144 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2#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 defining14 * CREATE_TRACE_POINTS first. This will make the C code that15 * creates the handles for the trace points.16 */17#define CREATE_TRACE_POINTS18#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". This36 * timer is only for the purposes of the sample module to demonstrate access of37 * 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 the59 * 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 after76 * 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 with90 * the trace array - "tr". We are done using the trace array, hence91 * decrement the reference counter so that it can be destroyed using92 * 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 it103 * exists, else create a new trace array.104 *105 * NOTE: This function increments the reference counter106 * 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");144