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

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Date:   Mon, 25 Apr 2022 18:22:37 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     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 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?

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).

>   /**
>    * @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;
>