linux-kernel - Re: [PATCH v3 net-next 1/3] perf, bpf: Add BPF support to all perf

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Date:   Fri, 2 Jun 2017 10:06:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <ast@...com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Brendan Gregg <bgregg@...flix.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Teng Qin <qinteng@...com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v3 net-next 1/3] perf, bpf: Add BPF support to all
 perf_event types

On Thu, Jun 01, 2017 at 07:03:34PM -0700, Alexei Starovoitov wrote:
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 172dc8ee0e3b..ab93490d1a00 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -452,39 +452,18 @@ static void bpf_event_entry_free_rcu(struct bpf_event_entry *ee)
>  static void *perf_event_fd_array_get_ptr(struct bpf_map *map,
>  					 struct file *map_file, int fd)
>  {
> -	const struct perf_event_attr *attr;
>  	struct bpf_event_entry *ee;
> -	struct perf_event *event;
>  	struct file *perf_file;
>  
>  	perf_file = perf_event_get(fd);
>  	if (IS_ERR(perf_file))
>  		return perf_file;
>  
> -	event = perf_file->private_data;
> -	ee = ERR_PTR(-EINVAL);
> -
> -	attr = perf_event_attrs(event);
> -	if (IS_ERR(attr) || attr->inherit)
> -		goto err_out;
> -
> -	switch (attr->type) {
> -	case PERF_TYPE_SOFTWARE:
> -		if (attr->config != PERF_COUNT_SW_BPF_OUTPUT)
> -			goto err_out;
> -		/* fall-through */
> -	case PERF_TYPE_RAW:
> -	case PERF_TYPE_HARDWARE:
> -		ee = bpf_event_entry_gen(perf_file, map_file);
> -		if (ee)
> -			return ee;
> -		ee = ERR_PTR(-ENOMEM);
> -		/* fall-through */
> -	default:
> -		break;
> -	}

Would it make sense to call perf_event_read_local() on the events here
in order to weed out the -EOPNOTSUPP  ones?

> +	ee = bpf_event_entry_gen(perf_file, map_file);
> +	if (ee)
> +		return ee;
>  
> -err_out:
> +	ee = ERR_PTR(-ENOMEM);
>  	fput(perf_file);
>  	return ee;
>  }