perf tools: Provide the right bash completion for listing options of perf subcommand subsubcommand

The bash completion gives wrong options for 'perf kvm|kmem|mem|lock|
sched subsubcommand --<TAB>', where 'kvm|kmem|mem|lock|sched' are all
subcommands of perf and 'subsubcommand' is a subcommand of 'kvm|kmem|mem
|lock|sched'. In fact, the result incorrectly lists the bash completion
of 'perf subcommand' rather than 'perf subcommand subsubcommand'.

Example:

Before this patch:

 $ perf kvm record --<TAB>
 --guest          --guestkallsyms  --guestmodules   --guestmount
 --guestvmlinux   --host           --input          --output
 --verbose

As shown above, the result is the options of kvm rather than record.

After this patch:

 $ perf kvm record --<TAB>
 --all-cpus          --cgroup            --delay             --group
 --no-buildid        --output            --quiet             --stat
 --uid
 --branch-any        --count             --event             --intr-regs
 --no-buildid-cache  --period            --raw-samples       --tid
 --verbose
 --branch-filter     --cpu               --filter            --mmap-pages
 --no-inherit        --per-thread        --realtime          --timestamp
 --weight
 --call-graph        --data              --freq
 --no-buffering      --no-samples        --pid
 --running-time      --transaction

As shown above, the result is exactly the options of record as we wished.
Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@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/1426685758-25488-4-git-send-email-yunlong.song@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/perf-completion.sh

@@ -105,9 +105,12 @@ __perf_prev_skip_opts ()
 	local i cmd_ cmds_
 
 	let i=cword-1
-	cmds_=$($cmd --list-cmds)
+	cmds_=$($cmd $1 --list-cmds)
 	prev_skip_opts=()
 	while [ $i -ge 0 ]; do
+		if [[ ${words[i]} == $1 ]]; then
+			return
+		fi
 		for cmd_ in $cmds_; do
 			if [[ ${words[i]} == $cmd_ ]]; then
 				prev_skip_opts=${words[i]}
@@ -146,7 +149,9 @@ __perf_main ()
 		fi
 		# List long option names
 		if [[ $cur == --* ]];  then
-			subcmd=${words[1]}
+			subcmd=$prev_skip_opts
+			__perf_prev_skip_opts $subcmd
+			subcmd=$subcmd" "$prev_skip_opts
 			opts=$($cmd $subcmd --list-opts)
 			__perfcomp "$opts" "$cur"
 		fi