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.\"     $OpenBSD: ioctl.2,v 1.11 2001/07/30 01:12:43 deraadt Exp $

.\"     $NetBSD: ioctl.2,v 1.5 1995/02/27 12:33:47 cgd Exp $

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.\"     @(#)ioctl.2     8.2 (Berkeley) 12/11/93

.\"

.Dd December 11, 1993

.Dt IOCTL 2

.Os

.Sh NAME

.Nm ioctl

.Nd control device

.Sh SYNOPSIS

.Fd #include 

.Ft int

.Fn ioctl "int d" "unsigned long request" "..."

.Sh DESCRIPTION

The

.Fn ioctl

function manipulates the underlying device parameters of special files.

In particular, many operating

characteristics of character special files (e.g., terminals)

may be controlled with

.Fn ioctl

requests.

.Pp

The argument

.Fa d

must be an open file descriptor. The third argument is called

.Fa arg

and contains additional information needed by this device

to perform the requested function.

.Fa arg

is either an

.Li int

or a pointer to a device-specific data structure, depending upon

the given

.Fa request .

.Pp

An

.Nm

.Fa request

has encoded in it whether the argument is an

.Dq in

parameter

or

.Dq out

parameter, and the size of the third argument

.Pq Fa arg

in bytes.

Macros and defines used in specifying an ioctl

.Fa request

are located in the file

.Ao Pa sys/ioctl.h Ac .

.Sh RETURN VALUES

If an error has occurred, a value of \-1 is returned and

.Va errno

is set to indicate the error.

.Sh ERRORS

.Fn ioctl

will fail if:

.Bl -tag -width Er

.It Bq Er EBADF

.Fa d

is not a valid descriptor.

.It Bq Er ENOTTY

.Fa d

is not associated with a character

special device.

.It Bq Er ENOTTY

The specified request does not apply to the kind

of object that the descriptor

.Fa d

references.

.It Bq Er EINVAL

.Fa request

or

.Fa arg

is not valid.

.It Bq Er EFAULT

.Fa arg

points outside the process's allocated address space.

.El

.Sh SEE ALSO

.Xr cdio 1 ,

.Xr chio 1 ,

.Xr mt 1 ,

.Xr execve 2 ,

.Xr fcntl 2 ,

.Xr intro 4 ,

.Xr tty 4

.Sh HISTORY

An

.Fn ioctl

function call appeared in

.At v7 .