HDK Technical Reference

SDI pass-through interface

The SDI pass-through interface gives a user program direct access to a device. By permitting user programs to act in a manner similar to a target driver, the overhead of instructions needed to make device-specific requests can be removed from a target driver. An example of device-specific requests are the instructions required to format a disk. With the pass-through interface, a user program can select different instruction packages for different vendors' drives. Not only can many instructions be removed from a driver, but a driver can be made to work on a wider range of different devices. In addition, a driver need not be updated as frequently when a device changes.

The pass-through interface gives you a means of evaluating new peripherals and controllers without developing a driver, checking device states, and eliminates duplication of driver code.

Two pass-through interface schemes are available:

pass-through library interface
The pass-through library interface, implemented through the /dev/passthru0 device and the ( library, provides routines that applications can use to issue device-specific requests. It supports extended SCSI addressing and is not available on systems prior to UnixWare 7 Release 7.1. See ``Using the pass-through library interface''.

pass-through ioctl interface
Uses pre-defined ioctl requests to issue device-specific requests. This was the only pass-through interface on pre-Release 7.1 systems, and is supported for compatibility with earlier systems and existing drivers. Applications written for Release 7.1 should use the pass-through library interface. The ioctl interface does not support extended SCSI addressing. See ``Using the pass-through ioctl interface''.

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OpenServer 6 and UnixWare (SVR5) HDK - June 2005