tracing: Always show all tracer options in the options directory

There are options that are unique to a specific tracer (like function and
function graph). Currently, these options are only visible in the options
directory when the tracer is enabled.

This has been a pain, especially for something like the func_stack_trace
option that if used inappropriately, could bring the system to a crawl. But
the only way to see it, is to enable the function tracer.

For example, if one had done:

 # cd /sys/kernel/tracing
 # echo __schedule > set_ftrace_filter
 # echo 1 > options/func_stack_trace
 # echo function > current_tracer

The __schedule call will be traced and a stack trace will also be recorded
there. Now when you were done, you may do...

 # echo nop > current_tracer
 # echo > set_ftrace_filter

But you forgot to disable the func_stack_trace. The only way to disable it
is to re-enable function tracing first. If you do not add a filter to
set_ftrace_filter and just do:

 # echo function > current_tracer

Now you would be performing a stack trace on *every* function! On some
systems, that causes a live lock. Others may take a few minutes to fix your
mistake.

Having the func_stack_trace option visible allows you to check it and
disable it before enabling the funtion tracer.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index af34e1822dad..8ed97872b65b 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -333,6 +333,13 @@ struct tracer_flags {
 #define TRACER_OPT(s, b)	.name = #s, .bit = b
 
 
+struct trace_option_dentry {
+	struct tracer_opt		*opt;
+	struct tracer_flags		*flags;
+	struct trace_array		*tr;
+	struct dentry			*entry;
+};
+
 /**
  * struct tracer - a specific tracer and its callbacks to interact with tracefs
  * @name: the name chosen to select it on the available_tracers file
@@ -387,6 +394,7 @@ struct tracer {
 						u32 mask, int set);
 	struct tracer		*next;
 	struct tracer_flags	*flags;
+	struct trace_option_dentry *topts;
 	int			enabled;
 	int			ref;
 	bool			print_max;