linux-kernel - Re: [PATCH v2 2/9] bpf/btf: tracing: Move finding func-proto API and getting func-param API to BTF

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Date:   Wed, 19 Jul 2023 10:09:48 +0800
From:   Donglin Peng <dolinux.peng@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        linux-trace-kernel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        bpf <bpf@...r.kernel.org>, Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH v2 2/9] bpf/btf: tracing: Move finding func-proto API and
 getting func-param API to BTF

On Wed, Jul 19, 2023 at 7:03 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Tue, 18 Jul 2023 10:11:01 -0700
> Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
>
> > On Tue, Jul 18, 2023 at 6:56 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > >
> > > On Tue, 18 Jul 2023 19:44:31 +0900
> > > Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
> > >
> > > > > >  static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,
> > > > > >                                                    bool tracepoint)
> > > > > >  {
> > > > > > +       struct btf *btf = traceprobe_get_btf();
> > > > >
> > > > > I found that traceprobe_get_btf() only returns the vmlinux's btf. But
> > > > > if the function is
> > > > > defined in a kernel module, we should get the module's btf.
> > > > >
> > > >
> > > > Good catch! That should be a separated fix (or improvement?)
> > > > I think it's better to use btf_get() and btf_put(), and pass btf via
> > > > traceprobe_parse_context.
> > >
> > > Hmm, it seems that there is no exposed API to get the module's btf.
> > > Should I use btf_idr and btf_idr_lock directly to find the corresponding
> > > btf? If there isn't yet, I will add it too.
> >
> > There is bpf_find_btf_id.
> > Probably drop 'static' from it and use it.
>
> Thanks! BTW, that API seems to search BTF type info by name. If user want to
> specify a module name, do we need a new API? (Or expand the function to parse
> a module name in given name?)

btf_get_module_btf can be used to get a module's btf, but we have to use
find_module to get the module by its name firstly.

>
> Thank you,
> --
> Masami Hiramatsu (Google) <mhiramat@...nel.org>