As described in Chapter 13, SCSI Target Drivers, the Solaris 7 DDI/DKI divides the software interface to SCSI devices into two major parts:
Target devices and drivers
Host bus adapter devices and drivers
Target device refers to a device on a SCSI bus, such as a disk or a tape drive. Target driver refers to a software component installed as a device driver. Each target device on a SCSI bus is controlled by one instance of the target driver.
Host bus adapter device refers to HBA hardware, such as an SBus or ISA SCSI adapter card. Host bus adapter driver refers to a software component installed as a device driver, such as the esp driver on a SPARCstation or the aha driver on an x86 machine. An instance of the HBA driver controls each of its host bus adapter devices configured in the system.
The terms "host bus adapter" or "HBA" used in this manual are equivalent to the phrase "host adapter" as defined in the SCSI standards.
The Sun Common SCSI Architecture (SCSA) defines the interface between these target and HBA components.
SCSA is the Solaris 7 DDI/DKI programming interface for the transmission of SCSI commands from a target driver to a host adapter driver. By conforming to the SCSA, the target driver can pass any combination of SCSI commands and sequences to a target device without knowledge of the hardware implementation of the host adapter. SCSA conceptually separates the building of a SCSI command (by the target driver) from the transporting of the command to and data to and from the SCSI bus (by the HBA driver) for the appropriate target device. SCSA manages the connections between the target and HBA drivers through an HBA transport layer, as shown in Figure 14-1.
The HBA transport layer is a software and hardware layer responsible for transporting a SCSI command to a SCSI target device. The HBA driver provides resource allocation, DMA management, and transport services in response to requests made by SCSI target drivers through SCSA. The host adapter driver also manages the host adapter hardware and the SCSI protocols necessary to perform the commands. When a command has been completed, the HBA driver calls the target driver's SCSI pkt command completion routine.
Figure 14-2 illustrates this flow, with emphasis placed on the transfer of information from target drivers to SCSA to HBA drivers. Typical transport entry points and function calls are included.