[PATCH v2 1/1] python/machine.py: refactor shutdown

[John Snow]

This is done primarily to avoid the 'bare except' pattern, which
suppresses ALL exceptions and not just ones that we are anticipating to
see.

Replace this with a pattern that isolates the different kind of shutdown
paradigms and a new fallback shutdown handler that gracefully attempts
one before the other.

Move all of the post-shutdown code into _post_shutdown, and adjust the
main shutdown() function to ALWAYS call the post_shutdown logic no
matter what kind of error we encountered: An expected one (subprocess
wait timeout) or an unexpected one (Everything else).

In cases where we encounter an expected error in the graceful shutdown
timeout, we will not re-raise an exception above shutdown(). Otherwise,
after post_shutdown cleanup, we will.

I anticipate that this WILL lead to additional bug reports filed against
this module, but that is unfortunately somewhat the point: This code
shouldn't be hiding failures that exist elsewhere within the python
code.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 python/qemu/machine.py | 93 +++++++++++++++++++++++++++++-------------
 1 file changed, 65 insertions(+), 28 deletions(-)

diff --git a/python/qemu/machine.py b/python/qemu/machine.py
index 041c615052e..a2abd2c35e3 100644
--- a/python/qemu/machine.py
+++ b/python/qemu/machine.py
@@ -283,6 +283,8 @@ def _post_launch(self):
             self._qmp.accept()
 
     def _post_shutdown(self):
+        self._load_io_log()
+
         if self._qemu_log_file is not None:
             self._qemu_log_file.close()
             self._qemu_log_file = None
@@ -296,6 +298,17 @@ def _post_shutdown(self):
         while len(self._remove_files) > 0:
             self._remove_if_exists(self._remove_files.pop())
 
+        exitcode = self.exitcode()
+        if exitcode is not None and exitcode < 0:
+            msg = 'qemu received signal %i; command: "%s"'
+            if self._qemu_full_args:
+                command = ' '.join(self._qemu_full_args)
+            else:
+                command = ''
+            LOG.warning(msg, -int(exitcode), command)
+
+        self._launched = False
+
     def launch(self):
         """
         Launch the VM and make sure we cleanup and expose the
@@ -344,12 +357,53 @@ def wait(self):
         self._popen.wait()
         if self._qmp:
             self._qmp.close()
-        self._load_io_log()
         self._post_shutdown()
 
-    def shutdown(self, has_quit=False, hard=False):
+    def _hard_shutdown(self) -> None:
         """
-        Terminate the VM and clean up
+        Kill the VM if it is running.
+        """
+        if not self.is_running():
+            return
+
+        self._popen.kill()
+        self._popen.wait(timeout=60)
+
+    def _soft_shutdown(self, has_quit: bool = False, timeout: int = 3) -> None:
+        """
+        Attempt to shutdown the VM gracefully if it is running.
+
+        :param has_quit: When True, don't attempt to issue 'quit' QMP command
+        :param timeout: Timeout for graceful shutdown. Default 3 seconds.
+        """
+        if not self.is_running():
+            return
+
+        if self._qmp is not None:
+            if not has_quit:
+                self._qmp.cmd('quit')
+            self._qmp.close()
+
+        self._popen.wait(timeout=timeout)
+
+    def _do_shutdown(self, has_quit: bool = False, timeout: int = 3) -> None:
+        """
+        Attempt to shutdown the VM gracefully; fallback to a hard shutdown.
+
+        :param has_quit: When True, don't attempt to issue 'quit' QMP command
+        :param timeout: Timeout for graceful shutdown. Default 3 seconds.
+        """
+        try:
+            self._soft_shutdown(has_quit, timeout)
+        except subprocess.TimeoutExpired:
+            self._hard_shutdown()
+        except:
+            self._hard_shutdown()
+            raise
+
+    def shutdown(self, has_quit: bool = False, hard: bool = False) -> None:
+        """
+        Terminate the VM (gracefully if possible) and perform cleanup.
         """
         # If we keep the console socket open, we may deadlock waiting
         # for QEMU to exit, while QEMU is waiting for the socket to
@@ -358,35 +412,18 @@ def shutdown(self, has_quit=False, hard=False):
             self._console_socket.close()
             self._console_socket = None
 
-        if self.is_running():
+        try:
             if hard:
-                self._popen.kill()
-            elif self._qmp:
-                try:
-                    if not has_quit:
-                        self._qmp.cmd('quit')
-                    self._qmp.close()
-                    self._popen.wait(timeout=3)
-                except:
-                    self._popen.kill()
-            self._popen.wait()
-
-        self._load_io_log()
-        self._post_shutdown()
-
-        exitcode = self.exitcode()
-        if exitcode is not None and exitcode < 0 and \
-                not (exitcode == -9 and hard):
-            msg = 'qemu received signal %i: %s'
-            if self._qemu_full_args:
-                command = ' '.join(self._qemu_full_args)
+                self._hard_shutdown()
             else:
-                command = ''
-            LOG.warning(msg, -int(exitcode), command)
-
-        self._launched = False
+                self._do_shutdown(has_quit)
+        finally:
+            self._post_shutdown()
 
     def kill(self):
+        """
+        Terminate the VM forcefully and perform cleanup.
+        """
         self.shutdown(hard=True)
 
     def set_qmp_monitor(self, enabled=True):
-- 
2.21.3