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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>
This commit is contained in:
Divya Indi
Steven Rostedt (VMware)
parent
2887978714
commit
89ed42495e
@ -27,6 +27,13 @@ config SAMPLE_FTRACE_DIRECT
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This builds an ftrace direct function example
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that hooks to wake_up_process and prints the parameters.
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config SAMPLE_TRACE_ARRAY
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tristate "Build sample module for kernel access to Ftrace instancess"
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depends on EVENT_TRACING && m
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help
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This builds a module that demonstrates the use of various APIs to
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access Ftrace instances from within the kernel.
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config SAMPLE_KOBJECT
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tristate "Build kobject examples"
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help
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@ -18,6 +18,7 @@ subdir-$(CONFIG_SAMPLE_SECCOMP) += seccomp
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obj-$(CONFIG_SAMPLE_TRACE_EVENTS) += trace_events/
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obj-$(CONFIG_SAMPLE_TRACE_PRINTK) += trace_printk/
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace/
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obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += ftrace/
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obj-$(CONFIG_VIDEO_PCI_SKELETON) += v4l/
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obj-y += vfio-mdev/
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subdir-$(CONFIG_SAMPLE_VFS) += vfs
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@ -3,3 +3,6 @@
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct.o
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-too.o
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obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-modify.o
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CFLAGS_sample-trace-array.o := -I$(src)
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obj-$(CONFIG_SAMPLE_TRACE_ARRAY) += sample-trace-array.o
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131
samples/ftrace/sample-trace-array.c
Normal file
131
samples/ftrace/sample-trace-array.c
Normal file
@ -0,0 +1,131 @@
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// SPDX-License-Identifier: GPL-2.0-only
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#include <linux/module.h>
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#include <linux/kthread.h>
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#include <linux/trace.h>
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#include <linux/trace_events.h>
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#include <linux/timer.h>
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#include <linux/err.h>
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#include <linux/jiffies.h>
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/*
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* Any file that uses trace points, must include the header.
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* But only one file, must include the header by defining
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* CREATE_TRACE_POINTS first. This will make the C code that
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* creates the handles for the trace points.
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*/
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#define CREATE_TRACE_POINTS
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#include "sample-trace-array.h"
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struct trace_array *tr;
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static void mytimer_handler(struct timer_list *unused);
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static struct task_struct *simple_tsk;
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/*
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* mytimer: Timer setup to disable tracing for event "sample_event". This
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* timer is only for the purposes of the sample module to demonstrate access of
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* Ftrace instances from within kernel.
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*/
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static DEFINE_TIMER(mytimer, mytimer_handler);
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static void mytimer_handler(struct timer_list *unused)
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{
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/*
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* Disable tracing for event "sample_event".
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*/
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trace_array_set_clr_event(tr, "sample-subsystem", "sample_event",
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false);
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}
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static void simple_thread_func(int count)
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{
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set_current_state(TASK_INTERRUPTIBLE);
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schedule_timeout(HZ);
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/*
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* Printing count value using trace_array_printk() - trace_printk()
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* equivalent for the instance buffers.
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*/
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trace_array_printk(tr, _THIS_IP_, "trace_array_printk: count=%d\n",
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count);
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/*
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* Tracepoint for event "sample_event". This will print the
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* current value of count and current jiffies.
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*/
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trace_sample_event(count, jiffies);
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}
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static int simple_thread(void *arg)
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{
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int count = 0;
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unsigned long delay = msecs_to_jiffies(5000);
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/*
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* Enable tracing for "sample_event".
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*/
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trace_array_set_clr_event(tr, "sample-subsystem", "sample_event", true);
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/*
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* Adding timer - mytimer. This timer will disable tracing after
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* delay seconds.
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*
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*/
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add_timer(&mytimer);
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mod_timer(&mytimer, jiffies+delay);
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while (!kthread_should_stop())
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simple_thread_func(count++);
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del_timer(&mytimer);
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/*
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* trace_array_put() decrements the reference counter associated with
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* the trace array - "tr". We are done using the trace array, hence
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* decrement the reference counter so that it can be destroyed using
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* trace_array_destroy().
