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tracing: Sample module to demonstrate kernel access to Ftrace instances.

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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>
This commit is contained in:
Divya Indi 2019-11-20 11:08:39 -08:00 committed by Steven Rostedt (VMware)
parent 2887978714
commit 89ed42495e
5 changed files with 226 additions and 0 deletions
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7
samples/Kconfig
View File

@ -27,6 +27,13 @@ config SAMPLE_FTRACE_DIRECT
This builds an ftrace direct function example
that hooks to wake_up_process and prints the parameters.
config SAMPLE_TRACE_ARRAY
tristate "Build sample module for kernel access to Ftrace instancess"
depends on EVENT_TRACING && m
help
This builds a module that demonstrates the use of various APIs to
access Ftrace instances from within the kernel.
config SAMPLE_KOBJECT
tristate "Build kobject examples"
help

1
samples/Makefile
View File

@ -18,6 +18,7 @@ subdir-$(CONFIG_SAMPLE_SECCOMP) += seccomp
obj-$(CONFIG_SAMPLE_TRACE_EVENTS) += trace_events/
obj-$(CONFIG_SAMPLE_TRACE_PRINTK) += trace_printk/
obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace/
obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += ftrace/
obj-$(CONFIG_VIDEO_PCI_SKELETON) += v4l/
obj-y += vfio-mdev/
subdir-$(CONFIG_SAMPLE_VFS) += vfs

3
samples/ftrace/Makefile
View File

@ -3,3 +3,6 @@
obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct.o
obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-too.o
obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-modify.o
CFLAGS_sample-trace-array.o := -I$(src)
obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += sample-trace-array.o

131
samples/ftrace/sample-trace-array.c Normal file
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@ -0,0 +1,131 @@
// 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");

84
samples/ftrace/sample-trace-array.h Normal file
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@ -0,0 +1,84 @@
/* SPDX-License-Identifier: GPL-2.0 */
/*
* If TRACE_SYSTEM is defined, that will be the directory created
* in the ftrace directory under /sys/kernel/tracing/events/<system>
*
* The define_trace.h below will also look for a file name of
* TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here.
* In this case, it would look for sample-trace.h
*
* If the header name will be different than the system name
* (as in this case), then you can override the header name that
* define_trace.h will look up by defining TRACE_INCLUDE_FILE
*
* This file is called sample-trace-array.h but we want the system
* to be called "sample-subsystem". Therefore we must define the name of this
* file:
*
* #define TRACE_INCLUDE_FILE sample-trace-array
*
* As we do in the bottom of this file.
*
* Notice that TRACE_SYSTEM should be defined outside of #if
* protection, just like TRACE_INCLUDE_FILE.
*/
#undef TRACE_SYSTEM
#define TRACE_SYSTEM sample-subsystem
/*
* TRACE_SYSTEM is expected to be a C valid variable (alpha-numeric
* and underscore), although it may start with numbers. If for some
* reason it is not, you need to add the following lines:
*/
#undef TRACE_SYSTEM_VAR
#define TRACE_SYSTEM_VAR sample_subsystem
/*
* But the above is only needed if TRACE_SYSTEM is not alpha-numeric
* and underscored. By default, TRACE_SYSTEM_VAR will be equal to
* TRACE_SYSTEM. As TRACE_SYSTEM_VAR must be alpha-numeric, if
* TRACE_SYSTEM is not, then TRACE_SYSTEM_VAR must be defined with
* only alpha-numeric and underscores.
*
* The TRACE_SYSTEM_VAR is only used internally and not visible to
* user space.
*/
/*
* Notice that this file is not protected like a normal header.
* We also must allow for rereading of this file. The
*
* || defined(TRACE_HEADER_MULTI_READ)
*
* serves this purpose.
*/
#if !defined(_SAMPLE_TRACE_ARRAY_H) || defined(TRACE_HEADER_MULTI_READ)
#define _SAMPLE_TRACE_ARRAY_H
#include <linux/tracepoint.h>
TRACE_EVENT(sample_event,
TP_PROTO(int count, unsigned long time),
TP_ARGS(count, time),
TP_STRUCT__entry(
__field(int, count)
__field(unsigned long, time)
),
TP_fast_assign(
__entry->count = count;
__entry->time = time;
),
TP_printk("count value=%d at jiffies=%lu", __entry->count,
__entry->time)
);
#endif
#undef TRACE_INCLUDE_PATH
#define TRACE_INCLUDE_PATH .
#define TRACE_INCLUDE_FILE sample-trace-array
#include <trace/define_trace.h>