netdev - Re: [PATCH v6 2/4] bpf: Add new bpf map type to store the pointer to struct perf

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Date:	Wed, 5 Aug 2015 11:39:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kaixu Xia <xiakaixu@...wei.com>
Cc:	ast@...mgrid.com, davem@...emloft.net, acme@...nel.org,
	mingo@...hat.com, masami.hiramatsu.pt@...achi.com,
	jolsa@...nel.org, daniel@...earbox.net, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com, hekuang@...wei.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH v6 2/4] bpf: Add new bpf map type to store the pointer to
 struct perf_event

On Tue, Aug 04, 2015 at 08:58:14AM +0000, Kaixu Xia wrote:

> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 2027809..81fc99e 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -641,6 +641,8 @@ extern int perf_event_init_task(struct task_struct *child);
>  extern void perf_event_exit_task(struct task_struct *child);
>  extern void perf_event_free_task(struct task_struct *task);
>  extern void perf_event_delayed_put(struct task_struct *task);
> +extern struct perf_event *perf_event_get(unsigned int fd);
> +extern struct perf_event_attr *perf_event_attrs(struct perf_event *event);

const struct perf_event_attr *perf_event_attrs();


> +static void *perf_event_fd_array_get_ptr(struct bpf_map *map, int fd)
> +{
> +	struct perf_event *event;
> +	struct perf_event_attr *attr;

Also const

> +
> +	event = perf_event_get(fd);
> +	if (IS_ERR(event))
> +		return event;
> +
> +	attr = perf_event_attrs(event);
> +	if (IS_ERR(attr))
> +		return attr;
> +
> +	if (attr->type != PERF_TYPE_RAW &&
> +	    attr->type != PERF_TYPE_HARDWARE) {
> +		perf_event_release_kernel(event);
> +		return ERR_PTR(-EINVAL);
> +	}
> +	return event;
> +}

> +struct perf_event_attr *perf_event_attrs(struct perf_event *event)

Also const

> +{
> +	if (!event)
> +		return ERR_PTR(-EINVAL);
> +
> +	return &event->attr;
> +}

It doesn't make sense (ever) to allow users of this function to change
attributes of the event, inspecting them is fine.
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