Overview of Host Adapter Driver Architecture

Overview of Host Adapter Driver Architecture

A host adapter driver is a low-level driver for a SCSI bus adapter. A host adapter driver is similar to other device drivers described in this book in many ways:

Like other device drivers, it uses the kernel facilities described in Chapter 9, "Device Driver/Kernel Interface."
It is compiled and linked like other drivers (see Chapter 10, "Building and Installing a Driver.").
It is configured to the system using files in /var/sysgen/master.d, and loaded by lboot. A host adapter driver should not be loadable; if it is loadable, it should not unload.
Like other drivers, it can have entry points pfxstart() or pfxedtinit() for initialization, pfxintr() for interrupt handling, and pfxhalt() for shutdown.

Unlike other drivers, a host adapter driver does not provide any entry points for serving the needs of system functions, such as pfxread(), pfxpoll(), or pfxstrategy(). Instead, it supplies the entry points used by SCSI device drivers.