Because SCSI devices are not self-identifying, a hardware configuration file is required for a target driver (see driver.conf(4) and scsi(4) for details). A typical configuration file looks like this:
name="xx" class="scsi" target=2 lun=0;
The system reads the file during autoconfiguration and uses the class property to identify the driver's possible parent. The system then attempts to attach the driver to any parent driver that is of class scsi. All host bus adapter drivers are of this class. Using the class property rather than the parent property enables the target driver to be attached to any host bus adapter driver that finds the expected device at the specified target and lun ids. The target driver is responsible for verifying this in its probe(9E) routine.