linux-kernel - Re: [PATCH 1/1] ftrace: improve document

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Date:	Fri, 28 Nov 2008 13:16:37 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	walimis <walimisdev@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ftrace: improve document


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> On Fri, 28 Nov 2008, walimis wrote:
> > 
> > Signed-off-by: walimis <walimisdev@...il.com>
> > Reviewed-by: Ingo Molnar <mingo@...e.hu>
> > Reviewed-by: Steven Rostedt <srostedt@...hat.com>
> 
> Acked-by: Steven Rostedt <srostedt@...hat.com>

applied it to tip/tracing/ftrace, thanks guys! (Changed the commit log a 
bit, see the final commit below.)

	Ingo

-------------->
>From c072c24975ec4f0ccfcb6f5c8a8040b6eb75ef8f Mon Sep 17 00:00:00 2001
From: walimis <walimisdev@...il.com>
Date: Fri, 28 Nov 2008 12:21:19 +0800
Subject: [PATCH] ftrace: improve documentation

Impact: extend documentation with 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 them naively 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 filenames to set_ftrace_filter, not the
intended "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 escape 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@...il.com>
Acked-by: Steven Rostedt <srostedt@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 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
--
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