Merge remote-tracking branch 'remotes/philmd-gitlab/tags/python-next-20200714' into staging

Python patches for 5.1

- Reduce race conditions on QEMUMachine::shutdown()

 1. Remove the "bare except" pattern in the existing shutdown code,
    which can mask problems and make debugging difficult.
 2. Ensure that post-shutdown cleanup is always performed, even when
    graceful termination fails.
 3. Unify cleanup paths such that no matter how the VM is terminated,
    the same functions and steps are always taken to reset the object
    state.
 4. Rewrite shutdown() such that any error encountered when attempting
    a graceful shutdown will be raised as an AbnormalShutdown exception.
    The pythonic idiom is to allow the caller to decide if this is a
    problem or not.

- Modify part of the python/qemu library to comply with:

  . mypy --strict
  . pylint
  . flake8

- Script for the TCG Continuous Benchmarking project that uses
  callgrind to dissect QEMU execution into three main phases:

  . code generation
  . JIT execution
  . helpers execution

CI jobs results:
. https://cirrus-ci.com/build/5421349961203712
. https://gitlab.com/philmd/qemu/-/pipelines/166556001
. https://travis-ci.org/github/philmd/qemu/builds/708102347

# gpg: Signature made Tue 14 Jul 2020 21:40:05 BST
# gpg:                using RSA key FAABE75E12917221DCFD6BB2E3E32C2CDEADC0DE
# gpg: Good signature from "Philippe Mathieu-Daudé (F4BUG) <f4bug@amsat.org>" [full]
# Primary key fingerprint: FAAB E75E 1291 7221 DCFD  6BB2 E3E3 2C2C DEAD C0DE

* remotes/philmd-gitlab/tags/python-next-20200714:
  python/qmp.py: add QMPProtocolError
  python/qmp.py: add casts to JSON deserialization
  python/qmp.py: Do not return None from cmd_obj
  python/qmp.py: re-absorb MonitorResponseError
  iotests.py: use qemu.qmp type aliases
  python/qmp.py: Define common types
  python/machine.py: change default wait timeout to 3 seconds
  python/machine.py: re-add sigkill warning suppression
  python/machine.py: split shutdown into hard and soft flavors
  tests/acceptance: Don't test reboot on cubieboard
  tests/acceptance: wait() instead of shutdown() where appropriate
  python/machine.py: Make wait() call shutdown()
  python/machine.py: Add a configurable timeout to shutdown()
  python/machine.py: Prohibit multiple shutdown() calls
  python/machine.py: Perform early cleanup for wait() calls, too
  python/machine.py: Add _early_cleanup hook
  python/machine.py: Close QMP socket in cleanup
  python/machine.py: consolidate _post_shutdown()
  scripts/performance: Add dissect.py script

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 182 insertions, 59 deletions

diff --git a/python/qemu/machine.py b/python/qemu/machine.py
index c25f0b4..80c4d4a 100644
--- a/python/qemu/machine.py
+++ b/python/qemu/machine.py
@@ -22,6 +22,7 @@ import logging
 import os
 import subprocess
 import shutil
+import signal
 import socket
 import tempfile
 from typing import Optional, Type
@@ -49,17 +50,10 @@ class QEMUMachineAddDeviceError(QEMUMachineError):
     """
 
 
-class MonitorResponseError(qmp.QMPError):
+class AbnormalShutdown(QEMUMachineError):
     """
-    Represents erroneous QMP monitor reply
+    Exception raised when a graceful shutdown was requested, but not performed.
     """
-    def __init__(self, reply):
-        try:
-            desc = reply["error"]["desc"]
-        except KeyError:
-            desc = reply
-        super().__init__(desc)
-        self.reply = reply
 
 
 class QEMUMachine:
@@ -127,6 +121,7 @@ class QEMUMachine:
         self._console_address = None
         self._console_socket = None
         self._remove_files = []
+        self._user_killed = False
         self._console_log_path = console_log
         if self._console_log_path:
             # In order to log the console, buffering needs to be enabled.
@@ -294,6 +289,19 @@ class QEMUMachine:
             self._qmp.accept()
 
     def _post_shutdown(self):
+        """
+        Called to cleanup the VM instance after the process has exited.
+        May also be called after a failed launch.
+        """
+        # Comprehensive reset for the failed launch case:
+        self._early_cleanup()
+
+        if self._qmp:
+            self._qmp.close()
+            self._qmp = None
+
+        self._load_io_log()
+
         if self._qemu_log_file is not None:
             self._qemu_log_file.close()
             self._qemu_log_file = None
@@ -307,6 +315,19 @@ class QEMUMachine:
         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
+                and not (self._user_killed and exitcode == -signal.SIGKILL)):
+            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._user_killed = False
+        self._launched = False
+
     def launch(self):
         """
         Launch the VM and make sure we cleanup and expose the
@@ -322,7 +343,7 @@ class QEMUMachine:
             self._launch()
             self._launched = True
         except:
-            self.shutdown()
+            self._post_shutdown()
 
