python/qmp: add send_fd_scm directly to QEMUMonitorProtocol

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 <[email protected]>
Reviewed-by: Hanna Reitz <[email protected]>
Reviewed-by: Paolo Bonzini <[email protected]>
Message-id: 20210923004938.3999963[email protected]
Signed-off-by: John Snow <[email protected]>

diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index ae945ca3c945f02af390902543a2a3eae234871b..1c6532a3d68726a1e3f65d66b8bdc4aea1daecb5 100644 (file)
--- a/python/qemu/machine/machine.py
+++ b/python/qemu/machine/machine.py
@@ -213,48 +213,22 @@ class QEMUMachine:
     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))
-
-        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)
+            self._qmp.send_fd_scm(fd)
 
-        return proc.returncode
+        return 0
 
     @staticmethod
     def _remove_if_exists(path: str) -> None:

diff --git a/python/qemu/qmp/__init__.py b/python/qemu/qmp/__init__.py
index c27594b66a2d70afbd7fe62545cb863fd2dbfe50..358c0971d06a02dd51b0f13ca8a77e91cc9557f4 100644 (file)
--- a/python/qemu/qmp/__init__.py
+++ b/python/qemu/qmp/__init__.py
@@ -21,6 +21,7 @@ import errno
 import json
 import logging
 import socket
+import struct
 from types import TracebackType
 from typing import (
     Any,
@@ -408,18 +409,14 @@ class QEMUMonitorProtocol:
             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.
-
-        @return The file descriptor number.
-        """
-        return self.__sock.fileno()
-
-    def is_scm_available(self) -> bool:
+        Send a file descriptor to the remote via SCM_RIGHTS.
         """
-        Check if the socket allows for SCM_RIGHTS.
+        if self.__sock.family != socket.AF_UNIX:
+            raise RuntimeError("Can't use SCM_RIGHTS on non-AF_UNIX socket.")
 
-        @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))]
+        )