perf record: We should fork only if a program was specified to run

IOW: Now 'perf record -a' works, this was a bug introduced in:

856e96608a
"perf record: Properly synchronize child creation"

Also fix the -C usage, i.e. allow for profiling all the tasks in
one CPU.

Reported-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1261957026-15580-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/builtin-record.c

@@ -402,7 +402,7 @@ static void atexit_header(void)
 	perf_header__write(&session->header, output, true);
 }
 
-static int __cmd_record(int argc __used, const char **argv)
+static int __cmd_record(int argc, const char **argv)
 {
 	int i, counter;
 	struct stat st;
@@ -411,6 +411,7 @@ static int __cmd_record(int argc __used, const char **argv)
 	int err;
 	unsigned long waking = 0;
 	int child_ready_pipe[2], go_pipe[2];
+	const bool forks = target_pid == -1 && argc > 0;
 	char buf;
 
 	page_size = sysconf(_SC_PAGE_SIZE);
@@ -422,7 +423,7 @@ static int __cmd_record(int argc __used, const char **argv)
 	signal(SIGCHLD, sig_handler);
 	signal(SIGINT, sig_handler);
 
-	if (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0) {
+	if (forks && (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0)) {
 		perror("failed to create pipes");
 		exit(-1);
 	}
@@ -483,7 +484,7 @@ static int __cmd_record(int argc __used, const char **argv)
 
 	atexit(atexit_header);
 
-	if (target_pid == -1) {
+	if (forks) {
 		pid = fork();
 		if (pid < 0) {
 			perror("failed to fork");
@@ -550,7 +551,7 @@ static int __cmd_record(int argc __used, const char **argv)
 			return err;
 	}
 
-	if (!system_wide)
+	if (!system_wide && profile_cpu == -1)
 		event__synthesize_thread(pid, process_synthesized_event,
 					 session);
 	else
@@ -569,6 +570,7 @@ static int __cmd_record(int argc __used, const char **argv)
 	/*
 	 * Let the child rip
 	 */
+	if (forks)
 		close(go_pipe[1]);
 
 	for (;;) {
@@ -667,7 +669,7 @@ int cmd_record(int argc, const char **argv, const char *prefix __used)
 
 	argc = parse_options(argc, argv, options, record_usage,
 			    PARSE_OPT_STOP_AT_NON_OPTION);
-	if (!argc && target_pid == -1 && (!system_wide || profile_cpu == -1))
+	if (!argc && target_pid == -1 && !system_wide && profile_cpu == -1)
 		usage_with_options(record_usage, options);
 
 	symbol__init();