+ *
+ * pci_fill_info() returns the current value of pci_dev->known_fields.
+ * This is a bit mask of all fields, which were already obtained during
+ * the lifetime of the device. This includes fields which are not supported
+ * by the particular device -- in that case, the field is left at its default
+ * value, which is 0 for integer fields and NULL for pointers. On the other
+ * hand, we never consider known fields unsupported by the current back-end;
+ * such fields always contain the default value.
+ *
+ * XXX: flags and the result should be unsigned, but we do not want to break the ABI.