perf tools: Fix the bash completion problem of 'perf --*'

The perf-completion.sh uses a predefined string '--help --version
--exec-path --html-path --paginate --no-pager --perf-dir --work-tree
--debugfs-dir' for the bash completion of 'perf --*', which has two
problems:

 Problem 1: If the options of perf are changed (see handle_options() in
 perf.c), the perf-completion.sh has to be changed at the same time. If
 not, the bash completion of 'perf --*' and the options which perf
 really supports will be inconsistent.

 Problem 2: When typing another single character after 'perf --', e.g.
 'h', and hit TAB key to get the bash completion of 'perf --h', the
 character 'h' disappears at once. This is not what we want, we wish the
 bash completion can return '--help --html-path' and then we can
 continue to choose one.

 To solve this problem, we add '--list-opts' to perf, which now supports
 'perf --list-opts' directly, and its result can be used in bash
 completion now.

Example:

 Before this patch:

 $ perf --h                 <-- hit TAB key after character 'h'
 $ perf --                  <-- 'h' disappears and no required result

 After this patch:

 $ perf --h                 <-- hit TAB key after character 'h'
 --help       --html-path   <-- the required result

Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1425032491-20224-8-git-send-email-yunlong.song@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/perf-completion.sh b/tools/perf/perf-completion.sh
index 3356984..c2595e9 100644
--- a/tools/perf/perf-completion.sh
+++ b/tools/perf/perf-completion.sh
@@ -110,13 +110,11 @@
 	# List perf subcommands or long options
 	if [ $cword -eq 1 ]; then
 		if [[ $cur == --* ]]; then
-			__perfcomp '--help --version \
-			--exec-path --html-path --paginate --no-pager \
-			--perf-dir --work-tree --debugfs-dir' -- "$cur"
+			cmds=$($cmd --list-opts)
 		else
 			cmds=$($cmd --list-cmds)
-			__perfcomp "$cmds" "$cur"
 		fi
+		__perfcomp "$cmds" "$cur"
 	# List possible events for -e option
 	elif [[ $prev == "-e" && "${words[1]}" == @(record|stat|top) ]]; then
 		evts=$($cmd list --raw-dump)