python/qemu/qtest: Check before accessing _qtest

It can be None; so add assertions or exceptions where appropriate to
guard the access accordingly.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200514055403.18902-30-jsnow@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/python/qemu/qtest.py b/python/qemu/qtest.py
index 4c88590eb0..888c8bd2f6 100644
--- a/python/qemu/qtest.py
+++ b/python/qemu/qtest.py
@@ -121,7 +121,8 @@ class QEMUQtestMachine(QEMUMachine):
         super()._pre_launch()
         self._qtest = QEMUQtestProtocol(self._qtest_path, server=True)
 
-    def _post_launch(self):
+    def _post_launch(self) -> None:
+        assert self._qtest is not None
         super()._post_launch()
         self._qtest.accept()
 
@@ -129,6 +130,13 @@ class QEMUQtestMachine(QEMUMachine):
         super()._post_shutdown()
         self._remove_if_exists(self._qtest_path)
 
-    def qtest(self, cmd):
-        '''Send a qtest command to guest'''
+    def qtest(self, cmd: str) -> str:
+        """
+        Send a qtest command to the guest.
+
+        :param cmd: qtest command to send
+        :return: qtest server response
+        """
+        if self._qtest is None:
+            raise RuntimeError("qtest socket not available")
         return self._qtest.cmd(cmd)