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python/qemu/qmp.py: Fix settimeout operation 

We enabled callers to interface directly with settimeout, but this
reacts poorly with blocking/nonblocking operation; as they are using the
same internal mechanism.

1. Whenever we change the blocking mechanism temporarily, always set it
back to what it was afterwards.

2. Disallow callers from setting a timeout of "0", which means
Non-blocking mode. This is going to create more weird problems than
anybody wants, so just forbid it.

I opt not to coerce '0' to 'None' to maintain the principal of least
surprise in mirroring the semantics of Python's interface.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20201009175123.249009-4-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
This commit is contained in:
John Snow 2020-10-09 13:51:23 -04:00
parent d5cca076c3
commit 39cf73c349
1 changed files with 17 additions and 6 deletions
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23
python/qemu/qmp.py
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@ -164,8 +164,11 @@ class QEMUMonitorProtocol:
retrieved or if some other error occurred.
"""
# Current timeout and blocking status
current_timeout = self.__sock.gettimeout()
# Check for new events regardless and pull them into the cache:
self.__sock.setblocking(False)
self.__sock.settimeout(0) # i.e. setblocking(False)
try:
self.__json_read()
except OSError as err:
@ -173,7 +176,7 @@ class QEMUMonitorProtocol:
if err.errno != errno.EAGAIN:
raise
finally:
self.__sock.setblocking(True)
self.__sock.settimeout(current_timeout)
# Wait for new events, if needed.
# if wait is 0.0, this means "no wait" and is also implicitly false.
@ -187,9 +190,11 @@ class QEMUMonitorProtocol:
except Exception as err:
msg = "Error while reading from socket"
raise QMPConnectError(msg) from err
finally:
self.__sock.settimeout(current_timeout)
if ret is None:
raise QMPConnectError("Error while reading from socket")
self.__sock.settimeout(None)
def __enter__(self) -> 'QEMUMonitorProtocol':
# Implement context manager enter function.
@ -219,7 +224,7 @@ class QEMUMonitorProtocol:
return self.__negotiate_capabilities()
return None
def accept(self, timeout: float = 15.0) -> QMPMessage:
def accept(self, timeout: Optional[float] = 15.0) -> QMPMessage:
"""
Await connection from QMP Monitor and perform capabilities negotiation.
@ -338,13 +343,19 @@ class QEMUMonitorProtocol:
if self.__sockfile:
self.__sockfile.close()
def settimeout(self, timeout: float) -> None:
def settimeout(self, timeout: Optional[float]) -> None:
"""
Set the socket timeout.
@param timeout (float): timeout in seconds, or None.
@param timeout (float): timeout in seconds (non-zero), or None.
@note This is a wrap around socket.settimeout
@raise ValueError: if timeout was set to 0.
"""
if timeout == 0:
msg = "timeout cannot be 0; this engages non-blocking mode."
msg += " Use 'None' instead to disable timeouts."
raise ValueError(msg)
self.__sock.settimeout(timeout)
def get_sock_fd(self) -> int: