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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
..
auxdisplay auxdisplay: Fix a typo in cfag12864b-example.c 2019-08-08 20:00:18 +02:00
binderfs treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
bpf samples/bpf: Add a workaround for asm_inline 2019-10-03 17:37:11 +02:00
configfs treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 145 2019-05-30 11:25:18 -07:00
connector treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
ftrace tracing: Sample module to demonstrate kernel access to Ftrace instances. 2019-11-22 19:41:08 -05:00
hidraw
hw_breakpoint treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
kdb treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
kfifo treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 465 2019-06-19 17:09:10 +02:00
kobject treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
kprobes treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
livepatch treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
mei samples: mei: use /dev/mei0 instead of /dev/mei 2019-01-30 15:24:45 +01:00
mic/mpssd treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 290 2019-06-05 17:36:38 +02:00
pidfd samples: make pidfd-metadata fail gracefully on older kernels 2019-06-24 15:55:50 +02:00
pktgen samples: pktgen: allow to specify destination port 2019-07-01 11:02:20 -07:00
qmi treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
rpmsg samples/rpmsg: Introduce a module parameter for message count 2019-08-26 22:10:39 -07:00
seccomp samples: guard sub-directories with CONFIG options 2019-05-18 11:29:01 +09:00
timers
trace_events sched/core: Provide a pointer to the valid CPU mask 2019-06-03 11:49:37 +02:00
trace_printk treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
uhid treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
v4l media: v4l2-pci-skeleton.c: fix doc warning 2019-05-28 13:14:28 -04:00
vfio-mdev vfio-mdev/mtty: Simplify interrupt generation 2019-08-19 13:28:57 -06:00
vfs treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
watchdog
Kconfig tracing: Sample module to demonstrate kernel access to Ftrace instances. 2019-11-22 19:41:08 -05:00
Makefile tracing: Sample module to demonstrate kernel access to Ftrace instances. 2019-11-22 19:41:08 -05:00