1.\" $NetBSD: ioctl.9,v 1.26 2008/11/12 12:35:54 ad Exp $ 2.\" 3.\" Copyright (c) 1999 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Heiko W.Rupp <hwr@pilhuhn.de> 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd February 22, 2018 31.Dt IOCTL 9 32.Os 33.Sh NAME 34.Nm ioctl , 35.Nm _IO , 36.Nm _IOR , 37.Nm _IOW , 38.Nm _IOWR 39.Nd "how to implement a new ioctl call to access device drivers" 40.Sh SYNOPSIS 41.In sys/ioctl.h 42.In sys/ioccom.h 43.Ft int 44.Fn ioctl "int d" "unsigned long request" "..." 45.Fn _IO "g" "t" 46.Fn _IOR "g" "n" "t" 47.Fn _IOW "g" "n" "t" 48.Fn _IOWR "g" "n" "t" 49.Sh DESCRIPTION 50Whenever an 51.Xr ioctl 2 52call is made, the kernel dispatches it to the device driver 53which can then interpret the request number and data in a specialized 54manner. 55Ioctls are defined as: 56.Bd -literal 57#define MYDEVIOCTL fun(g, n, t) 58.Ed 59.Pp 60where the different symbols correspond to: 61.Bl -tag -width ".Dv MYDEVIOCTL" 62.It Dv MYDEVIOCTL 63The name which will later be given in the 64.Xr ioctl 2 65system call as second argument, e.g., 66.Bd -literal 67ioctl(fd, MYDEVIOCTL, ...) 68.Ed 69.It Fn fun 70A macro which can be one of: 71.Bl -tag -width ".Fn _IOWR" 72.It Fn _IO 73The call is a simple message to the kernel by itself. 74It does not copy anything into the kernel, nor does it want anything back. 75.It Fn _IOR 76The call only reads parameters from the kernel and does not 77pass any to it. 78.It Fn _IOW 79The call only writes parameters to the kernel, but does not want anything 80back. 81.It Fn _IOWR 82The call writes data to the kernel and wants information back. 83.El 84.Pp 85We always consider reading or writing to the kernel, from the user perspective. 86.It Fa g 87This integer describes to which subsystem the ioctl applies. 88Here are some examples: 89.Pp 90.Bl -tag -width xxxxx -compact 91.It '8' 92.Xr aac 4 93.It 'a' 94.Xr nata 4 95.It 'B' 96.Xr bpf 4 97.It 'C' 98.Xr ciss 4 99.It 'd' 100.Xr disklabel 5 101.It 'd' 102diskslice 103.It 'd' 104.Xr drm 4 105.It 'f' 106generic file-descriptor 107.It 'F' 108frame buffer 109.It 'h' 110.Xr HAMMER 5 111.It 'i' 112.Xr iic 4 113.It 'i' 114.Xr carp 4 115.It 'i' 116.Xr gre 4 117.It 'k' 118.Xr keyboard 4 119and 120.Xr syscons 4 121.It 'm' 122.Xr mem 4 123.It 'm' 124.Pa /dev/midi 125.It 'm' 126.Xr mtio 4 127.It 'M' 128.Xr sound 4 129mixer 130.It 'n' 131.Xr smb 4 132.It 'n' 133NetWare volume mount 134.It 'p' 135.Pa /dev/dsp 136and 137.Pa /dev/audio 138.It 'p' 139.Xr pci 4 140.It 'p' 141.Xr ppbus 4 142.It 'p' 143.Xr procfs 5 144.It 'q' 145.Pa /dev/sequencer 146.It 'r' 147random number generator 148.It 't' 149.Xr tty 4 150.It 't' 151.Xr tap 4 152.It 't' 153.Xr tun 4 154.It 't' 155SLIP ttys 156.It 'T' 157.Xr snp 4 158.\".It 'V' 159.\"VMware 160.El 161.It Fa n 162This number uniquely identifies the ioctl within the group. 163That said, two subsystems may share the same 164.Fa g , 165but there may be only one 166.Fa n 167for a given 168.Fa g . 169This is an unsigned 8 bit number. 170.It Fa t 171This specifies the type of the passed parameter. 172This one gets internally transformed to the size of the parameter, so 173for example, if you want to pass a structure, then you have to specify that 174structure and not a pointer to it or sizeof(struct MYDEV). 175.El 176.Pp 177In order for the new ioctl to be visible to the system, it is installed 178in either 179.In sys/ioctl.h or one of the files that are reached from 180.In sys/ioctl.h . 181.Sh RETURN VALUES 182A distinction must be made at this point. 183All 184.Fn *_ioctl 185routines from 186.Em within kernel 187should return either 0 for success 188or a defined error code, as described in 189.In sys/errno.h . 190At the libc level though a conversion takes place, so that eventually 191.Xr ioctl 2 192returns either 0 for success or -1 for failure, in which case the 193.Va errno 194variable is set accordingly. 195.Pp 196The use of magic numbers such as -1, to indicate that a given ioctl 197code was not handled, is strongly discouraged. 198The value -1 is bound to the 199.Er ERESTART 200pseudo-error, which is returned inside kernel to modify return to process. 201.Sh EXAMPLES 202Let's suppose that we want to pass an integer value to the kernel. 203From the user point of view, this is like writing to the kernel. 204So we define the ioctl as: 205.Bd -literal -offset indent 206#define MYDEVIOCTL _IOW('i', 25, int) 207.Ed 208.Pp 209Within the 210.Fn *_ioctl 211routine of the driver, it can be then accessed like: 212.Bd -literal -offset indent 213int 214mydev_ioctl(struct dev_ioctl_args *ap) 215{ 216 int error; 217 int *a; 218 219 switch (ap->a_cmd) { 220 case MYDEVIOCTL: 221 a = (int *)ap->data; 222 kprintf("Value passed from userspace: %d\\n", *a); 223 return (0); /* Success */ 224 break; 225 226 /* Handle other ioctls here */ 227 228 default: 229 /* Inappropriate ioctl for device */ 230 error = ENOTTY; 231 break; 232 } 233 234 return (error); 235} 236.Ed 237.Pp 238In userspace: 239.Bd -literal -offset indent 240int a = 101; 241if (ioctl(fd, MYDEVIOCTL, \*[Am]a) == -1) { 242 /* Handle failure */ 243} 244.Ed 245.Sh SEE ALSO 246.Xr ioctl 2 247