netdev - Re: [PATCH 1/1] tools/dtrace: initial implementation of DTrace

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Message-ID: <20190704130509.GO3402@hirez.programming.kicks-ass.net>
Date:   Thu, 4 Jul 2019 15:05:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kris Van Hees <kris.van.hees@...cle.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        dtrace-devel@....oracle.com, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, mhiramat@...nel.org, acme@...nel.org,
        ast@...nel.org, daniel@...earbox.net, Chris Mason <clm@...com>
Subject: Re: [PATCH 1/1] tools/dtrace: initial implementation of DTrace

On Wed, Jul 03, 2019 at 08:14:30PM -0700, Kris Van Hees wrote:
> +int dt_bpf_attach(int event_id, int bpf_fd)
> +{
> +	int			event_fd;
> +	int			rc;
> +	struct perf_event_attr	attr = {};
> +
> +	attr.type = PERF_TYPE_TRACEPOINT;
> +	attr.sample_type = PERF_SAMPLE_RAW;
> +	attr.sample_period = 1;
> +	attr.wakeup_events = 1;
> +	attr.config = event_id;
> +
> +	/* Register the event (based on its id), and obtain a fd. */
> +	event_fd = perf_event_open(&attr, -1, 0, -1, 0);
> +	if (event_fd < 0) {
> +		perror("sys_perf_event_open");
> +		return -1;
> +	}
> +
> +	/* Enable the probe. */
> +	rc = ioctl(event_fd, PERF_EVENT_IOC_ENABLE, 0);

AFAICT you didn't use attr.disabled = 1, so this IOC_ENABLE is
completely superfluous.

> +	if (rc < 0) {
> +		perror("PERF_EVENT_IOC_ENABLE");
> +		return -1;
> +	}
> +
> +	/* Associate the BPF program with the event. */
> +	rc = ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, bpf_fd);
> +	if (rc < 0) {
> +		perror("PERF_EVENT_IOC_SET_BPF");
> +		return -1;
> +	}
> +
> +	return 0;
> +}