perf record: Fix the profiling of existing pid or whole box

Perf record bails if no command argument is provided, so you can't use
naked -a or -p to profile a running task or the whole box.

Allow foreground profiling of an existing pid or the entire system.

[ Impact: fix command option handling bug ]

Signed-off-by: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/perf_counter/builtin-record.c

@@ -354,7 +354,7 @@ static int __cmd_record(int argc, const char **argv)
 	signal(SIGCHLD, sig_handler);
 	signal(SIGINT, sig_handler);
 
-	if (target_pid == -1) {
+	if (target_pid == -1 && argc) {
 		pid = fork();
 		if (pid < 0)
 			perror("failed to fork");
@@ -430,7 +430,7 @@ int cmd_record(int argc, const char **argv, const char *prefix)
 	create_events_help(events_help_msg);
 
 	argc = parse_options(argc, argv, options, record_usage, 0);
-	if (!argc)
+	if (!argc && target_pid == -1 && !system_wide)
 		usage_with_options(record_usage, options);
 
 	if (!nr_counters) {