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=. Document that tracer-specific
options cannot be set on the command line via trace_options.
Document that ftrace cannot do late binding for function
filters.
Signed-off-by: Peter Hurley <pe...@hurleysoftware.com>
---
Documentation/kernel-parameters.txt | 6 ++++++
Documentation/trace/ftrace.txt | 7 +++++--
2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index 4c81a86..d098ead 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1121,6 +1121,7 @@ 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 kernel built-in functions can be filtered.
ftrace_notrace=[function-list]
[FTRACE] Do not trace the functions specified in
@@ -1134,6 +1135,7 @@ 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 kernel built-in functions can be filtered.
ftrace_graph_notrace=[function-list]
[FTRACE] Do not trace from the functions specified in
@@ -3521,6 +3523,10 @@ 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.
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 4da4261..d540273 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -188,7 +188,8 @@ of ftrace. Here is a list of some of the key files:
in with practically no overhead in performance. This also
has a side effect of enabling or disabling specific functions
to be traced. Echoing names of functions into this file
- will limit the trace to only those functions.
+ will limit the trace to only those functions. Only already-
+ loaded functions can be filtered.
This interface also allows for commands to be used. See the
"Filter commands" section for more details.
@@ -208,7 +209,9 @@ of ftrace. Here is a list of some of the key files:
Set a "trigger" function where tracing should start
with the function graph tracer (See the section
- "dynamic ftrace" for more details).
+ "dynamic ftrace" for more details). As with set_ftrace_filter,
+ only names of already-loaded functions can be written to
+ this file.
available_filter_functions:
--
2.1.1
--
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