Commit 9cfe06f8 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt

tracing/events: add trace-events-sample

This patch adds a sample to the samples directory on how to create
and use TRACE_EVENT trace points.
Signed-off-by: default avatarSteven Rostedt <>
parent ad8d75ff
......@@ -19,6 +19,13 @@ config SAMPLE_TRACEPOINTS
This build tracepoints example modules.
tristate "Build trace_events examples"
depends on EVENT_TRACING
default m
This build trace event example modules.
tristate "Build kobject examples"
# 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.
#include "trace-events-sample.h"
static void simple_thread_func(int cnt)
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())
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)
MODULE_AUTHOR("Steven Rostedt");
* Notice that this file is not protected like a normal header.
* We also must allow for rereading of this file. The
* serves this purpose.
* 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
#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.
TP_PROTO(char *foo, int bar),
TP_ARGS(foo, bar),
__array( char, foo, 10 )
__field( int, bar )
strncpy(__entry->foo, foo, 10);
__entry->bar = bar;
TP_printk("foo %s %d", __entry->foo, __entry->bar)
/***** 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.
#include <trace/define_trace.h>
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