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Subject: Re: [PATCH v3 2/3] bpf: Implement function bpf_perf_event_read() that
 get the selected hardware PMU conuter
To: Kaixu Xia <xiakaixu@huawei.com>, davem@davemloft.net, acme@kernel.org,
        mingo@redhat.com, a.p.zijlstra@chello.nl,
        masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org
References: <1437644562-84431-1-git-send-email-xiakaixu@huawei.com>
 <1437644562-84431-3-git-send-email-xiakaixu@huawei.com>
Cc: wangnan0@huawei.com, linux-kernel@vger.kernel.org, pi3orama@163.com,
        hekuang@huawei.com
From: Alexei Starovoitov <ast@plumgrid.com>
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Date: Thu, 23 Jul 2015 15:56:57 -0700
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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@huawei.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?