Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH bpf-next] bpf: Add bpf_read_raw_record() helper | Date | Fri, 26 Aug 2022 18:09:23 +0000 |
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> On Aug 26, 2022, at 9:33 AM, Namhyung Kim <namhyung@kernel.org> wrote: > > On Thu, Aug 25, 2022 at 10:53 PM Song Liu <song@kernel.org> wrote: >> >> On Thu, Aug 25, 2022 at 10:22 PM Namhyung Kim <namhyung@kernel.org> wrote: >>> >>> On Thu, Aug 25, 2022 at 7:35 PM Song Liu <songliubraving@fb.com> 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
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