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.