Re: [PATCH 4/4] tracing/events: add trace-events-sample

Frederic Weisbecker
2009-04-15T16:15:41Z

On Tue, Apr 14, 2009 at 11:15:15PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
>
> This patch adds a sample to the samples directory on how to create
> and use TRACE_EVENT trace points.
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> samples/Kconfig | 7 ++
> samples/Makefile | 2 +-
> samples/trace_events/Makefile | 8 ++
> samples/trace_events/trace-events-sample.c | 56 +++++++++++++
> samples/trace_events/trace-events-sample.h | 124 ++++++++++++++++++++++++++++
> 5 files changed, 196 insertions(+), 1 deletions(-)
> create mode 100644 samples/trace_events/Makefile
> create mode 100644 samples/trace_events/trace-events-sample.c
> create mode 100644 samples/trace_events/trace-events-sample.h
>
> diff --git a/samples/Kconfig b/samples/Kconfig
> index 4b02f5a..93f41c0 100644
> --- a/samples/Kconfig
> +++ b/samples/Kconfig
> @@ -19,6 +19,13 @@ config SAMPLE_TRACEPOINTS
> 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
> diff --git a/samples/Makefile b/samples/Makefile
> index 10eaca8..13e4b47 100644
> --- a/samples/Makefile
> +++ b/samples/Makefile
> @@ -1,3 +1,3 @@
> # Makefile for Linux samples code
>
> -obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/
> +obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/ trace_events/
> diff --git a/samples/trace_events/Makefile b/samples/trace_events/Makefile
> new file mode 100644
> index 0000000..06c6dea
> --- /dev/null
> +++ b/samples/trace_events/Makefile
> @@ -0,0 +1,8 @@
> +# 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
> diff --git a/samples/trace_events/trace-events-sample.c b/samples/trace_events/trace-events-sample.c
> new file mode 100644
> index 0000000..f33b3ba
> --- /dev/null
> +++ b/samples/trace_events/trace-events-sample.c
> @@ -0,0 +1,56 @@
> +#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!" */

Nice design choice! Indeed this is very important! ;-)

Frederic.

> + 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");
> diff --git a/samples/trace_events/trace-events-sample.h b/samples/trace_events/trace-events-sample.h
> new file mode 100644
> index 0000000..eab4644
> --- /dev/null
> +++ b/samples/trace_events/trace-events-sample.h
> @@ -0,0 +1,124 @@
> +/*
> + * 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>
> --
> 1.6.2.1
>
> --