On Fri, Aug 26, 2022 at 11:09 AM Song Liu <songliubraving@xxxxxx> wrote: > > > > > 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; > }; I didn't know that it's allowed to access the kernel data directly. For some reason, I thought it should use fields in bpf_event_event_data only, like sample_period and addr. And the verifier will convert the access to them according to pe_prog_convert_ctx_access(). > > 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..? If it's possible, sure, it'd be more powerful. Thanks, Namhyung