Specifications

D
evice Driver Programming
Glossary-8
module
A STREAMS module consists of two related queue structures, one each for upstream
and downstream messages. One or more modules may be pushed onto a stream between
the stream head and the driver, usually to implement and isolate a line discipline or a com-
munication protocol. virtual to physical memory.
outstanding asynchronous I/O request
A request that has not yet completed or a request that has completed but whose corre-
sponding control block has not yet been returned to the caller via a call to aiopoll(),
aiocancel(), or as an argument to a notification handler.
panic
The state where an unrecoverable error has occurred. Usually, when a panic occurs, a
message is displayed on the console to indicate the cause of the problem.
PDU
Protocol Data Unit
PowerPC 604
TM
The third implementation of the PowerPC family of microprocessors currently under
development. PowerPC 604 is used by Motorola Inc. under license by IBM.
prefix
A character name that uniquely identifies a driver's routines to the kernel. The prefix name
starts each routine in a driver. For example, a RAM disk might be given the ramd prefix.
If it is a block driver, the routines are ramdopen, ramdclose, ramdsize, ramd-
strategy, and ramdprint.
priority message
STREAMS messages that must move through the stream quickly are classified as priority
messages. They are placed at the head of the queue for processing by the srv(D2) rou-
tine.
queue
A data structure, the central node of a collection of structures and routines, which makes
up half of a STREAMS module or driver. Each module or driver is made up of one queue
each for upstream and downstream messages. Location: stream.h.
random I/O
I/O operations to the same file that specify absolute file offsets.