[PATCH 1/4] python: stop using socket_scm_helper

[Paolo Bonzini <pbonzini@redhat.com>]

Python is able to call sendmsg, it does not need a helper.  Write the
code directly; for now, keep the weird calling convention.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 python/qemu/machine/machine.py | 48 ++++++++++++----------------------
 python/qemu/qmp/__init__.py    | 15 +++++++++++
 2 files changed, 32 insertions(+), 31 deletions(-)

diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index 34131884a5..e4356ea99e 100644
--- a/python/qemu/machine/machine.py
+++ b/python/qemu/machine/machine.py
@@ -213,48 +213,34 @@ 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 via QMP.
 
         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.
+        If it is file_path, the function will open that file and pass
+        its own fd.
         """
         # 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)
+            fd = -1
+            try:
+                fd = os.open(file_path, os.O_RDONLY)
+                self._qmp.send_fd(fd)
+            except OSError:
+                return 1
+            finally:
+                if fd != -1:
+                    os.close(fd)
         else:
             assert fd is not None
-            fd_param.append(str(fd))
+            try:
+                self._qmp.send_fd(fd)
+            except OSError:
+                return 1
 
-        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:
diff --git a/python/qemu/qmp/__init__.py b/python/qemu/qmp/__init__.py
index 269516a79b..27a3e8f7af 100644
--- a/python/qemu/qmp/__init__.py
+++ b/python/qemu/qmp/__init__.py
@@ -17,6 +17,7 @@
 # This work is licensed under the terms of the GNU GPL, version 2.  See
 # the COPYING file in the top-level directory.
 
+import array
 import errno
 import json
 import logging
@@ -421,3 +422,17 @@ def is_scm_available(self) -> bool:
         @return True if SCM_RIGHTS is available, otherwise False.
         """
         return self.__sock.family == socket.AF_UNIX
+
+    def send_fd(self, fd: int) -> None:
+        """
+        Send a file descriptor to QEMU via SCM_RIGHTS.
+
+        @param fd (int): file descriptor do be sent
+
+        @raise OSError: if the sendmsg system call fails.
+        """
+        # Send a single space so that QEMU looks at the ancillary data
+        self.__sock.sendmsg((b" ", ),
+                            [(socket.SOL_SOCKET,
+                              socket.SCM_RIGHTS,
+                              array.array("i", [fd]).tobytes())])
-- 
2.31.1