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python/qmp: add send_fd_scm directly to QEMUMonitorProtocol

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It turns out you can do this directly from Python ... and because of
this, you don't need to worry about setting the inheritability of the
fds or spawning another process.

Doing this is helpful because it allows QEMUMonitorProtocol to keep its
file descriptor and socket object as private implementation
details. /that/ is helpful in turn because it allows me to write a
compatible, alternative implementation.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20210923004938.3999963-10-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
This commit is contained in:
John Snow 2021-09-22 20:49:30 -04:00
parent d911accf0a
commit 514d00df5f
2 changed files with 19 additions and 48 deletions
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44
python/qemu/machine/machine.py
View file

@ -213,48 +213,22 @@ def add_fd(self: _T, fd: int, fdset: int,
def send_fd_scm(self, fd: Optional[int] = None,
file_path: Optional[str] = None) -> int:
"""
Send an fd or file_path to socket_scm_helper.
Send an fd or file_path to the remote via SCM_RIGHTS.
Exactly one of fd and file_path must be given.
If it is file_path, the helper will open that file and pass its own fd.
Exactly one of fd and file_path must be given. If it is
file_path, the file will be opened read-only and the new file
descriptor will be sent to the remote.
"""
# In iotest.py, the qmp should always use unix socket.
assert self._qmp.is_scm_available()
if self._socket_scm_helper is None:
raise QEMUMachineError("No path to socket_scm_helper set")
if not os.path.exists(self._socket_scm_helper):
raise QEMUMachineError("%s does not exist" %
self._socket_scm_helper)
# This did not exist before 3.4, but since then it is
# mandatory for our purpose
if hasattr(os, 'set_inheritable'):
os.set_inheritable(self._qmp.get_sock_fd(), True)
if fd is not None:
os.set_inheritable(fd, True)
fd_param = ["%s" % self._socket_scm_helper,
"%d" % self._qmp.get_sock_fd()]
if file_path is not None:
assert fd is None
fd_param.append(file_path)
with open(file_path, "rb") as passfile:
fd = passfile.fileno()
self._qmp.send_fd_scm(fd)
else:
assert fd is not None
fd_param.append(str(fd))
self._qmp.send_fd_scm(fd)
proc = subprocess.run(
fd_param,
stdin=subprocess.DEVNULL,
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT,
check=False,
close_fds=False,
)
if proc.stdout:
LOG.debug(proc.stdout)
return proc.returncode
return 0
@staticmethod
def _remove_if_exists(path: str) -> None:

23
python/qemu/qmp/__init__.py
View file

@ -21,6 +21,7 @@
import json
import logging
import socket
import struct
from types import TracebackType
from typing import (
Any,
@ -408,18 +409,14 @@ def settimeout(self, timeout: Optional[float]) -> None:
raise ValueError(msg)
self.__sock.settimeout(timeout)
def get_sock_fd(self) -> int:
def send_fd_scm(self, fd: int) -> None:
"""
Get the socket file descriptor.
Send a file descriptor to the remote via SCM_RIGHTS.
"""
if self.__sock.family != socket.AF_UNIX:
raise RuntimeError("Can't use SCM_RIGHTS on non-AF_UNIX socket.")
@return The file descriptor number.
"""
return self.__sock.fileno()
def is_scm_available(self) -> bool:
"""
Check if the socket allows for SCM_RIGHTS.
@return True if SCM_RIGHTS is available, otherwise False.
"""
return self.__sock.family == socket.AF_UNIX
self.__sock.sendmsg(
[b' '],
[(socket.SOL_SOCKET, socket.SCM_RIGHTS, struct.pack('@i', fd))]
)