驅動程式 - Linux Device Driver(LDD) - 解決/sys/kernel/tracing/沒有內容的問題

參考資訊：
https://docs.kernel.org/trace/debugging.html

~ # ls /sys/kernel/tracing/

~ # mount -t tracefs tracefs /sys/kernel/tracing/

~ # ls /sys/kernel/tracing/
    README                      set_event
    available_events            set_event_notrace_pid
    available_filter_functions  set_event_pid
    available_tracers           set_ftrace_filter
    buffer_percent              set_ftrace_notrace
    buffer_size_kb              set_ftrace_notrace_pid
    buffer_total_size_kb        set_ftrace_pid
    current_tracer              set_graph_function
    dyn_ftrace_total_info       set_graph_notrace
    dynamic_events              snapshot
    enabled_functions           stack_max_size
    error_log                   stack_trace
    eval_map                    stack_trace_filter
    events                      synthetic_events
    free_buffer                 timestamp_mode
    function_profile_enabled    trace
    hwlat_detector              trace_clock
    instances                   trace_marker
    max_graph_depth             trace_marker_raw
    options                     trace_options
    osnoise                     trace_pipe
    per_cpu                     trace_stat
    printk_formats              tracing_cpumask
    recursed_functions          tracing_max_latency
    rv                          tracing_on
    saved_cmdlines              tracing_thresh
    saved_cmdlines_size         uprobe_events
    saved_tgids                 uprobe_profile