perf record: Don't exit in live mode when no tracepoints are enabled

With this I was able to actually test Tom Zanussi's two previous patches
in my usual perf testing ways, i.e. without any tracepoints activated.

Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -666,12 +666,15 @@ static int __cmd_record(int argc, const char **argv)
 						     nr_counters,
 						     process_synthesized_event,
 						     session);
-		if (err <= 0) {
-			pr_err("Couldn't record tracing data.\n");
-			return err;
-		}
-
-		advance_output(err);
+		/*
+		 * FIXME err <= 0 here actually means that there were no tracepoints
+		 * so its not really an error, just that we don't need to synthesize
+		 * anything.
+		 * We really have to return this more properly and also propagate
+		 * errors that now are calling die()
+		 */
+		if (err > 0)
+			advance_output(err);
 	}
 
 	machine = perf_session__find_host_machine(session);