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

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Message-ID: <62B507DD-104D-4006-9FF0-204AD23B1505@redhat.com>
Date:   Thu, 13 Feb 2020 15:41:06 +0100
From:   "Eelco Chaudron" <echaudro@...hat.com>
To:     "Toke Høiland-Jørgensen" <toke@...hat.com>
Cc:     "Andrii Nakryiko" <andrii.nakryiko@...il.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



On 12 Feb 2020, at 22:52, Toke Høiland-Jørgensen wrote:

> 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/Andrii,

Thanks for the feedback, will send out a v2 soon.

//Eelco