[PATCH 1/1] ftrace: improve document

[walimis <walimisdev@gmail.com>]

Impact: add notice of using wild cards correctly

We know that we can use wild cards to set set_ftrace_filter, but there's
problem when using such as "echo h* > /debug/tracing/set_ftrace_filter".
If there are files named with "h" prefix in current directory, echo "h*"
will echo these files' name to set_ftrace_filter, not "h*".
For example:
$cat /debug/tracing/available_filter_functions |grep ^hr |wc -l
23
$ls
$touch hraa hrdd
$ls
hraa  hrdd
$echo hr* > /debug/tracing/set_ftrace_filter
$cat /debug/tracing/set_ftrace_filter

No output in /debug/tracing/set_ftrace_filter!
If we use '' to enclose wild cards, it works:

$ls
hraa  hrdd
$echo "hr*" > /debug/tracing/set_ftrace_filter
$cat /debug/tracing/set_ftrace_filter |wc -l
23

This problem can lead to unexpected result if current directory has a
lot of files.

Signed-off-by: walimis <walimisdev@gmail.com>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Reviewed-by: Steven Rostedt <srostedt@redhat.com>
---
 Documentation/ftrace.txt |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/Documentation/ftrace.txt b/Documentation/ftrace.txt
index de05042..803b131 100644
--- a/Documentation/ftrace.txt
+++ b/Documentation/ftrace.txt
@@ -1251,7 +1251,11 @@ These are the only wild cards which are supported.
 
   <match>*<match> will not work.
 
- # echo hrtimer_* > /debug/tracing/set_ftrace_filter
+Note: It is better to use quotes to enclose the wild cards, otherwise
+  the shell may expand the parameters into names of files in the local
+  directory.
+
+ # echo 'hrtimer_*' > /debug/tracing/set_ftrace_filter
 
 Produces:
 
@@ -1306,7 +1310,7 @@ Again, now we want to append.
  # echo sys_nanosleep > /debug/tracing/set_ftrace_filter
  # cat /debug/tracing/set_ftrace_filter
 sys_nanosleep
- # echo hrtimer_* >> /debug/tracing/set_ftrace_filter
+ # echo 'hrtimer_*' >> /debug/tracing/set_ftrace_filter
  # cat /debug/tracing/set_ftrace_filter
 hrtimer_run_queues
 hrtimer_run_pending
-- 
1.6.0.3