tracing: Add enabling of events to boot instances

Add the format of:

  trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall

That will create the "foo" instance and enable the sched_switch event
(here were the "sched" system is explicitly specified), the
irq_handler_entry event, and all events under the system initcall.

Link: https://lkml.kernel.org/r/20230207173026.386114535@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Ross Zwisler <zwisler@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -6278,6 +6278,20 @@
 
 				/sys/kernel/tracing/instances
 
+			Events can be enabled at the time the instance is created
+			via:
+
+				trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
+
+			Note, the "<system*>:" portion is optional if the event is
+			unique.
+
+				trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
+
+			will enable the "sched_switch" event (note, the "sched:" is optional, and
+			the same thing would happen if it was left off). The irq_handler_entry
+			event, and all events under the "initcall" system.
+
 	trace_options=[option-list]
 			[FTRACE] Enable or disable tracer options at boot.
 			The option-list is a comma delimited list of options

kernel/trace/trace.c

@@ -10188,6 +10188,10 @@ __init static void enable_instances(void)
 		}
 		/* Allow user space to delete it */
 		trace_array_put(tr);
+
+		while ((tok = strsep(&curr_str, ","))) {
+			early_enable_events(tr, tok, true);
+		}
 	}
 }
 

kernel/trace/trace.h

@@ -1334,6 +1334,8 @@ DECLARE_PER_CPU(int, trace_buffered_event_cnt);
 void trace_buffered_event_disable(void);
 void trace_buffered_event_enable(void);
 
+void early_enable_events(struct trace_array *tr, char *buf, bool disable_first);
+
 static inline void
 __trace_event_discard_commit(struct trace_buffer *buffer,
 			     struct ring_buffer_event *event)

kernel/trace/trace_events.c

@@ -3750,10 +3750,9 @@ static __init int event_trace_memsetup(void)
 	return 0;
 }
 
-static __init void
-early_enable_events(struct trace_array *tr, bool disable_first)
+__init void
+early_enable_events(struct trace_array *tr, char *buf, bool disable_first)
 {
-	char *buf = bootup_event_buf;
 	char *token;
 	int ret;
 
@@ -3806,7 +3805,7 @@ static __init int event_trace_enable(void)
 	 */
 	__trace_early_add_events(tr);
 
-	early_enable_events(tr, false);
+	early_enable_events(tr, bootup_event_buf, false);
 
 	trace_printk_start_comm();
 
@@ -3834,7 +3833,7 @@ static __init int event_trace_enable_again(void)
 	if (!tr)
 		return -ENODEV;
 
-	early_enable_events(tr, true);
+	early_enable_events(tr, bootup_event_buf, true);
 
 	return 0;
 }