// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/trace.h>
#include <linux/trace_events.h>
#include <linux/timer.h>
#include <linux/err.h>
#include <linux/jiffies.h>
#include <linux/workqueue.h>

/*
 * Any file that uses trace points, must include the header.
 * But only one file, must include the header by defining
 * CREATE_TRACE_POINTS first.  This will make the C code that
 * creates the handles for the trace points.
 */
#define CREATE_TRACE_POINTS
#include "sample-trace-array.h"

struct trace_array *tr;
static void mytimer_handler(struct timer_list *unused);
static struct task_struct *simple_tsk;

static void trace_work_fn(struct work_struct *work)
{
        /*
         * Disable tracing for event "sample_event".
         */
        trace_array_set_clr_event(tr, "sample-subsystem", "sample_event",
                        false);
}
static DECLARE_WORK(trace_work, trace_work_fn);

/*
 * mytimer: Timer setup to disable tracing for event "sample_event". This
 * timer is only for the purposes of the sample module to demonstrate access of
 * Ftrace instances from within kernel.
 */
static DEFINE_TIMER(mytimer, mytimer_handler);

static void mytimer_handler(struct timer_list *unused)
{
        schedule_work(&trace_work);
}

static void simple_thread_func(int count)
{
        set_current_state(TASK_INTERRUPTIBLE);
        schedule_timeout(HZ);

        /*
         * Printing count value using trace_array_printk() - trace_printk()
         * equivalent for the instance buffers.
         */
        trace_array_printk(tr, _THIS_IP_, "trace_array_printk: count=%d\n",
                        count);
        /*
         * Tracepoint for event "sample_event". This will print the
         * current value of count and current jiffies.
         */
        trace_sample_event(count, jiffies);
}

static int simple_thread(void *arg)
{
        int count = 0;
        unsigned long delay = msecs_to_jiffies(5000);

        /*
         * Enable tracing for "sample_event".
         */
        trace_array_set_clr_event(tr, "sample-subsystem", "sample_event", true);

        /*
         * Adding timer - mytimer. This timer will disable tracing after
         * delay seconds.
         *
         */
        add_timer(&mytimer);
        mod_timer(&mytimer, jiffies+delay);

        while (!kthread_should_stop())
                simple_thread_func(count++);

        timer_delete(&mytimer);
        cancel_work_sync(&trace_work);

        /*
         * trace_array_put() decrements the reference counter associated with
         * the trace array - "tr". We are done using the trace array, hence
         * decrement the reference counter so that it can be destroyed using
         * trace_array_destroy().
         */
        trace_array_put(tr);

        return 0;
}

static int __init sample_trace_array_init(void)
{
        /*
         * Return a pointer to the trace array with name "sample-instance" if it
         * exists, else create a new trace array.
         *
         * NOTE: This function increments the reference counter
         * associated with the trace array - "tr".
         */
        tr = trace_array_get_by_name("sample-instance", "sched,timer,kprobes");

        if (!tr)
                return -1;
        /*
         * If context specific per-cpu buffers havent already been allocated.
         */
        trace_array_init_printk(tr);

        simple_tsk = kthread_run(simple_thread, NULL, "sample-instance");
        if (IS_ERR(simple_tsk)) {
                trace_array_put(tr);
                trace_array_destroy(tr);
                return -1;
        }

        return 0;
}

static void __exit sample_trace_array_exit(void)
{
        kthread_stop(simple_tsk);

        /*
         * We are unloading our module and no longer require the trace array.
         * Remove/destroy "tr" using trace_array_destroy()
         */
        trace_array_destroy(tr);
}

module_init(sample_trace_array_init);
module_exit(sample_trace_array_exit);

MODULE_AUTHOR("Divya Indi");
MODULE_DESCRIPTION("Sample module for kernel access to Ftrace instances");
MODULE_LICENSE("GPL");