+/*
+ * Some details of how volume and device reservations work
+ *
+ * class VOLRES:
+ * set_in_use() volume being used on current drive
+ * clear_in_use() no longer being used. Can be re-used or moved.
+ * set_swapping() set volume being moved to another drive
+ * is_swapping() volume is being moved to another drive
+ * clear_swapping() volume normal
+ *
+ * class DEVICE:
+ * set_load() set to load volume
+ * needs_load() volume must be loaded (i.e. set_load done)
+ * clear_load() load done.
+ * set_unload() set to unload volume
+ * needs_unload() volume must be unloaded
+ * clear_unload() volume unloaded
+ *
+ * reservations are temporary until the drive is acquired
+ * inc_reserved() increments num of reservations
+ * dec_reserved() decrements num of reservations
+ * num_reserved() number of reservations
+ *
+ * class DCR:
+ * set_reserved() sets local reserve flag and calls dev->inc_reserved()
+ * clear_reserved() clears local reserve flag and calls dev->dec_reserved()
+ * is_reserved() returns local reserved flag
+ * unreserve_device() much more complete unreservation
+ *
+ */
+