linux-kernel - Re: [PATCH v3 2/3] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter

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Message-ID: <55B17139.2070707@plumgrid.com>
Date:	Thu, 23 Jul 2015 15:56:57 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Kaixu Xia <xiakaixu@...wei.com>, davem@...emloft.net,
	acme@...nel.org, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	masami.hiramatsu.pt@...achi.com, jolsa@...nel.org
Cc:	wangnan0@...wei.com, linux-kernel@...r.kernel.org,
	pi3orama@....com, hekuang@...wei.com
Subject: Re: [PATCH v3 2/3] bpf: Implement function bpf_perf_event_read() that
 get the selected hardware PMU conuter

On 7/23/15 2:42 AM, Kaixu Xia wrote:
> According to the perf_event_map_fd and index, the function
> bpf_perf_event_read() can convert the corresponding map
> value to the pointer to struct perf_event and return the
> Hardware PMU counter value.
>
> Signed-off-by: Kaixu Xia <xiakaixu@...wei.com>
...
> +static u64 bpf_perf_event_read(u64 r1, u64 index, u64 r3, u64 r4, u64 r5)
> +{
> +	struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
> +	struct bpf_array *array = container_of(map, struct bpf_array, map);
> +	struct perf_event *event;
> +
> +	if (index >= array->map.max_entries)
> +		return -E2BIG;
> +
> +	event = array->events[index];
> +	if (!event)
> +		return -EBADF;

probably ENOENT makes more sense here.

> +
> +	if (event->state != PERF_EVENT_STATE_ACTIVE)
> +		return -ENOENT;

and -EINVAL here?

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