| Message ID | 20220124180626.627718-5-jsnow@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Python: Improvements for iotest 040,041 | expand |
On 24.01.22 19:06, John Snow wrote: > The synchronous QMP library would bind to the server address during > __init__(). The new library delays this to the accept() call, because > binding occurs inside of the call to start_[unix_]server(), which is an > async method -- so it cannot happen during __init__ anymore. > > Python 3.7+ adds the ability to create the server (and thus the bind() > call) and begin the active listening in separate steps, but we don't > have that functionality in 3.6, our current minimum. > > Therefore ... Add a temporary workaround that allows the synchronous > version of the client to bind the socket in advance, guaranteeing that > there will be a UNIX socket in the filesystem ready for the QEMU client > to connect to without a race condition. > > (Yes, it's a bit ugly. Fixing it more nicely will have to wait until our > minimum Python version is 3.7+.) I mean. Looks good to me? Not quite enough for an R-b, I’d say, and you don’t really need an A-b from me on this, but looks good to me! O:) > Signed-off-by: John Snow <jsnow@redhat.com> > --- > python/qemu/aqmp/legacy.py | 3 +++ > python/qemu/aqmp/protocol.py | 41 +++++++++++++++++++++++++++++++++--- > 2 files changed, 41 insertions(+), 3 deletions(-)
On Thu, Jan 27, 2022 at 10:50 AM Hanna Reitz <hreitz@redhat.com> wrote: > > On 24.01.22 19:06, John Snow wrote: > > The synchronous QMP library would bind to the server address during > > __init__(). The new library delays this to the accept() call, because > > binding occurs inside of the call to start_[unix_]server(), which is an > > async method -- so it cannot happen during __init__ anymore. > > > > Python 3.7+ adds the ability to create the server (and thus the bind() > > call) and begin the active listening in separate steps, but we don't > > have that functionality in 3.6, our current minimum. > > > > Therefore ... Add a temporary workaround that allows the synchronous > > version of the client to bind the socket in advance, guaranteeing that > > there will be a UNIX socket in the filesystem ready for the QEMU client > > to connect to without a race condition. > > > > (Yes, it's a bit ugly. Fixing it more nicely will have to wait until our > > minimum Python version is 3.7+.) > > I mean. Looks good to me? Not quite enough for an R-b, I’d say, and > you don’t really need an A-b from me on this, but looks good to me! O:) > Works for me, thanks!
diff --git a/python/qemu/aqmp/legacy.py b/python/qemu/aqmp/legacy.py index 0890f95b16..6baa5f3409 100644 --- a/python/qemu/aqmp/legacy.py +++ b/python/qemu/aqmp/legacy.py @@ -56,6 +56,9 @@ def __init__(self, address: SocketAddrT, self._address = address self._timeout: Optional[float] = None + if server: + self._aqmp._bind_hack(address) # pylint: disable=protected-access + _T = TypeVar('_T') def _sync( diff --git a/python/qemu/aqmp/protocol.py b/python/qemu/aqmp/protocol.py index 50e973c2f2..33358f5cd7 100644 --- a/python/qemu/aqmp/protocol.py +++ b/python/qemu/aqmp/protocol.py @@ -15,6 +15,7 @@ from enum import Enum from functools import wraps import logging +import socket from ssl import SSLContext from typing import ( Any, @@ -238,6 +239,9 @@ def __init__(self, name: Optional[str] = None) -> None: self._runstate = Runstate.IDLE self._runstate_changed: Optional[asyncio.Event] = None + # Workaround for bind() + self._sock: Optional[socket.socket] = None + def __repr__(self) -> str: cls_name = type(self).__name__ tokens = [] @@ -427,6 +431,34 @@ async def _establish_connection( else: await self._do_connect(address, ssl) + def _bind_hack(self, address: Union[str, Tuple[str, int]]) -> None: + """ + Used to create a socket in advance of accept(). + + This is a workaround to ensure that we can guarantee timing of + precisely when a socket exists to avoid a connection attempt + bouncing off of nothing. + + Python 3.7+ adds a feature to separate the server creation and + listening phases instead, and should be used instead of this + hack. + """ + if isinstance(address, tuple): + family = socket.AF_INET + else: + family = socket.AF_UNIX + + sock = socket.socket(family, socket.SOCK_STREAM) + sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) + + try: + sock.bind(address) + except: + sock.close() + raise + + self._sock = sock + @upper_half async def _do_accept(self, address: SocketAddrT, ssl: Optional[SSLContext] = None) -> None: @@ -464,24 +496,27 @@ async def _client_connected_cb(reader: asyncio.StreamReader, if isinstance(address, tuple): coro = asyncio.start_server( _client_connected_cb, - host=address[0], - port=address[1], + host=None if self._sock else address[0], + port=None if self._sock else address[1], ssl=ssl, backlog=1, limit=self._limit, + sock=self._sock, ) else: coro = asyncio.start_unix_server( _client_connected_cb, - path=address, + path=None if self._sock else address, ssl=ssl, backlog=1, limit=self._limit, + sock=self._sock, ) server = await coro # Starts listening await connected.wait() # Waits for the callback to fire (and finish) assert server is None + self._sock = None self.logger.debug("Connection accepted.")
The synchronous QMP library would bind to the server address during __init__(). The new library delays this to the accept() call, because binding occurs inside of the call to start_[unix_]server(), which is an async method -- so it cannot happen during __init__ anymore. Python 3.7+ adds the ability to create the server (and thus the bind() call) and begin the active listening in separate steps, but we don't have that functionality in 3.6, our current minimum. Therefore ... Add a temporary workaround that allows the synchronous version of the client to bind the socket in advance, guaranteeing that there will be a UNIX socket in the filesystem ready for the QEMU client to connect to without a race condition. (Yes, it's a bit ugly. Fixing it more nicely will have to wait until our minimum Python version is 3.7+.) Signed-off-by: John Snow <jsnow@redhat.com> --- python/qemu/aqmp/legacy.py | 3 +++ python/qemu/aqmp/protocol.py | 41 +++++++++++++++++++++++++++++++++--- 2 files changed, 41 insertions(+), 3 deletions(-)