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

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Message-ID: <871rqziicm.fsf@toke.dk>
Date:   Wed, 12 Feb 2020 22:52:25 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Eelco Chaudron <echaudro@...hat.com>, bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>, Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH bpf-next] libbpf: Add support for dynamic program attach target

Andrii Nakryiko <andrii.nakryiko@...il.com> writes:

> On Wed, Feb 12, 2020 at 5:05 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> 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);
>
> I agree about not specifying section name prefix (e.g., fentry/). But
> disagree that expected attach type (BPF_TRACE_FENTRY) should be part
> of this API. We already have bpf_program__set_expected_attach_type()
> API, no need to duplicate it here.

Ah yes, forgot about that; just keeping that and making this function
name only is fine with me :)

-Toke