The Solaris DDI/DKI divides the software interface to SCSI devices into two major parts: target drivers and host bus adapter (HBA) drivers. Target refers to a driver for a device on a SCSI bus, such as a disk or a tape drive. host bus adapter refers to the driver for the SCSI controller on the host machine, such as the "esp" driver on a SPARCstation. SCSA defines the interface between these two components. This chapter discusses target drivers only. See Chapter 14, SCSI Host Bus Adapter Drivers for information on host bus adapter drivers.
The terms "host bus adapter" or "HBA" used in this manual are equivalent to the phrase "host adapter" defined in SCSI specifications.
Target drivers can be either character or block device drivers, depending on the device. Drivers for tape drives are usually character device drivers, while disks are handled by block device drivers. This chapter describes how to write a SCSI target driver and discusses the additional requirements that SCSA places on block and character drivers for SCSI target devices.