tracing/kprobes: Disable kprobe events by default after creation

Disable newly created kprobe events by default, not to disturb
another user using ftrace. "Disturb" means when someone is using
ftrace and another user tries to use perf-tools, (in near
future) if he defines new kprobe event via perf-tools, then new
events will mess up the frace buffer. Fix this to allow proper
and transparent kprobes events concurrent usage between ftrace
users and perf users.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jason Baron <jbaron@redhat.com>
Cc: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <20090914204937.18779.59422.stgit@dhcp-100-2-132.bos.redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
index 6521681e7838..9b8f7c6040a7 100644
--- a/Documentation/trace/kprobetrace.txt
+++ b/Documentation/trace/kprobetrace.txt
@@ -122,8 +122,15 @@ print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->ip, REC->dfd, R
 
   echo > /sys/kernel/debug/tracing/kprobe_events
 
- This clears all probe points. and you can see the traced information via
-/sys/kernel/debug/tracing/trace.
+ This clears all probe points.
+
+ Right after definition, each event is disabled by default. For tracing these
+events, you need to enable it.
+
+  echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable
+  echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable
+
+ And you can see the traced information via /sys/kernel/debug/tracing/trace.
 
   cat /sys/kernel/debug/tracing/trace
 # tracer: nop