Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 3 Nov 2022 14:21:26 -0700 | Subject | Re: [PATCH bpf-next 2/3] bpf: Add bpf_perf_event_read_sample() helper | From | Yonghong Song <> |
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On 11/3/22 1:55 PM, Song Liu wrote: > > >> On Nov 3, 2022, at 12:45 PM, Yonghong Song <yhs@meta.com> wrote: >> >> >> >> On 11/1/22 3:02 AM, Jiri Olsa wrote: >>> On Mon, Oct 31, 2022 at 10:23:39PM -0700, Namhyung Kim wrote: >>>> The bpf_perf_event_read_sample() helper is to get the specified sample >>>> data (by using PERF_SAMPLE_* flag in the argument) from BPF to make a >>>> decision for filtering on samples. Currently PERF_SAMPLE_IP and >>>> PERF_SAMPLE_DATA flags are supported only. >>>> >>>> Signed-off-by: Namhyung Kim <namhyung@kernel.org> >>>> --- >>>> include/uapi/linux/bpf.h | 23 ++++++++++++++++ >>>> kernel/trace/bpf_trace.c | 49 ++++++++++++++++++++++++++++++++++ >>>> tools/include/uapi/linux/bpf.h | 23 ++++++++++++++++ >>>> 3 files changed, 95 insertions(+) >>>> >>>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >>>> index 94659f6b3395..cba501de9373 100644 >>>> --- a/include/uapi/linux/bpf.h >>>> +++ b/include/uapi/linux/bpf.h >>>> @@ -5481,6 +5481,28 @@ union bpf_attr { >>>> * 0 on success. >>>> * >>>> * **-ENOENT** if the bpf_local_storage cannot be found. >>>> + * >>>> + * long bpf_perf_event_read_sample(struct bpf_perf_event_data *ctx, void *buf, u32 size, u64 sample_flags) >>>> + * Description >>>> + * For an eBPF program attached to a perf event, retrieve the >>>> + * sample data associated to *ctx* and store it in the buffer >>>> + * pointed by *buf* up to size *size* bytes. >>>> + * >>>> + * The *sample_flags* should contain a single value in the >>>> + * **enum perf_event_sample_format**. >>>> + * Return >>>> + * On success, number of bytes written to *buf*. On error, a >>>> + * negative value. >>>> + * >>>> + * The *buf* can be set to **NULL** to return the number of bytes >>>> + * required to store the requested sample data. >>>> + * >>>> + * **-EINVAL** if *sample_flags* is not a PERF_SAMPLE_* flag. >>>> + * >>>> + * **-ENOENT** if the associated perf event doesn't have the data. >>>> + * >>>> + * **-ENOSYS** if system doesn't support the sample data to be >>>> + * retrieved. >>>> */ >>>> #define ___BPF_FUNC_MAPPER(FN, ctx...) \ >>>> FN(unspec, 0, ##ctx) \ >>>> @@ -5695,6 +5717,7 @@ union bpf_attr { >>>> FN(user_ringbuf_drain, 209, ##ctx) \ >>>> FN(cgrp_storage_get, 210, ##ctx) \ >>>> FN(cgrp_storage_delete, 211, ##ctx) \ >>>> + FN(perf_event_read_sample, 212, ##ctx) \ >>>> /* */ >>>> /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't >>>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c >>>> index ce0228c72a93..befd937afa3c 100644 >>>> --- a/kernel/trace/bpf_trace.c >>>> +++ b/kernel/trace/bpf_trace.c >>>> @@ -28,6 +28,7 @@ >>>> #include <uapi/linux/bpf.h> >>>> #include <uapi/linux/btf.h> >>>> +#include <uapi/linux/perf_event.h> >>>> #include <asm/tlb.h> >>>> @@ -1743,6 +1744,52 @@ static const struct bpf_func_proto bpf_read_branch_records_proto = { >>>> .arg4_type = ARG_ANYTHING, >>>> }; >>>> +BPF_CALL_4(bpf_perf_event_read_sample, struct bpf_perf_event_data_kern *, ctx, >>>> + void *, buf, u32, size, u64, flags) >>>> +{ >>> I wonder we could add perf_btf (like we have tp_btf) program type that >>> could access ctx->data directly without helpers >> >> Martin and I have discussed an idea to introduce a generic helper like >> bpf_get_kern_ctx(void *ctx) >> Given a context, the helper will return a PTR_TO_BTF_ID representing the >> corresponding kernel ctx. So in the above example, user could call >> >> struct bpf_perf_event_data_kern *kctx = bpf_get_kern_ctx(ctx); >> ... > > This is an interesting idea! > >> To implement bpf_get_kern_ctx helper, the verifier can find the type >> of the context and provide a hidden btf_id as the second parameter of >> the actual kernel helper function like >> bpf_get_kern_ctx(ctx) { >> return ctx; >> } >> /* based on ctx_btf_id, find kctx_btf_id and return it to verifier */ > > I think we will need a map of ctx_btf_id => kctx_btf_id. Shall we somehow > expose this to the user?
Yes, inside the kernel we need ctx_btf_id -> kctx_btf_id mapping. Good question. We might not want to this mapping as a stable API. So using kfunc might be more appropriate.
> > Thanks, > Song > > >> The bpf_get_kern_ctx helper can be inlined as well. > >
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