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. Refer to the HP OpenVMS System Manager's Manual and
the HP OpenVMS System Management Utilities Reference Manual for information about installing images with privileges.
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. Refer to the OpenVMS Programming Concepts manual for information about creating
shareable images.