linux-kernel - Re: [PATCH v1 2/7] bpf: Add bpf_perf_event_aux

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Message-ID: <80f412f1-a060-463b-9034-3128906e6929@linux.dev>
Date: Mon, 16 Dec 2024 09:21:15 -0800
From: Yonghong Song <yonghong.song@...ux.dev>
To: Leo Yan <leo.yan@....com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Adrian Hunter <adrian.hunter@...el.com>, Namhyung Kim <namhyung@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 James Clark <james.clark@...aro.org>, "Liang, Kan"
 <kan.liang@...ux.intel.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Matt Bobrowski <mattbobrowski@...gle.com>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 bpf@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach <mike.leach@...aro.org>
Subject: Re: [PATCH v1 2/7] bpf: Add bpf_perf_event_aux_pause kfunc




On 12/15/24 11:34 AM, Leo Yan wrote:
> The bpf_perf_event_aux_pause kfunc will be used to control the Perf AUX
> area to pause or resume.
>
> An example use-case is attaching eBPF to Ftrace tracepoints.  When a
> tracepoint is hit, the associated eBPF program will be executed.  The
> eBPF program can invoke bpf_perf_event_aux_pause() to pause or resume
> AUX trace.  This is useful for fine-grained tracing by combining
> Perf and eBPF.
>
> This commit implements the bpf_perf_event_aux_pause kfunc, and make it
> pass the eBPF verifier.

The subject and commit message mentions to implement a kfunc,
but actually you implemented a uapi helper. Please implement a kfunc
instead (searching __bpf_kfunc in kernel/bpf directory).

>
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>   include/uapi/linux/bpf.h | 21 ++++++++++++++++
>   kernel/bpf/verifier.c    |  2 ++
>   kernel/trace/bpf_trace.c | 52 ++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 75 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4162afc6b5d0..678278c91ce2 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5795,6 +5795,26 @@ union bpf_attr {
>    *		0 on success.
>    *
>    *		**-ENOENT** if the bpf_local_storage cannot be found.
> + *
> + * long bpf_perf_event_aux_pause(struct bpf_map *map, u64 flags, u32 pause)
> + *	Description
> + *		Pause or resume an AUX area trace associated to the perf event.
> + *
> + *		The *flags* argument is specified as the key value for
> + *		retrieving event pointer from the passed *map*.
> + *
> + *		The *pause* argument controls AUX trace pause or resume.
> + *		Non-zero values (true) are to pause the AUX trace and the zero
> + *		value (false) is for re-enabling the AUX trace.
> + *	Return
> + *		0 on success.
> + *
> + *		**-ENOENT** if not found event in the events map.
> + *
> + *		**-E2BIG** if the event index passed in the *flags* parameter
> + *		is out-of-range of the map.
> + *
> + *		**-EINVAL** if the flags passed is an invalid value.
>    */
>   #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
>   	FN(unspec, 0, ##ctx)				\
> @@ -6009,6 +6029,7 @@ union bpf_attr {
>   	FN(user_ringbuf_drain, 209, ##ctx)		\
>   	FN(cgrp_storage_get, 210, ##ctx)		\
>   	FN(cgrp_storage_delete, 211, ##ctx)		\
> +	FN(perf_event_aux_pause, 212, ##ctx)		\
>   	/* */
>   
>   /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
>
[...]