Glossary

anchor: A STREAMS locking mechanism that prevents the removal of STREAMS modules with the I_POP ioctl. Anchors are placed on STREAMS modules by adding the [anchor] flag to autopush configuration files or by directly calling the I_ANCHOR ioctl.
autopush: A STREAMS mechanism that enables a prespecified list of modules to be pushed automatically onto the stream when a STREAMS device is opened. This mechanism is used only for administrative purposes.
back-enable: To enable (by STREAMS) a preceding blocked queue's service procedure when STREAMS determines that a succeeding queue has reached its low-water mark.
blocked: A queue's service procedure that cannot be enabled due to flow control.
clone device: A STREAMS device that returns an unused major/minor device when initially opened, rather than requiring the minor device to be specified by name in the open call.
close routine: A procedure that is called when a module is popped from a stream or when a driver is closed.
controlling stream: A stream above the multiplexing driver used to establish the lower connections. Multiplexed stream configurations are maintained through the controlling stream to a multiplexing driver.
DDI: Device Driver Interface. An interface that facilitates driver portability across different UNIX system versions.
device driver: A stream component whose principle functions are handling an associated physical device and transforming data and information between the external interface and stream.
DKI: Driver-Kernel Interface. An interface between the UNIX system kernel and different types of drivers. It consists of a set of driver-defined functions that are called by the kernel. These functions are entry points into a driver.
downstream: A direction of data flow going from the stream head toward a driver. Also called write side and output side.
driver: A module that forms the stream end. It can be a device driver or a pseudo-device driver. It is a required component in STREAMS (except in STREAMS-based pipe mechanism), and physically identical to a module. It typically handles data transfer between the kernel and a device and does little or no processing of data.
enable: A term used to describe scheduling of a queue's service procedure.
FIFO: First in, first out. A term used in STREAMS for named pipes. This term is also used in queue scheduling.
flow control: A STREAMS mechanism that regulates the rate of message transfer within a stream and from user space into a stream.
hardware emulation module: A module required when the terminal line discipline is on a stream but there is no terminal driver at the end of the stream. This module recognizes all ioctls necessary to support terminal semantics specified by termio and termios.
input side: A direction of data flow going from a driver toward the stream head. Also called read side and upstream.
line discipline: A STREAMS module that performs termio canonical and non-canonical processing. It shares some termio processing with a driver in a STREAMS terminal subsystem.
lower stream: A stream connected below a multiplexer pseudo-device driver, by means of an I_LINK or I_PLINK ioctl. The far end of a lower stream terminates at a device driver or another multiplexer driver.
master driver: A STREAMS-based device supported by the pseudo-terminal subsystem. It is the controlling part of the pseudo-terminal subsystem (also called ptm).
message: One or more linked message blocks. A message is referenced by its first message block and its type is defined by the message type of that block.
message block: A triplet consisting of a data buffer and associated control structures, an msgb structure and a datab structure. It carries data or information, as identified by its message type, in a stream.
message queue: A linked list of zero or more messages connected together.
message type: A defined set of values identifying the contents of a message.


	Glossary anchor A STREAMS locking mechanism that prevents the removal of STREAMS modules with the `I_POP` `ioctl`. Anchors are placed on STREAMS modules by adding the `[anchor]` flag to `autopush` configuration files or by directly calling the `I_ANCHOR` `ioctl`. autopush A STREAMS mechanism that enables a prespecified list of modules to be pushed automatically onto the stream when a STREAMS device is opened. This mechanism is used only for administrative purposes. back-enable To enable (by STREAMS) a preceding blocked queue's service procedure when STREAMS determines that a succeeding queue has reached its low-water mark. blocked A queue's service procedure that cannot be enabled due to flow control. clone device A STREAMS device that returns an unused major/minor device when initially opened, rather than requiring the minor device to be specified by name in the open call. close routine A procedure that is called when a module is popped from a stream or when a driver is closed. controlling stream A stream above the multiplexing driver used to establish the lower connections. Multiplexed stream configurations are maintained through the controlling stream to a multiplexing driver. DDI Device Driver Interface. An interface that facilitates driver portability across different UNIX system versions. device driver A stream component whose principle functions are handling an associated physical device and transforming data and information between the external interface and stream. DKI Driver-Kernel Interface. An interface between the UNIX system kernel and different types of drivers. It consists of a set of driver-defined functions that are called by the kernel. These functions are entry points into a driver. downstream A direction of data flow going from the stream head toward a driver. Also called write side and output side. driver A module that forms the stream end. It can be a device driver or a pseudo-device driver. It is a required component in STREAMS (except in STREAMS-based pipe mechanism), and physically identical to a module. It typically handles data transfer between the kernel and a device and does little or no processing of data. enable A term used to describe scheduling of a queue's service procedure. FIFO First in, first out. A term used in STREAMS for named pipes. This term is also used in queue scheduling. flow control A STREAMS mechanism that regulates the rate of message transfer within a stream and from user space into a stream. hardware emulation module A module required when the terminal line discipline is on a stream but there is no terminal driver at the end of the stream. This module recognizes all `ioctl`s necessary to support terminal semantics specified by `termio` and `termios`. input side A direction of data flow going from a driver toward the stream head. Also called read side and upstream. line discipline A STREAMS module that performs `termio` canonical and non-canonical processing. It shares some `termio` processing with a driver in a STREAMS terminal subsystem. lower stream A stream connected below a multiplexer pseudo-device driver, by means of an `I_LINK` or `I_PLINK` `ioctl`. The far end of a lower stream terminates at a device driver or another multiplexer driver. master driver A STREAMS-based device supported by the pseudo-terminal subsystem. It is the controlling part of the pseudo-terminal subsystem (also called `ptm`). message One or more linked message blocks. A message is referenced by its first message block and its type is defined by the message type of that block. message block A triplet consisting of a data buffer and associated control structures, an `msgb` structure and a `datab` structure. It carries data or information, as identified by its message type, in a stream. message queue A linked list of zero or more messages connected together. message type A defined set of values identifying the contents of a message.