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ftrace: improve documentation

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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@gmail.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
walimis 2008-11-28 12:21:19 +08:00 committed by Ingo Molnar
parent 50cdaf08a8
commit c072c24975
1 changed files with 6 additions and 2 deletions
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8
Documentation/ftrace.txt
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@ -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