Device Instances and Instance Numbers

The system assigns an instance number to each device. The driver may not reliably predict the value of the instance number assigned to a particular device. The driver should retrieve the particular instance number that has been assigned by calling ddi_get_instance(9F).

Instance numbers represent the system's notion of devices. Each dev_info (that is, each node in the device tree) for a particular driver is assigned an instance number by the kernel. Furthermore, instance numbers provide a convenient mechanism for indexing data specific to a particular physical device. The most common usage for this is ddi_get_soft_state(9F) which uses an instance number to retrieve soft state data for a particular physical device.