Commit 4bebdc7a authored by Yonghong Song's avatar Yonghong Song Committed by David S. Miller
Browse files

bpf: add helper bpf_perf_prog_read_value 



This patch adds helper bpf_perf_prog_read_cvalue for perf event based bpf
programs, to read event counter and enabled/running time.
The enabled/running time is accumulated since the perf event open.

The typical use case for perf event based bpf program is to attach itself
to a single event. In such cases, if it is desirable to get scaling factor
between two bpf invocations, users can can save the time values in a map,
and use the value from the map and the current value to calculate
the scaling factor.

Signed-off-by: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@fb.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 020a32d9

include/uapi/linux/bpf.h

+9 −1
Original line number Diff line number Diff line
@@ -649,6 +649,13 @@ union bpf_attr { 
 *     @buf: buf to fill

 *     @buf_size: size of the buf

 *     Return: 0 on success or negative error code

 *

 * int bpf_perf_prog_read_value(ctx, buf, buf_size)

 *     read perf prog attached perf event counter and enabled/running time

 *     @ctx: pointer to ctx

 *     @buf: buf to fill

 *     @buf_size: size of the buf

 *     Return : 0 on success or negative error code

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -706,7 +713,8 @@ union bpf_attr { 
	FN(sk_redirect_map),		\

	FN(sock_map_update),		\

	FN(xdp_adjust_meta),		\

	FN(perf_event_read_value),

	FN(perf_event_read_value),	\

	FN(perf_prog_read_value),



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

 * function eBPF program intends to call

kernel/trace/bpf_trace.c

+28 −0
Original line number Diff line number Diff line
@@ -613,6 +613,32 @@ static const struct bpf_func_proto bpf_get_stackid_proto_tp = { 
	.arg3_type	= ARG_ANYTHING,

};



BPF_CALL_3(bpf_perf_prog_read_value_tp, struct bpf_perf_event_data_kern *, ctx,

	   struct bpf_perf_event_value *, buf, u32, size)

{

	int err = -EINVAL;



	if (unlikely(size != sizeof(struct bpf_perf_event_value)))

		goto clear;

	err = perf_event_read_local(ctx->event, &buf->counter, &buf->enabled,

				    &buf->running);

	if (unlikely(err))

		goto clear;

	return 0;

clear:

	memset(buf, 0, size);

	return err;

}



static const struct bpf_func_proto bpf_perf_prog_read_value_proto_tp = {

         .func           = bpf_perf_prog_read_value_tp,

         .gpl_only       = true,

         .ret_type       = RET_INTEGER,

         .arg1_type      = ARG_PTR_TO_CTX,

         .arg2_type      = ARG_PTR_TO_UNINIT_MEM,

         .arg3_type      = ARG_CONST_SIZE,

};



static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)

{

	switch (func_id) {
@@ -620,6 +646,8 @@ static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id) 
		return &bpf_perf_event_output_proto_tp;

	case BPF_FUNC_get_stackid:

		return &bpf_get_stackid_proto_tp;

	case BPF_FUNC_perf_prog_read_value:

		return &bpf_perf_prog_read_value_proto_tp;

	default:

		return tracing_func_proto(func_id);

	}

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