Re: [PATCH bpf-next 1/2] bpf/perf: Call perf_prepare_sample() before bpf_prog_run()

Daniel Borkmann
2022-12-22T13:18:22Z

On 12/22/22 1:55 PM, Peter Zijlstra wrote:
> On Tue, Dec 20, 2022 at 02:01:43PM -0800, Namhyung Kim wrote:
>> When the BPF program calls bpf_cast_to_kern_ctx(), it assumes the program will
>> access perf sample data directly and call perf_prepare_sample() to make sure
>> the sample data is populated.
>
> I don't understand a word of this :/ What are you doing and why?

Yeah, above commit message is too terse and unclear. Also, not following where
this assumption comes from; bpf_cast_to_kern_ctx() can be used elsewhere, too,
not just tracing. Recent example from CI side can be found [0].

Thanks,
Daniel

[0] bpf tree, 70a00e2f1dba ("selftests/bpf: Test bpf_skb_adjust_room on CHECKSUM_PARTIAL")