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![Divya Indi](/assets/img/avatar_default.png)
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>
131 lines
3.3 KiB
C
131 lines
3.3 KiB
C
// 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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