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
  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
  19 struct trace_array *tr;
  20 static void mytimer_handler(struct timer_list *unused);
  21 static 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  */
  28 static DEFINE_TIMER(mytimer, mytimer_handler);
  29
  30 static 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
  39 static 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
  57 static 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
  91 static 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
 115 static 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
 126 module_init(sample_trace_array_init);
 127 module_exit(sample_trace_array_exit);
 128
 129 MODULE_AUTHOR("Divya Indi");
 130 MODULE_DESCRIPTION("Sample module for kernel access to Ftrace instances");
 131 MODULE_LICENSE("GPL");