linux-kernel - Re: [External] Re: [PATCH bpf-next v2 8/9] libbpf: add support for the multi-link of tracing

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Date: Tue, 12 Mar 2024 09:11:41 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: 梦龙董 <dongmenglong.8@...edance.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>, 
	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@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Sven Schnelle <svens@...ux.ibm.com>, "David S. Miller" <davem@...emloft.net>, 
	David Ahern <dsahern@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	X86 ML <x86@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Quentin Monnet <quentin@...valent.com>, 
	bpf <bpf@...r.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-riscv <linux-riscv@...ts.infradead.org>, linux-s390 <linux-s390@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>, linux-trace-kernel@...r.kernel.org, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [External] Re: [PATCH bpf-next v2 8/9] libbpf: add support for
 the multi-link of tracing

On Mon, Mar 11, 2024 at 7:44 PM 梦龙董 <dongmenglong.8@...edance.com> wrote:
>
> On Tue, Mar 12, 2024 at 9:56 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Mon, Mar 11, 2024 at 2:35 AM Menglong Dong
> > <dongmenglong.8@...edance.com> wrote:
> > >
> > >
> > > -               err = libbpf_find_attach_btf_id(prog, attach_name, &btf_obj_fd, &btf_type_id);
> > > +               name_end = strchr(attach_name, ',');
> > > +               /* for multi-link tracing, use the first target symbol during
> > > +                * loading.
> > > +                */
> > > +               if ((def & SEC_ATTACH_BTF_MULTI) && name_end) {
> > > +                       int len = name_end - attach_name + 1;
> > > +                       char *first_tgt;
> > > +
> > > +                       first_tgt = malloc(len);
> > > +                       if (!first_tgt)
> > > +                               return -ENOMEM;
> > > +                       strncpy(first_tgt, attach_name, len);
> > > +                       first_tgt[len - 1] = '\0';
> > > +                       err = libbpf_find_attach_btf_id(prog, first_tgt, &btf_obj_fd,
> > > +                                                       &btf_type_id);
> > > +                       free(first_tgt);
> > > +               } else {
> > > +                       err = libbpf_find_attach_btf_id(prog, attach_name, &btf_obj_fd,
> > > +                                                       &btf_type_id);
> > > +               }
> >
> > Pls use glob_match the way [ku]probe multi are doing
> > instead of exact match.
>
> Hello,
>
> I'm a little suspecting the effect of glob_match. I seldom found
> the use case that the kernel functions which we want to trace
> have the same naming pattern. And the exact match seems more
> useful.
>
> Can we use both exact and glob match here?

exact is a subset of glob_match.
Pls follow the pattern that[ku]probe multi established
in terms of user interface expectations.