netdev - Re: [PATCH perf/core 1/5] libbpf: Add bpf_program__set

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Date:   Tue, 26 Apr 2022 08:19:05 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        linux-perf-users@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH perf/core 1/5] libbpf: Add bpf_program__set_insns function

On Mon, Apr 25, 2022 at 06:22:37PM +0200, Daniel Borkmann wrote:
> On 4/22/22 12:00 PM, Jiri Olsa wrote:
> > Adding bpf_program__set_insns that allows to set new
> > instructions for program.
> > 
> > Also moving bpf_program__attach_kprobe_multi_opts on
> > the proper name sorted place in map file.
> > 
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >   tools/lib/bpf/libbpf.c   |  8 ++++++++
> >   tools/lib/bpf/libbpf.h   | 12 ++++++++++++
> >   tools/lib/bpf/libbpf.map |  3 ++-
> >   3 files changed, 22 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 809fe209cdcc..284790d81c1b 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -8457,6 +8457,14 @@ size_t bpf_program__insn_cnt(const struct bpf_program *prog)
> >   	return prog->insns_cnt;
> >   }
> > +void bpf_program__set_insns(struct bpf_program *prog,
> > +			    struct bpf_insn *insns, size_t insns_cnt)
> > +{
> > +	free(prog->insns);
> > +	prog->insns = insns;
> > +	prog->insns_cnt = insns_cnt;
> > +}
> > +
> >   int bpf_program__set_prep(struct bpf_program *prog, int nr_instances,
> >   			  bpf_program_prep_t prep)
> >   {
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index 05dde85e19a6..b31ad58d335f 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -323,6 +323,18 @@ struct bpf_insn;
> >    * different.
> >    */
> >   LIBBPF_API const struct bpf_insn *bpf_program__insns(const struct bpf_program *prog);
> > +
> > +/**
> > + * @brief **bpf_program__set_insns()** can set BPF program's underlying
> > + * BPF instructions.
> > + * @param prog BPF program for which to return instructions
> > + * @param insn a pointer to an array of BPF instructions
> > + * @param insns_cnt number of `struct bpf_insn`'s that form
> > + * specified BPF program
> > + */
> > +LIBBPF_API void bpf_program__set_insns(struct bpf_program *prog,
> > +				       struct bpf_insn *insns, size_t insns_cnt);
> > +
> 
> Iiuc, patch 2 should be squashed into this one given they logically belong to the
> same change?

right, that's probably better

> 
> Fwiw, I think the API description should be elaborated a bit more, in particular that
> the passed-in insns need to be from allocated dynamic memory which is later on passed
> to free(), and maybe also constraints at which point in time bpf_program__set_insns()
> may be called.. (as well as high-level description on potential use cases e.g. around
> patch 4).

ok, will add that

thanks,
jirka

> 
> >   /**
> >    * @brief **bpf_program__insn_cnt()** returns number of `struct bpf_insn`'s
> >    * that form specified BPF program.
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index dd35ee58bfaa..afa10d24ab41 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -444,7 +444,8 @@ LIBBPF_0.8.0 {
> >   	global:
> >   		bpf_object__destroy_subskeleton;
> >   		bpf_object__open_subskeleton;
> > +		bpf_program__attach_kprobe_multi_opts;
> > +		bpf_program__set_insns;
> >   		libbpf_register_prog_handler;
> >   		libbpf_unregister_prog_handler;
> > -		bpf_program__attach_kprobe_multi_opts;
> >   } LIBBPF_0.7.0;
> > 
>