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-rw-r--r--samples/ftrace/sample-trace-array.c131
1 files changed, 131 insertions, 0 deletions
diff --git a/samples/ftrace/sample-trace-array.c b/samples/ftrace/sample-trace-array.c
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+// 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>
+
+/*
+ * 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;
+
+/*
+ * 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)
+{
+ /*
+ * Disable tracing for event "sample_event".
+ */
+ trace_array_set_clr_event(tr, "sample-subsystem", "sample_event",
+ false);
+}
+
+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++);
+
+ del_timer(&mytimer);
+
+ /*
+ * 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");
+
+ if (!tr)
+ return -1;
+ /*
+ * If context specific per-cpu buffers havent already been allocated.
+ */
+ trace_printk_init_buffers();
+
+ simple_tsk = kthread_run(simple_thread, NULL, "sample-instance");
+ if (IS_ERR(simple_tsk))
+ 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");