python/machine: raise VMLaunchFailure exception from launch()
This allows us to pack in some extra information about the failure,
which guarantees that if the caller did not *intentionally* cause a
failure (by capturing this Exception), some pretty good clues will be
printed at the bottom of the traceback information.
This will help make failures in the event of a non-negative return code
more obvious when they go unhandled; the current behavior in
_post_shutdown() is to print a warning message only in the event of
signal-based terminations (for negative return codes).
(Note: In Python, catching BaseException instead of Exception catches a
broader array of Exception events, including SystemExit and
KeyboardInterrupt. We do not want to "wrap" such exceptions as a
VMLaunchFailure, because that will 'downgrade' the exception from a
BaseException to a regular Exception. We do, however, want to perform
cleanup in either case, so catch on the broadest scope and
wrap-and-re-raise only in the more targeted scope.)
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 20220201041134.1237016-3-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index 67ab06c..a5972fa 100644
--- a/python/qemu/machine/machine.py
+++ b/python/qemu/machine/machine.py
@@ -74,6 +74,35 @@
"""
+class VMLaunchFailure(QEMUMachineError):
+ """
+ Exception raised when a VM launch was attempted, but failed.
+ """
+ def __init__(self, exitcode: Optional[int],
+ command: str, output: Optional[str]):
+ super().__init__(exitcode, command, output)
+ self.exitcode = exitcode
+ self.command = command
+ self.output = output
+
+ def __str__(self) -> str:
+ ret = ''
+ if self.__cause__ is not None:
+ name = type(self.__cause__).__name__
+ reason = str(self.__cause__)
+ if reason:
+ ret += f"{name}: {reason}"
+ else:
+ ret += f"{name}"
+ ret += '\n'
+
+ if self.exitcode is not None:
+ ret += f"\tExit code: {self.exitcode}\n"
+ ret += f"\tCommand: {self.command}\n"
+ ret += f"\tOutput: {self.output}\n"
+ return ret
+
+
class AbnormalShutdown(QEMUMachineError):
"""
Exception raised when a graceful shutdown was requested, but not performed.
@@ -397,7 +426,7 @@
try:
self._launch()
- except:
+ except BaseException as exc:
# We may have launched the process but it may
# have exited before we could connect via QMP.
# Assume the VM didn't launch or is exiting.
@@ -408,11 +437,15 @@
else:
self._post_shutdown()
- LOG.debug('Error launching VM')
- if self._qemu_full_args:
- LOG.debug('Command: %r', ' '.join(self._qemu_full_args))
- if self._iolog:
- LOG.debug('Output: %r', self._iolog)
+ if isinstance(exc, Exception):
+ raise VMLaunchFailure(
+ exitcode=self.exitcode(),
+ command=' '.join(self._qemu_full_args),
+ output=self._iolog
+ ) from exc
+
+ # Don't wrap 'BaseException'; doing so would downgrade
+ # that exception. However, we still want to clean up.
raise
def _launch(self) -> None: