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 27, 2009 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 '5' 92.Xr perfmon 4 93.It '8' 94.Xr aac 4 95.It 'a' 96.Xr nata 4 97.It 'B' 98.Xr bpf 4 99.It 'C' 100.Xr ciss 4 101.It 'd' 102.Xr disklabel 5 103.It 'd' 104diskslice 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 'n' 128.Xr smb 4 129.It 'n' 130NetWare volume mount 131.It 'p' 132.Pa /dev/dsp 133and 134.Pa /dev/audio 135.It 'p' 136.Xr pci 4 137.It 'p' 138.Xr ppbus 4 139.It 'P' 140.Xr apm 4 141.It 'q' 142.Pa /dev/sequencer 143.It 'r' 144.Xr ipf 4 145.It 'r' 146random number generator 147.It 't' 148.Xr tty 4 149.It 't' 150.Xr ppp 4 151.It 't' 152.Xr tap 4 153.It 't' 154.Xr tun 4 155.It 't' 156SLIP ttys 157.It 'T' 158.Xr snp 4 159.\".It 'V' 160.\"VMware 161.El 162.It Fa n 163This number uniquely identifies the ioctl within the group. 164That said, two subsystems may share the same 165.Fa g , 166but there may be only one 167.Fa n 168for a given 169.Fa g . 170This is an unsigned 8 bit number. 171.It Fa t 172This specifies the type of the passed parameter. 173This one gets internally transformed to the size of the parameter, so 174for example, if you want to pass a structure, then you have to specify that 175structure and not a pointer to it or sizeof(struct MYDEV). 176.El 177.Pp 178In order for the new ioctl to be visible to the system, it is installed 179in either 180.In sys/ioctl.h or one of the files that are reached from 181.In sys/ioctl.h . 182.Sh EXAMPLES 183Let's suppose that we want to pass an integer value to the kernel. 184From the user point of view, this is like writing to the kernel. 185So we define the ioctl as: 186.Bd -literal -offset indent 187#define MYDEVIOCTL _IOW('i', 25, int) 188.Ed 189.Pp 190Within the 191.Fn *_ioctl 192routine of the driver, it can be then accessed like: 193.Bd -literal -offset indent 194int 195mydev_ioctl(struct dev_ioctl_args *ap) 196{ 197 int error; 198 int *a; 199 200 switch (ap->a_cmd) { 201 case MYDEVIOCTL: 202 a = (int *)ap->data; 203 kprintf("Value passed from userspace: %d\\n", *a); 204 return (0); /* Success */ 205 break; 206 207 /* Handle other ioctls here */ 208 209 default: 210 /* Inappropriate ioctl for device */ 211 error = ENOTTY; 212 break; 213 } 214 215 return (error); 216} 217.Ed 218.Pp 219In userspace: 220.Bd -literal -offset indent 221int a = 101; 222if (ioctl(fd, MYDEVIOCTL, \*[Am]a) == -1) { 223 /* Handle failure */ 224} 225.Ed 226.Sh RETURN VALUES 227A distinction must be made at this point. 228All 229.Fn *_ioctl 230routines from 231.Em within kernel 232should return either 0 for success 233or a defined error code, as described in 234.In sys/errno.h . 235At the libc level though a conversion takes place, so that eventually 236.Xr ioctl 2 237returns either 0 for success or -1 for failure, in which case the 238.Va errno 239variable is set accordingly. 240.Pp 241The use of magic numbers such as -1, to indicate that a given ioctl 242code was not handled, is strongly discouraged. 243The value -1 is bound to the 244.Er ERESTART 245pseudo-error, which is returned inside kernel to modify return to process. 246.Sh SEE ALSO 247.Xr ioctl 2 248