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Date:   Wed, 23 Sep 2020 21:59:28 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "Kernel Team" <Kernel-team@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: enable BPF_PROG_TEST_RUN for
 raw_tracepoint



> On Sep 23, 2020, at 12:36 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> 
> On Wed, Sep 23, 2020 at 9:54 AM Song Liu <songliubraving@...com> wrote:
>> 
>> Add .test_run for raw_tracepoint. Also, introduce a new feature that runs
>> the target program on a specific CPU. This is achieved by a new flag in
>> bpf_attr.test, cpu_plus. For compatibility, cpu_plus == 0 means run the
>> program on current cpu, cpu_plus > 0 means run the program on cpu with id
>> (cpu_plus - 1). This feature is needed for BPF programs that handle
>> perf_event and other percpu resources, as the program can access these
>> resource locally.
>> 
>> Acked-by: John Fastabend <john.fastabend@...il.com>
>> Signed-off-by: Song Liu <songliubraving@...com>
>> ---
>> include/linux/bpf.h            |  3 ++
>> include/uapi/linux/bpf.h       |  5 ++
>> kernel/bpf/syscall.c           |  2 +-
>> kernel/trace/bpf_trace.c       |  1 +
>> net/bpf/test_run.c             | 88 ++++++++++++++++++++++++++++++++++
>> tools/include/uapi/linux/bpf.h |  5 ++
>> 6 files changed, 103 insertions(+), 1 deletion(-)
>> 
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index d7c5a6ed87e30..23758c282eb4b 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1376,6 +1376,9 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
>> int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
>>                                     const union bpf_attr *kattr,
>>                                     union bpf_attr __user *uattr);
>> +int bpf_prog_test_run_raw_tp(struct bpf_prog *prog,
>> +                            const union bpf_attr *kattr,
>> +                            union bpf_attr __user *uattr);
>> bool btf_ctx_access(int off, int size, enum bpf_access_type type,
>>                    const struct bpf_prog *prog,
>>                    struct bpf_insn_access_aux *info);
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index a22812561064a..89acf41913e70 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -566,6 +566,11 @@ union bpf_attr {
>>                                                 */
>>                __aligned_u64   ctx_in;
>>                __aligned_u64   ctx_out;
>> +               __u32           cpu_plus;       /* run this program on cpu
>> +                                                * (cpu_plus - 1).
>> +                                                * If cpu_plus == 0, run on
>> +                                                * current cpu.
>> +                                                */
> 
> the "_plus" part of the name is so confusing, just as off-by-one
> semantics.. Why not do what we do with BPF_PROG_ATTACH? I.e., we have
> flags field, and if the specific bit is set then we use extra field's
> value. In this case, you'd have:
> 
> __u32 flags;
> __u32 cpu; /* naturally 0-based */
> 
> cpu indexing will be natural without any offsets, and you'll have
> something like BPF_PROG_TEST_CPU flag, that needs to be specified.
> This will work well with backward/forward compatibility. If you need a
> special "current CPU" mode, you can achieve that by not specifying
> BPF_PROG_TEST_CPU flag, or we can designate (__u32)-1 as a special
> "current CPU" value.
> 
> WDYT?

Yes, we can add a flag here. If there was already a flags field in
bpf_attr.test, I would have gone that way in the first place. 

Thanks,
Song

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