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>

1 files changed, 14 insertions, 0 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9545da5ed849..40304dc3d319 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/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