linux-kernel - Re: [PATCH 4/7] tracing: add format file to describe event struct fields

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Date:	Mon, 2 Mar 2009 13:11:09 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, peterz@...radead.org,
	fweisbec@...il.com, tytso@....edu, compudj@...stal.dyndns.org,
	tzanussi@...il.com, mhiramat@...hat.com,
	kosaki.motohiro@...fujitsu.com, jbaron@...hat.com, fche@...hat.com,
	acme@...hat.com, srostedt@...hat.com
Subject: Re: [PATCH 4/7] tracing: add format file to describe event struct
 fields

On Mon, 02 Mar 2009 15:29:29 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <srostedt@...hat.com>
> 
> This patch adds the "format" file to the trace point event directory.
> This is based off of work by Tom Zanussi, in which a file is exported
> to be tread from user land such that a user space app may read the

s/tread/read/

> binary record stored in the ring buffer.
>
> ...
>
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -3,6 +3,9 @@
>   *
>   * Copyright (C) 2008 Red Hat Inc, Steven Rostedt <srostedt@...hat.com>
>   *
> + *  - Added format output of fields of the trace point.
> + *    This was based off of work by Tom Zanussi <tzanussi@...il.com>.

ick.  "based on"

> + *
>   */
>  
>  #include <linux/debugfs.h>
> @@ -444,6 +447,42 @@ event_available_types_read(struct file *filp, char __user *ubuf, size_t cnt,
>  	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
>  }
>  
> +static ssize_t
> +event_format_read(struct file *filp, char __user *ubuf, size_t cnt,
> +		  loff_t *ppos)
> +{
> +	struct ftrace_event_call *call = filp->private_data;
> +	struct trace_seq *s;
> +	char *buf;
> +	int r;
> +
> +	s = kmalloc(sizeof(*s), GFP_KERNEL);
> +	if (!s)
> +		return -ENOMEM;
> +
> +	trace_seq_init(s);
> +
> +	if (*ppos)
> +		return 0;

Someone get this man a bucket!

> +	r = call->show_format(s);
> +	if (!r) {
> +		/*
> +		 * ug!  The format output is bigger than a PAGE!!
> +		 */
> +		buf = "FORMAT TOO BIG\n";
> +		r = simple_read_from_buffer(ubuf, cnt, ppos,
> +					      buf, strlen(buf));
> +		goto out;
> +	}
> +
> +	r = simple_read_from_buffer(ubuf, cnt, ppos,
> +				    s->buffer, s->len);
> + out:
> +	kfree(s);
> +	return r;
> +}

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