             LOG.debug('Error launching VM')
             if self._qemu_full_args:
@@ -348,19 +369,12 @@ class QEMUMachine:
                                        close_fds=False)
         self._post_launch()
 
-    def wait(self):
-        """
-        Wait for the VM to power off
+    def _early_cleanup(self) -> None:
         """
-        self._popen.wait()
-        if self._qmp:
-            self._qmp.close()
-        self._load_io_log()
-        self._post_shutdown()
+        Perform any cleanup that needs to happen before the VM exits.
 
-    def shutdown(self, has_quit=False, hard=False):
-        """
-        Terminate the VM and clean up
+        May be invoked by both soft and hard shutdown in failover scenarios.
+        Called additionally by _post_shutdown for comprehensive cleanup.
         """
         # If we keep the console socket open, we may deadlock waiting
         # for QEMU to exit, while QEMU is waiting for the socket to
@@ -369,37 +383,105 @@ class QEMUMachine:
             self._console_socket.close()
             self._console_socket = None
 
-        if self.is_running():
-            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()
+    def _hard_shutdown(self) -> None:
+        """
+        Perform early cleanup, kill the VM, and wait for it to terminate.
 
-        self._load_io_log()
-        self._post_shutdown()
+        :raise subprocess.Timeout: When timeout is exceeds 60 seconds
+            waiting for the QEMU process to terminate.
+        """
+        self._early_cleanup()
+        self._popen.kill()
+        self._popen.wait(timeout=60)
 
-        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)
-            else:
-                command = ''
-            LOG.warning(msg, -int(exitcode), command)
+    def _soft_shutdown(self, has_quit: bool = False,
+                       timeout: Optional[int] = 3) -> None:
+        """
+        Perform early cleanup, attempt to gracefully shut down the VM, and wait
+        for it to terminate.
 
-        self._launched = False
+        :param has_quit: When True, don't attempt to issue 'quit' QMP command
+        :param timeout: Optional timeout in seconds for graceful shutdown.
+                        Default 3 seconds, A value of None is an infinite wait.
+
+        :raise ConnectionReset: On QMP communication errors
+        :raise subprocess.TimeoutExpired: When timeout is exceeded waiting for
+            the QEMU process to terminate.
+        """
+        self._early_cleanup()
+
+        if self._qmp is not None:
+            if not has_quit:
+                # Might raise ConnectionReset
+                self._qmp.cmd('quit')
+
+        # May raise subprocess.TimeoutExpired
+        self._popen.wait(timeout=timeout)
+
+    def _do_shutdown(self, has_quit: bool = False,
+                     timeout: Optional[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: Optional timeout in seconds for graceful shutdown.
+                        Default 3 seconds, A value of None is an infinite wait.
+
+        :raise AbnormalShutdown: When the VM could not be shut down gracefully.
+            The inner exception will likely be ConnectionReset or
+            subprocess.TimeoutExpired. In rare cases, non-graceful termination
+            may result in its own exceptions, likely subprocess.TimeoutExpired.
+        """
+        try:
+            self._soft_shutdown(has_quit, timeout)
+        except Exception as exc:
+            self._hard_shutdown()
+            raise AbnormalShutdown("Could not perform graceful shutdown") \
+                from exc
+
+    def shutdown(self, has_quit: bool = False,
+                 hard: bool = False,
+                 timeout: Optional[int] = 3) -> None:
+        """
+        Terminate the VM (gracefully if possible) and perform cleanup.
+        Cleanup will always be performed.
+
+        If the VM has not yet been launched, or shutdown(), wait(), or kill()
+        have already been called, this method does nothing.
+
+        :param has_quit: When true, do not attempt to issue 'quit' QMP command.
+        :param hard: When true, do not attempt graceful shutdown, and
+                     suppress the SIGKILL warning log message.
+        :param timeout: Optional timeout in seconds for graceful shutdown.
+                        Default 3 seconds, A value of None is an infinite wait.
+        """
+        if not self._launched:
+            return
+
+        try:
+            if hard:
+                self._user_killed = True
+                self._hard_shutdown()
+            else:
+                self._do_shutdown(has_quit, timeout=timeout)
+        finally:
+            self._post_shutdown()
 
     def kill(self):
+        """
+        Terminate the VM forcefully, wait for it to exit, and perform cleanup.
+        """
         self.shutdown(hard=True)
 
