.\" $NetBSD: io.4,v 1.4 2002/01/15 01:42:01 wiz Exp $
.\"
.\" Copyright (c) 1996 Joerg Wunsch
.\"
.\" All rights reserved.
.\"
.\" This program is free software.
.\"
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.\" are met:
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.\"    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
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.\"
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.\" $FreeBSD: src/share/man/man4/man4.i386/io.4,v 1.6.2.2 2000/12/12 10:00:55 ru Exp $
.\"
.Dd January 1, 1996
.Dt IO 4 i386
.Os
.Sh NAME
.Nm io
.Nd I/O privilege file
.Sh DESCRIPTION
.Bf -symbolic
This device is obsolete and is provided for compatibility purposes
only; use
.Xr i386_iopl 2
instead.
.Ef
.Pp
After opening
.Pa /dev/io
for writing
the process is granted full I/O privileges; closing the returned file
descriptor does
.Em not
result in revocation of these privileges.
The new I/O privileges can be useful in order to write userland
programs that handle some hardware directly.
.Pp
The entire access control is handled by the file access permissions
of
.Pa /dev/io ,
so care should be taken in granting rights for this device.
.Pp
I/O privilege on access to
.Pa /dev/io
is only granted if the kernel was built with the
.Dv COMPAT_10
option.
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /dev/io
.El
.Sh SEE ALSO
.Xr mem 4
.Sh HISTORY
The
.Nm
file appeared in
.Nx 1.0
after it was in the kernel for some time.