[PATCH v4 13/16] python/machine.py: fix _popen access

[John Snow]

As always, Optional[T] causes problems with unchecked access. Add a
helper that asserts the pipe is present before we attempt to talk with
it.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
---
 python/qemu/machine.py | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/python/qemu/machine.py b/python/qemu/machine.py
index cb3db1f66a..c189fa4e28 100644
--- a/python/qemu/machine.py
+++ b/python/qemu/machine.py
@@ -114,7 +114,7 @@ def __init__(self, binary, args=None, wrapper=None, 
name=None,
         # Runstate
         self._qemu_log_path = None
         self._qemu_log_file = None
-        self._popen = None
+        self._popen: Optional['subprocess.Popen[bytes]'] = None
         self._events = []
         self._iolog = None
         self._qmp_set = True   # Enable QMP monitor by default.
@@ -227,6 +227,12 @@ def is_running(self):
         """Returns true if the VM is running."""
         return self._popen is not None and self._popen.poll() is None
 
+    @property
+    def _subp(self) -> 'subprocess.Popen[bytes]':
+        if self._popen is None:
+            raise QEMUMachineError('Subprocess pipe not present')
+        return self._popen
+
     def exitcode(self):
         """Returns the exit code if possible, or None."""
         if self._popen is None:
@@ -237,7 +243,7 @@ def get_pid(self):
         """Returns the PID of the running process, or None."""
         if not self.is_running():
             return None
-        return self._popen.pid
+        return self._subp.pid
 
     def _load_io_log(self):
         if self._qemu_log_path is not None:
@@ -369,7 +375,7 @@ def wait(self):
         """
         Wait for the VM to power off
         """
-        self._popen.wait()
+        self._subp.wait()
         if self._qmp_connection:
             self._qmp.close()
         self._post_shutdown()
@@ -381,8 +387,8 @@ def _hard_shutdown(self) -> None:
         if not self.is_running():
             return
 
-        self._popen.kill()
-        self._popen.wait(timeout=60)
+        self._subp.kill()
+        self._subp.wait(timeout=60)
 
     def _soft_shutdown(self, has_quit: bool = False, timeout: int = 3) -> None:
         """
@@ -407,7 +413,7 @@ def _soft_shutdown(self, has_quit: bool = False, timeout: 
int = 3) -> None:
                         raise
             self._qmp.close()
 
-        self._popen.wait(timeout=timeout)
+        self._subp.wait(timeout=timeout)
 
     def _do_shutdown(self, has_quit: bool = False, timeout: int = 3) -> None:
         """
-- 
2.21.3