tracing: Add trigger file for trace_markers tracefs/ftrace/print

Allow writing to the trace_markers file initiate triggers defined in
tracefs/ftrace/print/trigger file. This will allow of user space to trigger
the same type of triggers (including histograms) that the trace events use.

Had to create a ftrace_event_register() function that will become the
trace_marker print event's reg() function. This is required because of how
triggers are enabled:

  event_trigger_write() {
    event_trigger_regex_write() {
      trigger_process_regex() {
        for p in trigger_commands {
          p->func(); /* trigger_snapshot_cmd->func */
            event_trigger_callback() {
              cmd_ops->reg() /* register_trigger() */ {
                trace_event_trigger_enable_disable() {
                  trace_event_enable_disable() {
                    call->class->reg();

Without the reg() function, the trigger code will call a NULL pointer and
crash the system.

Cc: Tom Zanussi <[email protected]>
Cc: Clark Williams <[email protected]>
Cc: Karim Yaghmour <[email protected]>
Cc: Brendan Gregg <[email protected]>
Suggested-by: Joel Fernandes <[email protected]>
Reviewed-by: Namhyung Kim <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

0 files changed, 0 insertions, 0 deletions