ioctl(2)

NAME

ioctl − control device

SYNOPSIS

int ioctl (fildes, request, arg)
int fildes, request;
char ∗arg;

DESCRIPTION

ioctl performs a variety of control functions on devices, sockets, and STREAMS. For non-STREAMS files, the functions performed by this call are device-specific control functions. The arguments request and arg are passed to the file designated by fildes and are interpreted by the device driver. This control is infrequently used on non-STREAMS devices, with the basic input/output functions performed through the read(2) and write(2) system calls.

For STREAMS files, specific functions are performed by the ioctl call as described in streamio(7).

For sockets, specific functions are performed by the ioctl call as described in intro(4N) and sockio(7).

Fildes is an open file descriptor that refers to a device. Request selects the control function to be performed and will depend on the device being addressed. Arg represents additional information that is needed by this specific device to perform the requested function. The data type of arg depends upon the particular control request, but it is either an integer or a pointer to a device-specific data structure.

In addition to device-specific and STREAMS functions, generic functions are provided by more than one device driver, for example, the general terminal interface [see termio(7)].

ioctl will fail for any type of file if one or more of the following are true:

[EACCES]
Future error.

[EBADF] Fildes is not a valid open file descriptor.

[ENOTTY] Fildes is not associated with a device driver that accepts control functions.

[EINTR] A signal was caught during the ioctl system call.

ioctl will also fail if the device driver detects an error. In this case, the error is passed through ioctl without change to the caller. A particular driver might not have all of the following error cases. Other requests to device drivers will fail if one or more of the following are true:

[EFAULT]
Request requires a data transfer to or from a buffer pointed to by arg, but some part of the buffer is outside the process’s allocated space.

[EINVAL] Request or arg is not valid for this device.

[EIO] Some physical I/O error has occurred.

[ENXIO] The request and arg are valid for this device driver, but the service requested can not be performed on this particular subdevice.

[ENOLINK] Fildes is on a remote machine and the link to that machine is no longer active.

[EPERM] Arg is valid, but the service requested cannot be performed, because of ownership, privilege, or job control restrictions.

STREAMS errors are described in streamio(7).

DIAGNOSTICS

Upon successful completion, the value returned depends upon the device control function, but must be a non-negative integer. Otherwise, a value of −1 is returned and errno is set to indicate the error.

NOTE

This call is defined in the 88open Binary and Object Compatibility Standards (BCS/OCS) as well as their respective 88open Networking Supplements (BCSNS/OCSNS) for use in BCS/OCS compliant applications. OCS/OCSNS-defined functions may be accessed by passing OCS options to cc(1) and ld(1).

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