virtio: console: Ignore port name update request if name already set

We don't allow port name changes dynamically for a port.  So any
requests by the host to change the name are ignored.

Before this patch, if the hypervisor sent a port name while we had one
set already, we would leak memory equivalent to the size of the old
name.

This scenario wasn't expected so far, but with the suspend-resume
support, we'll send the VIRTIO_CONSOLE_PORT_READY message after restore,
which can get us into this situation.
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/virtio_console.c

@@ -1393,6 +1393,13 @@ static void handle_control_message(struct ports_device *portdev,
 		send_sigio_to_port(port);
 		break;
 	case VIRTIO_CONSOLE_PORT_NAME:
+		/*
+		 * If we woke up after hibernation, we can get this
+		 * again.  Skip it in that case.
+		 */
+		if (port->name)
+			break;
+
 		/*
 		 * Skip the size of the header and the cpkt to get the size
 		 * of the name that was sent