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Date: Sat, 27 Mar 2010 04:14:57 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Tom Zanussi <tzanussi@gmail.com>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, rostedt@goodmis.org,
       k-keiichi@bx.jp.nec.com
Subject: Re: [RFC PATCH 2/7] perf: add pipe-specific header read/write and
	event processing code
Message-ID: <20100327031455.GN7166@nowhere>
References: <1267599929-8310-1-git-send-email-tzanussi@gmail.com> <1267599929-8310-3-git-send-email-tzanussi@gmail.com>
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On Wed, Mar 03, 2010 at 01:05:24AM -0600, Tom Zanussi wrote:
>  
> +int perf_header__write_pipe(struct perf_header *self, int fd)
> +{
> +	struct perf_file_header_pipe f_header;
> +	int err;
> +
> +	f_header = (struct perf_file_header_pipe){
> +		.magic	   = PERF_MAGIC,
> +		.size	   = sizeof(f_header),
> +	};
> +
> +	err = do_write(fd, &f_header, sizeof(f_header));
> +	if (err < 0) {
> +		pr_debug("failed to write perf pipe header\n");
> +		return err;
> +	}
> +
> +	self->frozen = 1;
> +	return 0;
> +}



I actually wonder why you bother with a header in the pipe mode,
since it only contains MAGIC and its size.