• Divya Indi's avatar
    tracing: Sample module to demonstrate kernel access to Ftrace instances. · 89ed4249
    Divya Indi authored
    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.comReviewed-by: default avatarAruna Ramakrishna <aruna.ramakrishna@oracle.com>
    Signed-off-by: default avatarDivya Indi <divya.indi@oracle.com>
    [ Moved to samples/ftrace ]
    Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    89ed4249
sample-trace-array.h 2.37 KB