linux-kernel - Re: [PATCH v3 2/3] perf: Userspace event

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Date:	Tue, 04 Nov 2014 15:33:19 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Pawel Moll <pawel.moll@....com>
Cc:	Richard Cochran <richardcochran@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Christopher Covington <cov@...eaurora.org>,
	David Ahern <dsahern@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tomeu Vizoso <tomeu@...euvizoso.net>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Pawel Moll <mail@...elmoll.com>
Subject: Re: [PATCH v3 2/3] perf: Userspace event

Hi Pawel,

On Tue,  4 Nov 2014 00:28:37 +0000, Pawel Moll wrote:
> +	/*
> +	 * Data in userspace event record is transparent for the kernel
> +	 *
> +	 * Userspace perf tool code maintains a list of known types with
> +	 * reference implementations of parsers for the data field.
> +	 *
> +	 * Overall size of the record (including type and size fields)
> +	 * is always aligned to 8 bytes by adding padding after the data.
> +	 *
> +	 * struct {
> +	 *	struct perf_event_header	header;
> +	 *	u32				type;
> +	 *	u32				size;

The struct perf_event_header also has 'size' field and it has the entire
length of the record so it's redundant.  Also there's 'misc' field in the
perf_event_header and I guess it can be used as 'type' info as it's
mostly for cpumode and we are in user mode by definition.

Thanks,
Namhyung


> +	 *	char				data[size];
> +	 *	char				__padding[-size & 7];
> +	 * 	struct sample_id		sample_id;
> +	 * };
> +	 */
> +	PERF_RECORD_UEVENT			= 11,
> +
>  	PERF_RECORD_MAX,			/* non-ABI */
>  };
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