linux/samples/ftrace/sample-trace-array.c
Divya Indi 89ed42495e tracing: Sample module to demonstrate kernel access to Ftrace instances.
This is a sample module to demonstrate the use of the newly introduced and
exported APIs to access Ftrace instances from within the kernel.

Newly introduced APIs used here -

1. Create/Lookup a trace array with the given name.
struct trace_array *trace_array_get_by_name(const char *name)

2. Destroy/Remove a trace array.
int trace_array_destroy(struct trace_array *tr)

4. Enable/Disable trace events:
int trace_array_set_clr_event(struct trace_array *tr, const char *system,
        const char *event, bool enable);

Exported APIs -
1. trace_printk equivalent for instances.
int trace_array_printk(struct trace_array *tr,
               unsigned long ip, const char *fmt, ...);

2. Helper function.
void trace_printk_init_buffers(void);

3. To decrement the reference counter.
void trace_array_put(struct trace_array *tr)

Sample output(contents of /sys/kernel/tracing/instances/sample-instance)
NOTE: Tracing disabled after ~5 sec)

                              _-----=> irqs-off
                             / _----=> need-resched
                            | / _---=> hardirq/softirq
                            || / _--=> preempt-depth
                            ||| /     delay
           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
              | |       |   ||||       |         |
sample-instance-1452  [002] ....    49.430948: simple_thread: trace_array_printk: count=0
sample-instance-1452  [002] ....    49.430951: sample_event: count value=0 at jiffies=4294716608
sample-instance-1452  [002] ....    50.454847: simple_thread: trace_array_printk: count=1
sample-instance-1452  [002] ....    50.454849: sample_event: count value=1 at jiffies=4294717632
sample-instance-1452  [002] ....    51.478748: simple_thread: trace_array_printk: count=2
sample-instance-1452  [002] ....    51.478750: sample_event: count value=2 at jiffies=4294718656
sample-instance-1452  [002] ....    52.502652: simple_thread: trace_array_printk: count=3
sample-instance-1452  [002] ....    52.502655: sample_event: count value=3 at jiffies=4294719680
sample-instance-1452  [002] ....    53.526533: simple_thread: trace_array_printk: count=4
sample-instance-1452  [002] ....    53.526535: sample_event: count value=4 at jiffies=4294720704
sample-instance-1452  [002] ....    54.550438: simple_thread: trace_array_printk: count=5
sample-instance-1452  [002] ....    55.574336: simple_thread: trace_array_printk: count=6

Link: http://lkml.kernel.org/r/1574276919-11119-3-git-send-email-divya.indi@oracle.com

Reviewed-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Signed-off-by: Divya Indi <divya.indi@oracle.com>
[ Moved to samples/ftrace ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2019-11-22 19:41:08 -05:00

132 lines
3.3 KiB
C

// 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");