8.4 Accessing the OpenVMS Generic SCSI Class Driver

Interactive commands and procedure calls can use the OpenVMS generic SCSI class driver to access devices on the SCSI bus. However, it is unlikely that a user application would access a device on the SCSI bus by directly using the $QIO interface of the generic SCSI class driver. First of all, any user process directly using the $QIO interface would require DIAGNOSE and PHY_IO or LOG_IO privileges. Under normal circumstances, it would be a system security risk to grant DIAGNOSE and PHY_IO or LOG_IO privileges to many system users. Secondly, it would be cumbersome for end users of the device to identify, format, and issue SCSI commands to the device. Rather, it would be more efficient to develop an interface that hides these details.

A utility program, installed with the DIAGNOSE and PHY_IO or LOG_IO privileges, can provide nonprivileged users with a command-line interface to a SCSI device. The utility translates interactive commands provided by the user into the appropriate set of SCSI commands and sends them to the device using the $QIO interface provided by the generic SCSI class driver. The utility checks user commands to ensure that only valid SCSI commands are sent to the device. For information about installing images with privileges, see the HP OpenVMS System Manager's Manual and the HP OpenVMS System Management Utilities Reference Manual .

A privileged shareable image can provide system applications with a procedure interface to a SCSI device. The image contains a set of procedures that translate operations specified by the caller into the appropriate set of SCSI commands. The SCSI commands are sent to the device through the $QIO interface of the generic SCSI class driver. The privileged shareable image checks its caller's parameters to ensure that only valid SCSI commands are sent to the device. For information about creating shareable images, see the HP OpenVMS Programming Concepts manual.