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.\" $OpenBSD: ioctl.2,v 1.19 2019/08/11 15:48:08 deraadt Exp $
.\" $NetBSD: ioctl.2,v 1.5 1995/02/27 12:33:47 cgd Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)ioctl.2 8.2 (Berkeley) 12/11/93
.\"
.Dd $Mdocdate: August 11 2019 $
.Dt IOCTL 2
.Os
.Sh NAME
.Nm ioctl
.Nd control device
.Sh SYNOPSIS
.In sys/ioctl.h
.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
.In sys/ioctl.h .
.Sh GENERIC IOCTLS
Some ioctls are applicable to any file descriptor.
These include:
.Bl -tag -width "xxxxxx"
.It Dv FIOCLEX
Set close-on-exec flag.
The file will be closed when
.Xr execve 2
is invoked.
.It Dv FIONCLEX
Clear close-on-exec flag.
The file will remain open across
.Xr execve 2 .
.El
.Pp
Some generic ioctls are not implemented for all types of file
descriptors.
These include:
.Bl -tag -width "xxxxxx"
.It Dv FIONREAD Fa "int *"
Get the number of bytes that are immediately available for reading.
.It Dv FIONBIO Fa "int *"
Set non-blocking I/O mode if the argument is non-zero.
In non-blocking mode,
.Xr read 2
or
.Xr write 2
calls return \-1 and set
.Va errno
to
.Er EAGAIN
immediately when no data is available.
.It Dv FIOASYNC Fa "int *"
Set asynchronous I/O mode if the argument is non-zero.
In asynchronous mode, the process or process group specified by
.Dv FIOSETOWN
will start receiving
.Dv SIGIO
signals when data is available.
The
.Dv SIGIO
signal will be delivered when data is available on the file
descriptor.
.It Dv FIOSETOWN, FIOGETOWN Fa "int *"
Set/get the process or the process group (if negative) that should receive
.Dv SIGIO
signals when data is available.
.El
.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 .
|
