And the dbus log out as follow when `dbus-debug` t:
$ mkdir -p tmp/b.iso/ && cd tmp/ && touch a b.iso/c
$ emacs --batch --eval "(let ((dbus-debug t)) (message \"%s\" (expand-file-name \"a.iso/b\" \"/\")))"
xd_add_watch: fd 9, write 2, enabled 0
xd_add_watch: fd 9, write 0, enabled 1
Fdbus__init_bus: Bus :system, Reference counter 2
Fdbus_message_internal: DBUS_MESSAGE_TYPE_METHOD_CALL :system org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus AddMatch dbus-call-method-handler
Fdbus_message_internal: Parameter3 type='signal',interface='org.freedesktop.DBus.Local',member='Disconnected',path='/org/freedesktop/DBus/Local'
xd_signature: s
xd_append_arg: s type='signal',interface='org.freedesktop.DBus.Local',member='Disconnected',path='/org/freedesktop/DBus/Local'
Fdbus_message_internal: Message sent: (:serial :system 2)
xd_retrieve_arg: s :1.14469
xd_read_message_1: Event received: DBUS_MESSAGE_TYPE_SIGNAL 2 org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus NameAcquired (:1.14469)
xd_read_message_1: Event received: DBUS_MESSAGE_TYPE_METHOD_RETURN 2 org.freedesktop.DBus (null) (null) (null) nil
xd_read_message_1: Event stored: (:system 2 2 org.freedesktop.DBus nil nil nil dbus-call-method-handler)
DBus-Event (dbus-event :system 2 2 org.freedesktop.DBus nil nil nil dbus-call-method-handler)
DBus-Event (dbus-event :system 2 2 org.freedesktop.DBus nil nil nil dbus-call-method-handler)
DBus-Event (dbus-event :system 2 2 org.freedesktop.DBus nil nil nil dbus-call-method-handler)
Matching rule "type='signal',interface='org.freedesktop.DBus.Local',member='Disconnected',path='/org/freedesktop/DBus/Local'" created
D-Bus error: "No connection to bus", :session