fp_ioctl Kernel Service for Data Link Control (DLC) Devices

Purpose

Transfers special commands from the kernel to generic data link control (GDLC) using a file pointer.

Syntax

#include <sys/gdlextcb.h>
#include <fcntl.h>

int fp_ioctl (fp, cmd, arg, ext)

Parameters

Item	Description
fp	Specifies the file pointer of the target GDLC.
cmd	Specifies the operation to be performed by GDLC.
arg	Specifies the address of the parameter block. The argument for this parameter must be in the kernel space.
ext	Specifies the extension parameter. This parameter is ignored by GDLC.

Description

Various GDLC functions can be initiated using the fp_ioctl kernel service, such as changing configuration parameters, contacting the remote, and testing a link. Most of these operations can be completed before returning to the user synchronously. Some operations take longer, so asynchronous results are returned much later using the exception function handler. GDLC calls the kernel user's exception handler to complete these results. Each GDLC supports the fp_ioctl kernel service by way of its dlcioctl entry point. The fp_ioctl kernel service may be called from the process environment only.

Note: The DLC_GET_EXCEP ioctl operation is not used since all exception conditions are passed to the kernel user through the exception handler.

Return Values

Item	Description
0	Indicates a successful completion.
ENXIO	Indicates an invalid file pointer.
EINVAL	Indicates an invalid value.
ENOMEM	Indicates insufficient resources to satisfy the ioctl subroutine.

These return values are defined in the /usr/include/sys/errno.h file.