samples/ftrace/sample-trace-array.c

   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
  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
  41 static void mytimer_handler(struct timer_list *unused)
  42 {
  43         schedule_work(&trace_work);
  44 }
  45
  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
  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
  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", "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
 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");