Re: [PATCH bpf-next] bpf: Add bpf_read_raw_record() helper

[Song Liu]

> On Aug 26, 2022, at 12:30 PM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> 
> On Fri, Aug 26, 2022 at 11:45 AM Song Liu <songliubraving@xxxxxx> wrote:
> 
>>> And actually, we can just read ctx->data and get the raw record,
>>> right..?
>> 
>> Played with this for a little bit. ctx->data appears to be not
>> reliable sometimes. I guess (not 100% sure) this is because we
>> call bpf program before event->orig_overflow_handler. We can
>> probably add a flag to specify we want to call orig_overflow_handler
>> first.
> 
> I'm not sure.  The sample_data should be provided by the caller
> of perf_event_overflow.  So I guess the bpf program should see
> a valid ctx->data.

Let's dig into this. Maybe we need some small changes in 
pe_prog_convert_ctx_access. 

> Also I want to control calling the orig_overflow_handler based
> on the return value of the BPF program.  So calling the orig
> handler before BPF won't work for me. :)

Interesting. Could you share more information about the use case?

Thanks,
Song