid are terrible names, especially as an input argument name.
> > mid == need_type_id? nid == cur_type_id or something along those
> > lines?
>
> 'mid' was for matching id, 'nid' for nested id ;-)
> need_type_id/cur_type_id sound good

nested I guessed, mid was a mystery to me :))

>
> >
> > > +       do {
> > > +               type = btf_type_by_id(btf_vmlinux, id);
> > > +               if (!type)
> > > +                       return false;
> > > +               err = btf_struct_walk(log, type, off, 1, &nid);
> > > +               if (err < 0)
> > > +                       return false;
> > > +
> > > +               /* We found nested struct object. If it matches
> > > +                * the requested ID, we're done. Otherwise let's
> > > +                * continue the search with offset 0 in the new
> > > +                * type.
> > > +                */
> > > +               if (err == walk_struct && mid == nid)
> > > +                       return true;
> > > +               off = 0;
> > > +               id = nid;
> > > +       } while (err == walk_struct);
> >
> > This seems like a slightly more obvious control flow:
> >
> > again:
> >
> >    ...
> >
> >    if (err != walk_struct)
> >       return false;
>
> ok, and perhaps use in here the switch(err) as in the previous patch?

I think straightforward if is better than switch here, because
anything but walk_struct is not what we expect.

>
> thanks,
> jirka
>
> >
> >    if (mid != nid) {
> >       off = 0;
> >       id = nid;
> >       goto again;
> >    }
> >
> >    return true;
> >
> > > +
> > > +       return false;
> > > +}
> > > +
> > >  int btf_resolve_helper_id(struct bpf_verifier_log *log,
> > >                           const struct bpf_func_proto *fn, int arg)
> > >  {
> >
> > [...]
> >
>

  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-22 21:12 [PATCH v8 bpf-next 00/13] bpf: Add d_path helper Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 01/13] selftests/bpf: Fix resolve_btfids test Jiri Olsa
2020-07-28 20:27   ` Andrii Nakryiko
2020-07-29 20:06     ` Jiri Olsa
2020-07-29 21:38       ` Andrii Nakryiko
2020-07-22 21:12 ` [PATCH v8 bpf-next 02/13] tools resolve_btfids: Add support for set symbols Jiri Olsa
2020-07-28  0:53   ` Andrii Nakryiko
2020-07-28  9:35     ` Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 03/13] bpf: Move btf_resolve_size into __btf_resolve_size Jiri Olsa
2020-07-28 20:29   ` Andrii Nakryiko
2020-07-22 21:12 ` [PATCH v8 bpf-next 04/13] bpf: Add elem_id pointer as argument to __btf_resolve_size Jiri Olsa
2020-07-28 20:30   ` Andrii Nakryiko
2020-07-22 21:12 ` [PATCH v8 bpf-next 05/13] bpf: Add type_id " Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 06/13] bpf: Factor btf_struct_access function Jiri Olsa
2020-07-28 23:27   ` Andrii Nakryiko
2020-07-29 15:59     ` Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 07/13] bpf: Add btf_struct_ids_match function Jiri Olsa
2020-07-28 23:35   ` Andrii Nakryiko
2020-07-29 16:04     ` Jiri Olsa
2020-07-29 17:51       ` Andrii Nakryiko [this message]
2020-07-29 18:55         ` Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 08/13] bpf: Add BTF_SET_START/END macros Jiri Olsa
2020-07-28 19:39   ` Andrii Nakryiko
2020-07-29 11:54     ` Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 09/13] bpf: Add d_path helper Jiri Olsa
2020-07-28 19:47   ` Andrii Nakryiko
2020-07-29 15:54     ` Jiri Olsa
2020-07-29 20:11   ` Al Viro
2020-07-30 10:22     ` Jiri Olsa
2020-07-29 20:17   ` Al Viro
2020-07-30 10:09     ` Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 10/13] bpf: Update .BTF_ids section in btf.rst with sets info Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 11/13] selftests/bpf: Add verifier test for d_path helper Jiri Olsa
2020-07-28 19:49   ` Andrii Nakryiko
2020-07-22 21:12 ` [PATCH v8 bpf-next 12/13] selftests/bpf: Add " Jiri Olsa
2020-07-28 19:53   ` Andrii Nakryiko
2020-07-29 11:25     ` Jiri Olsa
2020-07-22 21:12 ` [PATCH v8 bpf-next 13/13] selftests/bpf: Add set test to resolve_btfids Jiri Olsa
2020-07-28 19:56   ` Andrii Nakryiko
2020-07-29 15:34     ` Jiri Olsa

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