tracing: Add function probe to trigger a ftrace dump to console

Add the "dump" command to have the ftrace buffer dumped to console if
a function is hit. This is useful when debugging a tripple fault,
where you have an idea of a function that is called just before the
tripple fault occurs, and can tell ftrace to dump its content out
to the console before it continues.

Format is:

  <function>:dump

echo 'bad_address:dump' > /debug/tracing/set_ftrace_filter

To remove this:

echo '!bad_address:dump' > /debug/tracing/set_ftrace_filter

Requested-by: Luis Claudio R. Goncalves <lclaudio@uudg.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index bfe8c29b1f1d..cc9ec57e157c 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -2430,6 +2430,13 @@ The following commands are supported:
    echo '!schedule:disable_event:sched:sched_switch' > \
          set_ftrace_filter
 
+- dump
+  When the function is hit, it will dump the contents of the ftrace
+  ring buffer to the console. This is useful if you need to debug
+  something, and want to dump the trace when a certain function
+  is hit. Perhaps its a function that is called before a tripple
+  fault happens and does not allow you to get a regular dump.
+
 trace_pipe
 ----------