1// SPDX-License-Identifier: GPL-2.0-only
  2#include <linux/module.h>
  3#include <linux/kthread.h>
  4#include <linux/trace.h>
  5#include <linux/trace_events.h>
  6#include <linux/timer.h>
  7#include <linux/err.h>
  8#include <linux/jiffies.h>
  9#include <linux/workqueue.h>
 10
 11/*
 12 * Any file that uses trace points, must include the header.
 13 * But only one file, must include the header by defining
 14 * CREATE_TRACE_POINTS first.  This will make the C code that
 15 * creates the handles for the trace points.
 16 */
 17#define CREATE_TRACE_POINTS
 18#include "sample-trace-array.h"
 19
 20struct trace_array *tr;
 21static void mytimer_handler(struct timer_list *unused);
 22static struct task_struct *simple_tsk;
 23
 24static void trace_work_fn(struct work_struct *work)
 25{
 26	/*
 27	 * Disable tracing for event "sample_event".
 28	 */
 29	trace_array_set_clr_event(tr, "sample-subsystem", "sample_event",
 30			false);
 31}
 32static DECLARE_WORK(trace_work, trace_work_fn);
 33
 34/*
 35 * mytimer: Timer setup to disable tracing for event "sample_event". This
 36 * timer is only for the purposes of the sample module to demonstrate access of
 37 * Ftrace instances from within kernel.
 38 */
 39static DEFINE_TIMER(mytimer, mytimer_handler);
 40
 41static void mytimer_handler(struct timer_list *unused)
 42{
 43	schedule_work(&trace_work);
 44}
 45
 46static void simple_thread_func(int count)
 47{
 48	set_current_state(TASK_INTERRUPTIBLE);
 49	schedule_timeout(HZ);
 50
 51	/*
 52	 * Printing count value using trace_array_printk() - trace_printk()
 53	 * equivalent for the instance buffers.
 54	 */
 55	trace_array_printk(tr, _THIS_IP_, "trace_array_printk: count=%d\n",
 56			count);
 57	/*
 58	 * Tracepoint for event "sample_event". This will print the
 59	 * current value of count and current jiffies.
 60	 */
 61	trace_sample_event(count, jiffies);
 62}
 63
 64static int simple_thread(void *arg)
 65{
 66	int count = 0;
 67	unsigned long delay = msecs_to_jiffies(5000);
 68
 69	/*
 70	 * Enable tracing for "sample_event".
 71	 */
 72	trace_array_set_clr_event(tr, "sample-subsystem", "sample_event", true);
 73
 74	/*
 75	 * Adding timer - mytimer. This timer will disable tracing after
 76	 * delay seconds.
 77	 *
 78	 */
 79	add_timer(&mytimer);
 80	mod_timer(&mytimer, jiffies+delay);
 81
 82	while (!kthread_should_stop())
 83		simple_thread_func(count++);
 84
 85	del_timer(&mytimer);
 86	cancel_work_sync(&trace_work);
 87
 88	/*
 89	 * trace_array_put() decrements the reference counter associated with
 90	 * the trace array - "tr". We are done using the trace array, hence
 91	 * decrement the reference counter so that it can be destroyed using
 92	 * trace_array_destroy().
 93	 */
 94	trace_array_put(tr);
 95
 96	return 0;
 97}
 98
 99static int __init sample_trace_array_init(void)
100{
101	/*
102	 * Return a pointer to the trace array with name "sample-instance" if it
103	 * exists, else create a new trace array.
104	 *
105	 * NOTE: This function increments the reference counter
106	 * associated with the trace array - "tr".
107	 */
108	tr = trace_array_get_by_name("sample-instance", "sched,timer,kprobes");
109
110	if (!tr)
111		return -1;
112	/*
113	 * If context specific per-cpu buffers havent already been allocated.
114	 */
115	trace_printk_init_buffers();
116
117	simple_tsk = kthread_run(simple_thread, NULL, "sample-instance");
118	if (IS_ERR(simple_tsk)) {
119		trace_array_put(tr);
120		trace_array_destroy(tr);
121		return -1;
122	}
123
124	return 0;
125}
126
127static void __exit sample_trace_array_exit(void)
128{
129	kthread_stop(simple_tsk);
130
131	/*
132	 * We are unloading our module and no longer require the trace array.
133	 * Remove/destroy "tr" using trace_array_destroy()
134	 */
135	trace_array_destroy(tr);
136}
137
138module_init(sample_trace_array_init);
139module_exit(sample_trace_array_exit);
140
141MODULE_AUTHOR("Divya Indi");
142MODULE_DESCRIPTION("Sample module for kernel access to Ftrace instances");
143MODULE_LICENSE("GPL");