ddselect Communications PDH Entry Point

Purpose

Checks to see whether a specified event or events has occurred on the device.

Syntax

#include <sys/device.h>
#include <sys/comio.h>

int ddselect (devno, events, reventp, chan) dev_t devno; ushort events; ushort * reventp; int chan;

Parameters

Item	Description
devno	Specifies major and minor device numbers.
events	Specifies conditions to check. The conditions are denoted by the bitwise OR of one or more of the following: POLLIN Check whether receive data is available. POLLOUT Check whether transmit available. POLLPRI Check whether status is available. POLLSYNC Check whether asynchronous notification is available.
reventp	Points to the result of condition checks. A bitwise OR of the following conditions is returned: POLLIN Indicates receive data is available. POLLOUT Indicates transmit available. POLLPRI Indicates status is available.
chan	Specifies the channel number assigned by the device handler's ddmpx entry point.

Description

Note: This entry point should not be called by a kernel-mode process.

The ddselect communications PDH entry point checks and returns the status of 1 or more conditions for a user-mode process. It works the same way the common ddselect device driver entry point does.

Execution Environment

A ddselect entry point can be called from the process environment only.

Return Values

In general, communication device handlers use the common return codes defined for an entry point. However, device handlers for specific communication devices may return device-specific codes. The common return codes for the ddselect entry point are the following:

Return Code	Description
ENXIO	Indicates an attempt to use an unconfigured device.
EINVAL	Indicates a specified argument is not valid.
EACCES	Indicates a call from a kernel process is not valid.
EBUSY	Indicates the maximum number of opens was exceeded.
ENODEV	Indicates the device does not exist.