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