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.Dd June 1, 2010 29.Dt IO 4 30.Os 31.Sh NAME 32.Nm io 33.Nd I/O privilege file 34.Sh SYNOPSIS 35.Cd "device io" 36.Pp 37.In sys/types.h 38.In sys/ioctl.h 39.In dev/io/iodev.h 40.In machine/iodev.h 41.Bd -literal 42struct iodev_pio_req { 43 u_int access; 44 u_int port; 45 u_int width; 46 u_int val; 47}; 48.Ed 49.Sh DESCRIPTION 50The special file 51.Pa /dev/io 52is a controlled security hole that allows a process to gain I/O 53privileges 54(which are normally reserved for kernel-internal code). 55This can be useful in order to write userland 56programs that handle some hardware directly. 57.Pp 58The usual operations on the device are to open it via the 59.Xr open 2 60interface and to send I/O requests to the file descriptor using the 61.Xr ioctl 2 62syscall. 63.Pp 64The 65.Xr ioctl 2 66requests available for 67.Pa /dev/io 68are mostly platform dependent, but there are also some in common between 69all of them. 70The 71.Dv IODEV_PIO 72is used by all the architectures in order to request that an I/O operation 73be performed. 74It takes a 'struct iodev_pio_req' argument that must be previously setup. 75.Pp 76The 77.Fa access 78member specifies the type of operation requested. 79It may be: 80.Bl -tag -width IODEV_PIO_WRITE 81.It Dv IODEV_PIO_READ 82The operation is an "in" type. 83A value will be read from the specified port 84(retrieved from the 85.Fa port 86member) and the result will be stored in the 87.Fa val 88member. 89.It Dv IODEV_PIO_WRITE 90The operation is a "out" type. 91The value will be fetched from the 92.Fa val 93member and will be written out to the specified port (defined as the 94.Fa port 95member). 96.El 97.Pp 98Finally, the 99.Fa width 100member specifies the size of the operand to be read/written, expressed 101in bytes. 102.Pp 103In addition to any file access permissions on 104.Pa /dev/io , 105the kernel enforces that only the super-user may open this device. 106.Sh LEGACY 107The 108.Pa /dev/io 109interface used to be very i386 specific and worked differently. 110The initial implementation simply raised the 111.Em IOPL 112of the current thread when 113.Xr open 2 114was called on the device. 115This behaviour is retained in the current implementation as legacy 116support for both i386 and amd64 architectures. 117.Sh SEE ALSO 118.Xr close 2 , 119.Xr i386_get_ioperm 2 , 120.Xr i386_set_ioperm 2 , 121.Xr ioctl 2 , 122.Xr open 2 , 123.Xr mem 4 124.Sh HISTORY 125The 126.Nm 127file appeared in 128.Fx 1.0 . 129