HP OpenVMS I/O User’s Reference Manual: OpenVMS Version 8.4
Table of Contents
An ancillary control process (ACP) is a process that interfaces between the user process and the driver, and performs functions that supplement the driver's functions. Virtual I/O operations involving file-structured devices (disks and magnetic tapes) often require ACP intervention. In most cases, ACP intervention is requested by OpenVMS Record Management Services (RMS) and is transparent to the user process; however, user processes can request ACP functions directly by issuing a Queue I/O (QIO) request and specifying an ACP function code.
Executing physical and logical input/output (I/O) operations on a device that is managed by a file ACP interferes with the operation of the ACP, and can result in unpredictable consequences such as system failure.
In addition to the ACP, the XQP (extended QIO processor) facility supplements the QIO driver's functions when performing virtual I/O operations on file-structured devices; however, rather than being a separate process, the XQP executes as a kernel-mode thread in the process of its caller.
This chapter describes the QIO interface to ACPs for disk and magnetic tape devices (file system ACPs). The sample program in Chapter 10 performs QIO operations to the magnetic tape ACP.
Programs written in BLISS-32 can use these symbols by referencing them and including the correct library, SYS$LIBRARY:STARLET.L32 (for the macros listed under SYS$LIBRARY:STARLET.MLB), and SYS$LIBRARY:LIB.L32 (for the macros listed under SYS$LIBRARY:LIB.MLB).