File and device input/output

STREAMS system calls

The STREAMS-related system calls are as follows:

open: Open a Stream
close: Close a Stream
read: Read data from a Stream
write: Write data to a Stream
ioctl: Control a Stream
getmsg: Receive a message at the Stream head
putmsg: Send a message downstream
poll: Notify the application program when selected events occur on a Stream
pipe: Create a channel that provides a communication path between multiple processes

A STREAMS device responds to the standard character I/O system calls, such as read and write, by turning the request into a message. This feature ensures that STREAMS devices may be accessed from the user level in the same manner as non-STREAMS character devices. However, additional system calls provide other capabilities.

getmsg and putmsg

The putmsg and getmsg system calls enable a user process to send and receive STREAMS messages, in the same form the messages have in kernel modules and drivers. read and write are not designed to include the message boundaries necessary to encode messages.

The advantage of this capability is that a user process, as well as a STREAMS module or driver, can implement a service interface.

poll

The poll system call allows a user process to monitor a number of streams to detect expected I/O events. Such events might be the availability of a device for writing, input data arriving from a device, a hangup occurring, an error being detected, or the arrival of a priority message. See poll(2) for more information.