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