The Fibre Channel Protocol for SCSI (FCP) subsystem has two parts:
The adapter device driver is designed to shield you from having to communicate directly with the system I/O hardware. This gives you the ability to successfully write a device driver without having a detailed knowledge of the system hardware. You can look at the subsystem as a two-tiered structure in which the adapter device driver is the bottom or supporting layer. As a programmer, you need only worry about the upper layer. This chapter only discusses writing a device driver, because the adapter device driver is already provided.
The adapter device driver, or lower layer, is responsible only for the communications to and from the bus, and any error logging and recovery. The upper layer is responsible for all of the device-specific commands. The device driver should handle all commands directed towards its specific device by building the necessary sequence of I/O requests to the adapter device driver in order to properly communicate with the device.
These I/O requests contain the commands that are needed by the device. One important aspect to note is that the device driver cannot access any of the adapter resources and should never try to pass the commands directly to the adapter, since it has absolutely no knowledge of the meaning of those commands.
For more information on Physical Volume Identifiers (PVID), see Making an Available Disk a Physical Volume in AIX 5L Version 5.2 System Management Guide: Operating System and Devices.