+    def wait(self, timeout: Optional[int] = 3) -> None:
+        """
+        Wait for the VM to power off and perform post-shutdown cleanup.
+
+        :param timeout: Optional timeout in seconds.
+                        Default 3 seconds, A value of None is an infinite wait.
+        """
+        self.shutdown(has_quit=True, timeout=timeout)
+
     def set_qmp_monitor(self, enabled=True):
         """
         Set the QMP monitor.
@@ -438,7 +520,7 @@ class QEMUMachine:
         if reply is None:
             raise qmp.QMPError("Monitor is closed")
         if "error" in reply:
-            raise MonitorResponseError(reply)
+            raise qmp.QMPResponseError(reply)
         return reply["return"]
 
     def get_qmp_event(self, wait=False):
diff --git a/python/qemu/qmp.py b/python/qemu/qmp.py
index e64b6b5..7935dab 100644
--- a/python/qemu/qmp.py
+++ b/python/qemu/qmp.py
@@ -12,13 +12,32 @@ import errno
 import socket
 import logging
 from typing import (
+    Any,
+    cast,
+    Dict,
     Optional,
     TextIO,
     Type,
+    Tuple,
+    Union,
 )
 from types import TracebackType
 
 
+# QMPMessage is a QMP Message of any kind.
+# e.g. {'yee': 'haw'}
+#
+# QMPReturnValue is the inner value of return values only.
+# {'return': {}} is the QMPMessage,
+# {} is the QMPReturnValue.
+QMPMessage = Dict[str, Any]
+QMPReturnValue = Dict[str, Any]
+
+InternetAddrT = Tuple[str, str]
+UnixAddrT = str
+SocketAddrT = Union[InternetAddrT, UnixAddrT]
+
+
 class QMPError(Exception):
     """
     QMP base exception
@@ -43,6 +62,25 @@ class QMPTimeoutError(QMPError):
     """
 
 
+class QMPProtocolError(QMPError):
+    """
+    QMP protocol error; unexpected response
+    """
+
+
+class QMPResponseError(QMPError):
+    """
+    Represents erroneous QMP monitor reply
+    """
+    def __init__(self, reply: QMPMessage):
+        try:
+            desc = reply['error']['desc']
+        except KeyError:
+            desc = reply
+        super().__init__(desc)
+        self.reply = reply
+
+
 class QEMUMonitorProtocol:
     """
     Provide an API to connect to QEMU via QEMU Monitor Protocol (QMP) and then
@@ -99,7 +137,10 @@ class QEMUMonitorProtocol:
             data = self.__sockfile.readline()
             if not data:
                 return None
-            resp = json.loads(data)
+            # By definition, any JSON received from QMP is a QMPMessage,
+            # and we are asserting only at static analysis time that it
+            # has a particular shape.
+            resp: QMPMessage = json.loads(data)
             if 'event' in resp:
                 self.logger.debug("<<< %s", resp)
                 self.__events.append(resp)
@@ -194,22 +235,18 @@ class QEMUMonitorProtocol:
         self.__sockfile = self.__sock.makefile(mode='r')
         return self.__negotiate_capabilities()
 
-    def cmd_obj(self, qmp_cmd):
+    def cmd_obj(self, qmp_cmd: QMPMessage) -> QMPMessage:
         """
         Send a QMP command to the QMP Monitor.
 
         @param qmp_cmd: QMP command to be sent as a Python dict
-        @return QMP response as a Python dict or None if the connection has
-                been closed
+        @return QMP response as a Python dict
         """
         self.logger.debug(">>> %s", qmp_cmd)
-        try:
-            self.__sock.sendall(json.dumps(qmp_cmd).encode('utf-8'))
-        except OSError as err:
-            if err.errno == errno.EPIPE:
-                return None
-            raise err
+        self.__sock.sendall(json.dumps(qmp_cmd).encode('utf-8'))
         resp = self.__json_read()
+        if resp is None:
+            raise QMPConnectError("Unexpected empty reply from server")
         self.logger.debug("<<< %s", resp)
         return resp
 
@@ -233,9 +270,13 @@ class QEMUMonitorProtocol:
         Build and send a QMP command to the monitor, report errors if any
         """
         ret = self.cmd(cmd, kwds)
-        if "error" in ret:
-            raise Exception(ret['error']['desc'])
-        return ret['return']
+        if 'error' in ret:
+            raise QMPResponseError(ret)
+        if 'return' not in ret:
+            raise QMPProtocolError(
+                "'return' key not found in QMP response '{}'".format(str(ret))
+            )
+        return cast(QMPReturnValue, ret['return'])
 
     def pull_event(self, wait=False):
         """