tracing/events: add trace-events-sample

	help

	  This build tracepoints example modules.

config SAMPLE_TRACE_EVENTS

	tristate "Build trace_events examples"

	depends on EVENT_TRACING

	default m

	help

	  This build trace event example modules.

config SAMPLE_KOBJECT

	tristate "Build kobject examples"

	help

# Makefile for Linux samples code

obj-$(CONFIG_SAMPLES)	+= markers/ kobject/ kprobes/ tracepoints/

obj-$(CONFIG_SAMPLES)	+= markers/ kobject/ kprobes/ tracepoints/ trace_events/

# builds the trace events example kernel modules;

# then to use one (as root):  insmod <module_name.ko>

PWD := $(shell pwd)

CFLAGS_trace-events-sample.o := -I$(PWD)/samples/trace_events/

obj-$(CONFIG_SAMPLE_TRACE_EVENTS) += trace-events-sample.o

#include <linux/module.h>

#include <linux/kthread.h>

/*

 * Any file that uses trace points, must include the header.

 * But only one file, must include the header by defining

 * CREATE_TRACE_POINTS first.  This will make the C code that

 * creates the handles for the trace points.

 */

#define CREATE_TRACE_POINTS

#include "trace-events-sample.h"

static void simple_thread_func(int cnt)

{

	set_current_state(TASK_INTERRUPTIBLE);

	schedule_timeout(HZ);

	trace_foo_bar("hello", cnt);

	if (!(cnt % 10))

		/* It is really important that I say "hi!" */

		printk(KERN_EMERG "hi!\n");

}

static int simple_thread(void *arg)

{

	int cnt = 0;

	while (!kthread_should_stop())

		simple_thread_func(cnt++);

	return 0;

}

static struct task_struct *simple_tsk;

static int __init trace_event_init(void)

{

	simple_tsk = kthread_run(simple_thread, NULL, "event-sample");

	if (IS_ERR(simple_tsk))

		return -1;

	return 0;

}

static void __exit trace_event_exit(void)

{

	kthread_stop(simple_tsk);

}

module_init(trace_event_init);

module_exit(trace_event_exit);

MODULE_AUTHOR("Steven Rostedt");

MODULE_DESCRIPTION("trace-events-sample");

MODULE_LICENSE("GPL");

/*

 * Notice that this file is not protected like a normal header.

 * We also must allow for rereading of this file. The

 *

 *  || defined(TRACE_HEADER_MULTI_READ)

 *

 * serves this purpose.

 */

#if !defined(_TRACE_EVENT_SAMPLE_H) || defined(TRACE_HEADER_MULTI_READ)

#define _TRACE_EVENT_SAMPLE_H

/*

 * All trace headers should include tracepoint.h, until we finally

 * make it into a standard header.

 */

#include <linux/tracepoint.h>

/*

 * If TRACE_SYSTEM is defined, that will be the directory created

 * in the ftrace directory under /debugfs/tracing/events/<system>

 *

 * The define_trace.h belowe will also look for a file name of

 * TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here.

 *

 * If you want a different system than file name, you can override

 * the header name by defining TRACE_INCLUDE_FILE

 *

 * If this file was called, goofy.h, then we would define:

 *

 * #define TRACE_INCLUDE_FILE goofy

 *

 */

#undef TRACE_SYSTEM

#define TRACE_SYSTEM trace-events-sample

/*

 * The TRACE_EVENT macro is broken up into 5 parts.

 *

 * name: name of the trace point. This is also how to enable the tracepoint.

 *   A function called trace_foo_bar() will be created.

 *

 * proto: the prototype of the function trace_foo_bar()

 *   Here it is trace_foo_bar(char *foo, int bar).

 *

 * args:  must match the arguments in the prototype.

 *    Here it is simply "foo, bar".

 *

 * struct:  This defines the way the data will be stored in the ring buffer.

 *    There are currently two types of elements. __field and __array.

 *    a __field is broken up into (type, name). Where type can be any

 *    type but an array.

 *    For an array. there are three fields. (type, name, size). The

 *    type of elements in the array, the name of the field and the size

 *    of the array.

 *

 *    __array( char, foo, 10) is the same as saying   char foo[10].

 *

 * fast_assign: This is a C like function that is used to store the items

 *    into the ring buffer.

 *

 * printk: This is a way to print out the data in pretty print. This is

 *    useful if the system crashes and you are logging via a serial line,

 *    the data can be printed to the console using this "printk" method.

 *

 * Note, that for both the assign and the printk, __entry is the handler

 * to the data structure in the ring buffer, and is defined by the

 * TP_STRUCT__entry.

 */

TRACE_EVENT(foo_bar,

	TP_PROTO(char *foo, int bar),

	TP_ARGS(foo, bar),

	TP_STRUCT__entry(

		__array(	char,	foo,    10		)

		__field(	int,	bar			)

	),

	TP_fast_assign(

		strncpy(__entry->foo, foo, 10);

		__entry->bar	= bar;

	),

	TP_printk("foo %s %d", __entry->foo, __entry->bar)

);

#endif

/***** NOTICE! The #if protection ends here. *****/

/*

 * There are several ways I could have done this. If I left out the

 * TRACE_INCLUDE_PATH, then it would default to the kernel source

 * include/trace/events directory.

 *

 * I could specify a path from the define_trace.h file back to this

 * file.

 *

 * #define TRACE_INCLUDE_PATH ../../samples/trace_events

 *

 * But I chose to simply make it use the current directory and then in

 * the Makefile I added:

 *

 * CFLAGS_trace-events-sample.o := -I$(PWD)/samples/trace_events/

 *

 * This will make sure the current path is part of the include

 * structure for our file so that we can find it.

 *

 * I could have made only the top level directory the include:

 *

 * CFLAGS_trace-events-sample.o := -I$(PWD)

 *

 * And then let the path to this directory be the TRACE_INCLUDE_PATH:

 *

 * #define TRACE_INCLUDE_PATH samples/trace_events

 *

 * But then if something defines "samples" or "trace_events" then we

 * could risk that being converted too, and give us an unexpected

 * result.

 */

#undef TRACE_INCLUDE_PATH

#define TRACE_INCLUDE_PATH .

#include <trace/define_trace.h>