linux-kernel - [PATCH] ftrace: Document ftrace command line limitations

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Date:	Mon,  3 Nov 2014 20:45:25 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH] ftrace: Document ftrace command line limitations

When using the function or function_graph tracers from the command
line, certain command line options have limitations.

Document that only kernel built-in functions can be filtered via
ftrace_filter= or ftrace_graph_filter=. Also document that tracer-
specific options cannot be set on the command line via trace_options.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 Documentation/kernel-parameters.txt | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4c81a86..6f9dfa0 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1121,6 +1121,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			list of functions. This list can be changed at run
 			time by the set_ftrace_filter file in the debugfs
 			tracing directory.
+			Only built-in functions can be traced when specified
+			this way.
 
 	ftrace_notrace=[function-list]
 			[FTRACE] Do not trace the functions specified in
@@ -1134,6 +1136,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			function-list is a comma separated list of functions
 			that can be changed at run time by the
 			set_graph_function file in the debugfs tracing directory.
+			Only built-in functions can be traced when specified
+			this way.
 
 	ftrace_graph_notrace=[function-list]
 			[FTRACE] Do not trace from the functions specified in
@@ -3521,6 +3525,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 			      trace_options=stacktrace
 
+			Tracer-specific options are ignored when set this way.
+			For example, the 'func_stack_trace' option cannot be
+			set here.
+
 			See also Documentation/trace/ftrace.txt "trace options"
 			section.
 
-- 
2.1.1

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