> On Aug 26, 2022, at 9:33 AM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Thu, Aug 25, 2022 at 10:53 PM Song Liu <song@xxxxxxxxxx> wrote:
>>
>> On Thu, Aug 25, 2022 at 10:22 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>>>
>>> On Thu, Aug 25, 2022 at 7:35 PM Song Liu <songliubraving@xxxxxx> wrote:
>>>> Actually, since we are on this, can we make it more generic, and handle
>>>> all possible PERF_SAMPLE_* (in enum perf_event_sample_format)? Something
>>>> like:
>>>>
>>>> long bpf_perf_event_read_sample(void *ctx, void *buf, u64 size, u64 flags);
>>>>
>>>> WDYT Namhyung?
>>>
>>> Do you mean reading the whole sample data at once?
>>> Then it needs to parse the sample data format properly
>>> which is non trivial due to a number of variable length
>>> fields like callchains and branch stack, etc.
>>>
>>> Also I'm afraid I might need event configuration info
>>> other than sample data like attr.type, attr.config,
>>> attr.sample_type and so on.
>>>
>>> Hmm.. maybe we can add it to the ctx directly like ctx.attr_type?
>>
>> The user should have access to the perf_event_attr used to
>> create the event. This is also available in ctx->event->attr.
>
> Do you mean from BPF? I'd like to have a generic BPF program
> that can handle various filtering according to the command line
> arguments. I'm not sure but it might do something differently
> for each event based on the attr settings.
Yeah, we can access perf_event_attr from BPF program. Note that
the ctx for perf_event bpf program is struct bpf_perf_event_data_kern:
SEC("perf_event")
int perf_e(struct bpf_perf_event_data_kern *ctx)
{
...
}
struct bpf_perf_event_data_kern {
bpf_user_pt_regs_t *regs;
struct perf_sample_data *data;
struct perf_event *event;
};
Alternatively, we can also have bpf user space configure the BPF
program via a few knobs.
And actually, we can just read ctx->data and get the raw record,
right..?
Thanks,
Song
