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 
20 struct trace_array *tr;
21 static void mytimer_handler(struct timer_list *unused);
22 static struct task_struct *simple_tsk;
23 
trace_work_fn(struct work_struct * work)24 static 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 }
32 static 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  */
39 static DEFINE_TIMER(mytimer, mytimer_handler);
40 
mytimer_handler(struct timer_list * unused)41 static void mytimer_handler(struct timer_list *unused)
42 {
43 	schedule_work(&trace_work);
44 }
45 
simple_thread_func(int count)46 static 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 
simple_thread(void * arg)64 static 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 
sample_trace_array_init(void)99 static 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");
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 
sample_trace_array_exit(void)127 static 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 
138 module_init(sample_trace_array_init);
139 module_exit(sample_trace_array_exit);
140 
141 MODULE_AUTHOR("Divya Indi");
142 MODULE_DESCRIPTION("Sample module for kernel access to Ftrace instances");
143 MODULE_LICENSE("GPL");
144