1.\" 2.\" Copyright (c) 1996 Joerg Wunsch 3.\" 4.\" All rights reserved. 5.\" 6.\" This program is free software. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 18.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 21.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27.\" 28.\" $FreeBSD$ 29.\" 30.Dd June 01, 2010 31.Dt IO 4 32.Os 33.Sh NAME 34.Nm io 35.Nd I/O privilege file 36.Sh SYNOPSIS 37.Cd "device io" 38.Pp 39.In sys/types.h 40.In sys/ioctl.h 41.In dev/io/iodev.h 42.In machine/iodev.h 43.Bd -literal 44struct iodev_pio_req { 45 u_int access; 46 u_int port; 47 u_int width; 48 u_int val; 49}; 50.Ed 51.Sh DESCRIPTION 52The special file 53.Pa /dev/io 54is a controlled security hole that allows a process to gain I/O 55privileges 56(which are normally reserved for kernel-internal code). 57This can be useful in order to write userland 58programs that handle some hardware directly. 59.Pp 60The usual operations on the device are to open it via the 61.Xr open 2 62interface and to send I/O requests to the file descriptor using the 63.Xr ioctl 2 64syscall. 65.Pp 66The 67.Xr ioctl 2 68requests available for 69.Pa /dev/io 70are mostly platform dependent, but there are also some in common between 71all of them. 72The 73.Dv IODEV_PIO 74is used by all the architectures in order to request that an I/O operation 75be performed. 76It takes a 'struct iodev_pio_req' argument that must be previously setup. 77.Pp 78The 79.Fa access 80member specifies the type of operation requested. 81It may be: 82.Bl -tag -width IODEV_PIO_WRITE 83.It Dv IODEV_PIO_READ 84The operation is an "in" type. 85A value will be read from the specified port 86(retrieved from the 87.Fa port 88member) and the result will be stored in the 89.Fa val 90member. 91.It Dv IODEV_PIO_WRITE 92The operation is a "out" type. 93The value will be fetched from the 94.Fa val 95member and will be written out to the specified port (defined as the 96.Fa port 97member). 98.El 99.Pp 100Finally, the 101.Fa width 102member specifies the size of the operand to be read/written, expressed 103in bytes. 104.Pp 105In addition to any file access permissions on 106.Pa /dev/io , 107the kernel enforces that only the super-user may open this device. 108.Sh LEGACY 109The 110.Pa /dev/io 111interface used to be very i386 specific and worked differently. 112The initial implementation simply raised the 113.Em IOPL 114of the current thread when 115.Xr open 2 116was called on the device. 117This behaviour is retained in the current implementation as legacy 118support for both i386 and amd64 architectures. 119.Sh SEE ALSO 120.Xr close 2 , 121.Xr i386_get_ioperm 2 , 122.Xr i386_set_ioperm 2 , 123.Xr ioctl 2 , 124.Xr open 2 , 125.Xr mem 4 126.Sh HISTORY 127The 128.Nm 129file appeared in 130.Fx 1.0 . 131