.\"	$OpenBSD: x86_64_iopl.2,v 1.1 2004/02/26 00:10:54 deraadt Exp $
.\"	$NetBSD: x86_64_iopl.2,v 1.3 1996/02/27 22:57:25 jtc Exp $
.\"
.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by John T. Kohl and Charles M. Hannum.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	   This product includes software developed by the NetBSD
.\"	   Foundation, Inc. and its contributors.
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
.\"    contributors may be used to endorse or promote products derived
.\"    from this software without specific prior written permission.
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.\"
.Dd October 14, 1995
.Dt X86_64_IOPL 2
.Os
.Sh NAME
.Nm x86_64_iopl
.Nd change the x86_64 I/O privilege level
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <machine/sysarch.h>
.Ft int
.Fn x86_64_iopl "int iopl"
.Sh DESCRIPTION
.Fn x86_64_iopl
sets the x86_64 I/O privilege level to the value specified by
.Ar iopl .
This call is restricted to the superuser.
.Pp
.Sy Note:
Code using the
.Fn x86_64_iopl
function must be compiled using
.Cm -lx86_64 .
.Sh RETURN VALUES
Upon successful completion,
.Fn x86_64_iopl
returns 0.
Otherwise, a value of \-1 is returned and the global
variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn x86_64_iopl
will fail if:
.Bl -tag -width [EINVAL]
.It Bq Er EPERM
The caller was not the superuser.
.El
.Sh SEE ALSO
.Xr x86_64_get_ioperm 2 ,
.Xr x86_64_set_ioperm 2
.Sh REFERENCES
.Rs
.%A Intel
.%T AMD64 Microprocessor Programmer's Reference Manual
.Re
.Sh WARNING
You can really hose your machine if you enable user-level I/O and
write to hardware ports without care.