trace-cmd: Add --func-stack option to enable function stack trace

Added --func-stack option to trace-cmd record, that will enable the
function stack tracing, but only if the -l option (limit functions)
is used, and succeeds in filtering functions. It is known that running
the function stack trace on all functions can livelock the machine.

The output now looks like this:

          <idle>-0     [002] 64003.696572: function:             schedule
          <idle>-0     [002] 64003.696577: kernel_stack:         <stack trace>
=> cpu_idle (ffffffff8100a38c)
=> start_secondary (ffffffff814ab828)
       trace-cmd-4132  [003] 64003.696632: function:             schedule
       trace-cmd-4132  [003] 64003.696637: kernel_stack:         <stack trace>

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

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/trace-cmd-record.1.txt b/Documentation/trace-cmd-record.1.txt
index 87e4f97..b78182a 100644
--- a/Documentation/trace-cmd-record.1.txt
+++ b/Documentation/trace-cmd-record.1.txt
@@ -64,6 +64,13 @@ OPTIONS
 => cpu_idle (ffffffff8100a38c)
 => start_secondary (ffffffff814ab828)
 
+*--func-stack*::
+    Enable a stack trace on all functions. Note this is only applicable
+    for the "function" plugin tracer, and will only take effect if the
+    -l option is used and succeeds in limiting functions. If the function
+    tracer is not filtered, and the stack trace is enabled, you can live
+    lock the machine.
+
 *-f* 'filter'::
     Specify a filter for the previous event. This must come after a *-e*. This
     will filter what events get recorded based on the content of the event.