perf probe: Add filters support for available functions

Add filters support for available function list.

Default filter is "!_*" for filtering out local-purpose symbols.

e.g.:
 # perf probe --filter="add*" -F
add_disk
add_disk_randomness
add_input_randomness
add_interrupt_randomness
add_memory
add_page_to_unevictable_list
add_page_wait_queue
...

Cc: 2nddept-manager@sdl.hitachi.co.jp
Cc: Chase Douglas <chase.douglas@canonical.com>
Cc: Franck Bui-Huu <fbuihuu@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20110120141545.25915.85930.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/Documentation/perf-probe.txt b/tools/perf/Documentation/perf-probe.txt
index 32fb18f..81c3220 100644
--- a/tools/perf/Documentation/perf-probe.txt
+++ b/tools/perf/Documentation/perf-probe.txt
@@ -78,10 +78,11 @@
 	Show available functions in given module or kernel.
 
 --filter=FILTER::
-	(Only for --vars) Set filter for variables. FILTER is a combination of
-	glob pattern, see FILTER PATTERN for details.
-	Default FILTER is "!__k???tab_* & !__crc_*".
-	If several filters are specified, only the last filter is valid.
+	(Only for --vars and --funcs) Set filter. FILTER is a combination of glob
+	pattern, see FILTER PATTERN for detail.
+	Default FILTER is "!__k???tab_* & !__crc_*" for --vars, and "!_*"
+	for --funcs.
+	If several filters are specified, only the last filter is used.
 
 -f::
 --force::