netdev - Re: [PATCH bpf-next 2/3] libbpf: Add support for program extensions

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Date:   Tue, 21 Jan 2020 00:35:43 +0000
From:   Alexei Starovoitov <ast@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Alexei Starovoitov <ast@...nel.org>
CC:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/3] libbpf: Add support for program extensions

On 1/20/20 2:51 PM, Andrii Nakryiko wrote:
> On Fri, Jan 17, 2020 at 4:47 PM Alexei Starovoitov <ast@...nel.org> wrote:
>>
>> Add minimal support for program extensions. bpf_object_open_opts() needs to be
>> called with attach_prog_fd = target_prog_fd and BPF program extension needs to
>> have in .c file section definition like SEC("replace/func_to_be_replaced").
>> libbpf will search for "func_to_be_replaced" in the target_prog_fd's BTF and
>> will pass it in attach_btf_id to the kernel. This approach works for tests, but
>> more compex use case may need to request function name (and attach_btf_id that
>> kernel sees) to be more dynamic. Such API will be added in future patches.
>>
>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>> ---
>>   tools/include/uapi/linux/bpf.h |  1 +
>>   tools/lib/bpf/bpf.c            |  3 ++-
>>   tools/lib/bpf/libbpf.c         | 14 +++++++++++---
>>   tools/lib/bpf/libbpf.h         |  2 ++
>>   tools/lib/bpf/libbpf.map       |  2 ++
>>   tools/lib/bpf/libbpf_probes.c  |  1 +
>>   6 files changed, 19 insertions(+), 4 deletions(-)
>>
> 
> [...]
> 
>>   enum bpf_attach_type
>>   bpf_program__get_expected_attach_type(struct bpf_program *prog)
>> @@ -6265,6 +6269,10 @@ static const struct bpf_sec_def section_defs[] = {
>>                  .expected_attach_type = BPF_TRACE_FEXIT,
>>                  .is_attach_btf = true,
>>                  .attach_fn = attach_trace),
>> +       SEC_DEF("replace/", EXT,
> 
> how about freplace/, similar to fentry/fexit?

I think it's uglier, but fine.

>> +               .expected_attach_type = 0,
> 
> no need, it will be zero, if not specified here

fixed.