CIO_GET_FASTWRT ddioctl Communications PDH Operation

Purpose

Provides the parameters required to issue a kernel-mode fast-write call.

Syntax

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

int ddioctl (devno, op, parmptr, devflag, chan, ext) dev_t devno; int op; struct status_block * parmptr; ulong devflag; int chan, ext;

Description

The CIO_GET_FASTWRT operation returns the parameters required to issue a kernel-mode fast write for a particular device. Only a kernel-mode process can issue this entry point and use the fast-write function. The parameters returned are located in the cio_get_fastwrt structure in the /usr/include/sys/comio.h file.

Note: This operation should not be called by user-mode processes.

Parameters

Item	Description
devno	Specifies major and minor device numbers.
op	Indicates the entry point for the CIO_GET_FASTWRT operation.
parmptr	Points to a cio_get_fastwrt structure. This structure is defined in the /usr/include/sys/comio.h file.
devflag	Indicates the DKERNEL flag. This flag must be set, indicating a call by a kernel-mode process.
chan	Specifies the channel number assigned by the device-handler ddmpx entry point.
ext	Specifies the extended subroutine parameter. This parameter is device-dependent.

Execution Environment

A CIO_GET_FASTWRT operation can be called from the process environment only.

Return Values

In general, communication device handlers use the common codes defined for an operation. However, device handlers for specific communication devices may return device-specific codes. The common return codes for the CIO_GET_FASTWRT operation are:

Item	Description
ENXIO	Indicates an attempt to use an unconfigured device.
EFAULT	Indicates that the specified address is not valid.
EINVAL	Indicates a parameter call that is not valid.
EPERM	Indicates a call from a user-mode process is not valid.
EBUSY	Indicates the maximum number of opens was exceeded.
ENODEV	Indicates the device does not exist.