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*/
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trace_array_put(tr);
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return 0;
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}
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static int __init sample_trace_array_init(void)
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{
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/*
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* Return a pointer to the trace array with name "sample-instance" if it
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* exists, else create a new trace array.
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*
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* NOTE: This function increments the reference counter
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* associated with the trace array - "tr".
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*/
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tr = trace_array_get_by_name("sample-instance");
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if (!tr)
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return -1;
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/*
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* If context specific per-cpu buffers havent already been allocated.
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*/
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trace_printk_init_buffers();
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simple_tsk = kthread_run(simple_thread, NULL, "sample-instance");
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if (IS_ERR(simple_tsk))
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return -1;
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return 0;
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}
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static void __exit sample_trace_array_exit(void)
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{
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kthread_stop(simple_tsk);
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/*
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* We are unloading our module and no longer require the trace array.
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* Remove/destroy "tr" using trace_array_destroy()
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*/
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trace_array_destroy(tr);
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}
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module_init(sample_trace_array_init);
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module_exit(sample_trace_array_exit);
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MODULE_AUTHOR("Divya Indi");
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MODULE_DESCRIPTION("Sample module for kernel access to Ftrace instances");
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MODULE_LICENSE("GPL");
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84
samples/ftrace/sample-trace-array.h
Normal file
84
samples/ftrace/sample-trace-array.h
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@ -0,0 +1,84 @@
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/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* If TRACE_SYSTEM is defined, that will be the directory created
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* in the ftrace directory under /sys/kernel/tracing/events/<system>
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*
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* The define_trace.h below will also look for a file name of
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* TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here.
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* In this case, it would look for sample-trace.h
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*
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* If the header name will be different than the system name
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* (as in this case), then you can override the header name that
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* define_trace.h will look up by defining TRACE_INCLUDE_FILE
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*
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* This file is called sample-trace-array.h but we want the system
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* to be called "sample-subsystem". Therefore we must define the name of this
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* file:
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*
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* #define TRACE_INCLUDE_FILE sample-trace-array
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*
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* As we do in the bottom of this file.
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*
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* Notice that TRACE_SYSTEM should be defined outside of #if
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* protection, just like TRACE_INCLUDE_FILE.
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*/
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#undef TRACE_SYSTEM
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#define TRACE_SYSTEM sample-subsystem
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/*
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* TRACE_SYSTEM is expected to be a C valid variable (alpha-numeric
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* and underscore), although it may start with numbers. If for some
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* reason it is not, you need to add the following lines:
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*/
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#undef TRACE_SYSTEM_VAR
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#define TRACE_SYSTEM_VAR sample_subsystem
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/*
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* But the above is only needed if TRACE_SYSTEM is not alpha-numeric
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* and underscored. By default, TRACE_SYSTEM_VAR will be equal to
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* TRACE_SYSTEM. As TRACE_SYSTEM_VAR must be alpha-numeric, if
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* TRACE_SYSTEM is not, then TRACE_SYSTEM_VAR must be defined with
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* only alpha-numeric and underscores.
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*
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* The TRACE_SYSTEM_VAR is only used internally and not visible to
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* user space.
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*/
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/*
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* Notice that this file is not protected like a normal header.
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* We also must allow for rereading of this file. The
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*
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* || defined(TRACE_HEADER_MULTI_READ)
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*
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* serves this purpose.
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*/
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#if !defined(_SAMPLE_TRACE_ARRAY_H) || defined(TRACE_HEADER_MULTI_READ)
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#define _SAMPLE_TRACE_ARRAY_H
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#include <linux/tracepoint.h>
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TRACE_EVENT(sample_event,
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TP_PROTO(int count, unsigned long time),
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TP_ARGS(count, time),
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TP_STRUCT__entry(
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__field(int, count)
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__field(unsigned long, time)
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),
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TP_fast_assign(
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__entry->count = count;
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__entry->time = time;
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),
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TP_printk("count value=%d at jiffies=%lu", __entry->count,
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__entry->time)
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);
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#endif
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#undef TRACE_INCLUDE_PATH
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#define TRACE_INCLUDE_PATH .
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#define TRACE_INCLUDE_FILE sample-trace-array
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#include <trace/define_trace.h>
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