1.\" $OpenBSD: ioctl.2,v 1.20 2022/09/11 06:38:11 jmc Exp $ 2.\" $NetBSD: ioctl.2,v 1.5 1995/02/27 12:33:47 cgd Exp $ 3.\" 4.\" Copyright (c) 1980, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)ioctl.2 8.2 (Berkeley) 12/11/93 32.\" 33.Dd $Mdocdate: September 11 2022 $ 34.Dt IOCTL 2 35.Os 36.Sh NAME 37.Nm ioctl 38.Nd control device 39.Sh SYNOPSIS 40.In sys/ioctl.h 41.Ft int 42.Fn ioctl "int d" "unsigned long request" "..." 43.Sh DESCRIPTION 44The 45.Fn ioctl 46function manipulates the underlying device parameters of special files. 47In particular, many operating 48characteristics of character special files (e.g., terminals) 49may be controlled with 50.Fn ioctl 51requests. 52.Pp 53The argument 54.Fa d 55must be an open file descriptor. 56The third argument is called 57.Fa arg 58and contains additional information needed by this device 59to perform the requested function. 60.Fa arg 61is either an 62.Vt int 63or a pointer to a device-specific data structure, depending upon 64the given 65.Fa request . 66.Pp 67An 68.Nm 69.Fa request 70has encoded in it whether the argument is an 71.Dq in 72parameter 73or 74.Dq out 75parameter, and the size of the third argument 76.Pq Fa arg 77in bytes. 78Macros and defines used in specifying an ioctl 79.Fa request 80are located in the file 81.In sys/ioctl.h . 82.Sh GENERIC IOCTLS 83Some ioctls are applicable to any file descriptor. 84These include: 85.Bl -tag -width "xxxxxx" 86.It Dv FIOCLEX 87Set close-on-exec flag. 88The file will be closed when 89.Xr execve 2 90is invoked. 91.It Dv FIONCLEX 92Clear close-on-exec flag. 93The file will remain open across 94.Xr execve 2 . 95.El 96.Pp 97Some generic ioctls are not implemented for all types of file 98descriptors. 99These include: 100.Bl -tag -width "xxxxxx" 101.It Dv FIONREAD Fa "int *" 102Get the number of bytes that are immediately available for reading. 103.It Dv FIONBIO Fa "int *" 104Set non-blocking I/O mode if the argument is non-zero. 105In non-blocking mode, 106.Xr read 2 107or 108.Xr write 2 109calls return \-1 and set 110.Va errno 111to 112.Er EAGAIN 113immediately when no data is available. 114.It Dv FIOASYNC Fa "int *" 115Set asynchronous I/O mode if the argument is non-zero. 116In asynchronous mode, the process or process group specified by 117.Dv FIOSETOWN 118will start receiving 119.Dv SIGIO 120signals when data is available. 121The 122.Dv SIGIO 123signal will be delivered when data is available on the file 124descriptor. 125.It Dv FIOSETOWN, FIOGETOWN Fa "int *" 126Set/get the process or the process group (if negative) that should receive 127.Dv SIGIO 128signals when data is available. 129.El 130.Sh RETURN VALUES 131If an error has occurred, a value of \-1 is returned and 132.Va errno 133is set to indicate the error. 134.Sh ERRORS 135.Fn ioctl 136will fail if: 137.Bl -tag -width Er 138.It Bq Er EBADF 139.Fa d 140is not a valid descriptor. 141.It Bq Er ENOTTY 142.Fa d 143is not associated with a character 144special device. 145.It Bq Er ENOTTY 146The specified request does not apply to the kind 147of object that the descriptor 148.Fa d 149references. 150.It Bq Er EINVAL 151.Fa request 152or 153.Fa arg 154is not valid. 155.It Bq Er EFAULT 156.Fa arg 157points outside the process's allocated address space. 158.El 159.Sh SEE ALSO 160.Xr cdio 1 , 161.Xr chio 1 , 162.Xr mt 1 , 163.Xr execve 2 , 164.Xr fcntl 2 , 165.Xr intro 4 , 166.Xr tty 4 167.Sh HISTORY 168An 169.Fn ioctl 170function call appeared in 171.At v7 . 172