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 <tom.zanussi@linux.intel.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Karim Yaghmour <karim.yaghmour@opersys.com>
Cc: Brendan Gregg <bgregg@netflix.com>
Suggested-by: Joel Fernandes <joelaf@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index e3a658bac10f..1d67464ed95e 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -230,7 +230,7 @@ FTRACE_ENTRY(bprint, bprint_entry,
 	FILTER_OTHER
 );
 
-FTRACE_ENTRY(print, print_entry,
+FTRACE_ENTRY_REG(print, print_entry,
 
 	TRACE_PRINT,
 
@@ -242,7 +242,9 @@ FTRACE_ENTRY(print, print_entry,
 	F_printk("%ps: %s",
 		 (void *)__entry->ip, __entry->buf),
 
-	FILTER_OTHER
+	FILTER_OTHER,
+
+	ftrace_event_register
 );
 
 FTRACE_ENTRY(raw_data, raw_data_entry,