netdev - Re: [PATCH bpf-next 4/7] libbpf: Add support to attach to fentry/fexit tracing progs

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Date:   Tue, 5 Nov 2019 23:17:59 +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>,
        Peter Ziljstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 4/7] libbpf: Add support to attach to
 fentry/fexit tracing progs

On 11/5/19 1:17 PM, Andrii Nakryiko wrote:
> On Sat, Nov 2, 2019 at 3:03 PM Alexei Starovoitov <ast@...nel.org> wrote:
>>
>> Teach libbpf to recognize tracing programs types and attach them to
>> fentry/fexit.
>>
>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>> ---
>>   tools/include/uapi/linux/bpf.h |  2 ++
>>   tools/lib/bpf/libbpf.c         | 55 +++++++++++++++++++++++++++++-----
>>   tools/lib/bpf/libbpf.h         |  2 ++
>>   tools/lib/bpf/libbpf.map       |  1 +
>>   4 files changed, 53 insertions(+), 7 deletions(-)
>>
>> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
>> index df6809a76404..69c200e6e696 100644
>> --- a/tools/include/uapi/linux/bpf.h
>> +++ b/tools/include/uapi/linux/bpf.h
>> @@ -201,6 +201,8 @@ enum bpf_attach_type {
>>          BPF_CGROUP_GETSOCKOPT,
>>          BPF_CGROUP_SETSOCKOPT,
>>          BPF_TRACE_RAW_TP,
>> +       BPF_TRACE_FENTRY,
>> +       BPF_TRACE_FEXIT,
>>          __MAX_BPF_ATTACH_TYPE
>>   };
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 7aa2a2a22cef..03e784f36dd9 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -3744,7 +3744,7 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
>>          return 0;
>>   }
>>
>> -static int libbpf_attach_btf_id_by_name(const char *name, __u32 *btf_id);
>> +static int libbpf_attach_btf_id_by_name(const char *name, __u32 *btf_id, bool raw_tp);
> 
> Bools are hard to follow in code, why not just passing full
> attach_type instead? It will also be more future-proof, if we need
> another trick, similar to "bpf_trace_" prefix for raw_tp?
> 
> Also, I have a mild preference for having output arguments to be the
> very last in the argument list. Do you mind reordering so thar bool
> raw_tp is second?

Agree on both counts. Spotted another small nit in this function
while testing corner cases.
Will fix this and feedback to 5/7, 7/7 in the next version.