python/console_socket: accept existing FD in initializer

Useful if we want to use ConsoleSocket() for a socket created by
socketpair().

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Ani Sinha <anisinha@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20230928044943.849073-4-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/qemu/machine/console_socket.py

@@ -24,19 +24,32 @@ class ConsoleSocket(socket.socket):
     """
     ConsoleSocket represents a socket attached to a char device.
 
-    Optionally (if drain==True), drains the socket and places the bytes
-    into an in memory buffer for later processing.
-
-    Optionally a file path can be passed in and we will also
-    dump the characters to this file for debugging purposes.
+    :param address: An AF_UNIX path or address.
+    :param sock_fd: Optionally, an existing socket file descriptor.
+                    One of address or sock_fd must be specified.
+    :param file: Optionally, a filename to log to.
+    :param drain: Optionally, drains the socket and places the bytes
+                  into an in memory buffer for later processing.
     """
-    def __init__(self, address: str, file: Optional[str] = None,
+    def __init__(self,
+                 address: Optional[str] = None,
+                 sock_fd: Optional[int] = None,
+                 file: Optional[str] = None,
                  drain: bool = False):
+        if address is None and sock_fd is None:
+            raise ValueError("one of 'address' or 'sock_fd' must be specified")
+        if address is not None and sock_fd is not None:
+            raise ValueError("can't specify both 'address' and 'sock_fd'")
+
         self._recv_timeout_sec = 300.0
         self._sleep_time = 0.5
         self._buffer: Deque[int] = deque()
-        socket.socket.__init__(self, socket.AF_UNIX, socket.SOCK_STREAM)
-        self.connect(address)
+        if address is not None:
+            socket.socket.__init__(self, socket.AF_UNIX, socket.SOCK_STREAM)
+            self.connect(address)
+        else:
+            assert sock_fd is not None
+            socket.socket.__init__(self, fileno=sock_fd)
         self._logfile = None
         if file:
             # pylint: disable=consider-using-with