perf data: Show error message when conversion failed

Show message when errors occurred during conversion setup and conversion
process.

Before this patch:
  $ ./perf data convert --to-ctf=ctf
  $ echo $?
  255

After this patch:
  $ ./perf data convert --to-ctf=ctf
  Error during conversion setup.

Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jeremie Galarneau <jgalar@efficios.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-xvhr1vf7zav9kkeo9w1hv4uk@git.kernel.org
Link: http://lkml.kernel.org/r/1429372220-6406-2-git-send-email-jolsa@kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/data-convert-bt.c

@@ -837,6 +837,8 @@ int bt_convert__perf2ctf(const char *input, const char *path, bool force)
 	err = perf_session__process_events(session);
 	if (!err)
 		err = bt_ctf_stream_flush(cw->stream);
+	else
+		pr_err("Error during conversion.\n");
 
 	fprintf(stderr,
 		"[ perf data convert: Converted '%s' into CTF data '%s' ]\n",
@@ -847,11 +849,15 @@ int bt_convert__perf2ctf(const char *input, const char *path, bool force)
 		(double) c.events_size / 1024.0 / 1024.0,
 		c.events_count);
 
-	/* its all good */
-free_session:
 	perf_session__delete(session);
+	ctf_writer__cleanup(cw);
 
+	return err;
+
+free_session:
+	perf_session__delete(session);
 free_writer:
 	ctf_writer__cleanup(cw);
+	pr_err("Error during conversion setup.\n");
 	return err;
 }