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+.\"
+.\" Copyright (c) 1996 Joerg Wunsch
+.\"
+.\" All rights reserved.
+.\"
+.\" This program is free software.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd October 3, 2004
+.Dt IO 4 i386
+.Os
+.Sh NAME
+.Nm io
+.Nd I/O privilege file
+.Sh SYNOPSIS
+.Cd "device io"
+.Sh DESCRIPTION
+The special file
+.Pa /dev/io
+is a controlled security hole that allows a process to gain I/O
+privileges
+(which are normally reserved for kernel-internal code).
+Any process that holds a file descriptor on
+.Pa /dev/io
+open will get its
+.Em IOPL
+bits in the flag register set, thus allowing it to perform direct
+I/O operations.
+This can be useful in order to write userland
+programs that handle some hardware directly.
+Note that even read-only access will grant the full I/O privileges.
+.Pp
+In addition to any file access permissions on
+.Pa /dev/io ,
+the kernel enforces that only the super-user may open this device.
+.Sh FILES
+.Bl -tag -width Pa -compact
+.It Pa /dev/io
+.El
+.Sh SEE ALSO
+.Xr i386_get_ioperm 2 ,
+.Xr i386_set_ioperm 2 ,
+.Xr mem 4
+.Sh HISTORY
+The
+.Nm
+file appeared in
+.Fx 1.0 .