netdev - Re: [PATCH bpf-next] libbpf: Add support for dynamic program attach target

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Message-ID: <874kvwhs6u.fsf@toke.dk>
Date:   Wed, 12 Feb 2020 14:05:13 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Eelco Chaudron <echaudro@...hat.com>, bpf@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, kafai@...com, songliubraving@...com,
        yhs@...com, andriin@...com
Subject: Re: [PATCH bpf-next] libbpf: Add support for dynamic program attach target

Eelco Chaudron <echaudro@...hat.com> writes:

> Currently when you want to attach a trace program to a bpf program
> the section name needs to match the tracepoint/function semantics.
>
> However the addition of the bpf_program__set_attach_target() API
> allows you to specify the tracepoint/function dynamically.
>
> The call flow would look something like this:
>
>   xdp_fd = bpf_prog_get_fd_by_id(id);
>   trace_obj = bpf_object__open_file("func.o", NULL);
>   prog = bpf_object__find_program_by_title(trace_obj,
>                                            "fentry/myfunc");
>   bpf_program__set_attach_target(prog, xdp_fd,
>                                  "fentry/xdpfilt_blk_all");

I think it would be better to have the attach type as a separate arg
instead of encoding it in the function name. I.e., rather:

   bpf_program__set_attach_target(prog, xdp_fd,
                                  "xdpfilt_blk_all", BPF_TRACE_FENTRY);

-Toke