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.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
.\" Portions extracted from linux/kernel/ioport.c (no copyright notice).
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" Modified Tue Aug 1 16:47 1995 by Jochen Karrer
.\" <cip307@cip.physik.uni-wuerzburg.de>
.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified Thu Jul 24 1997 by Nicols Lichtmaier <nick@debian.org>
.\" Modified Fri Nov 27 14:50:36 CET 1998 by Andries Brouwer <aeb@cwi.nl>
.\"
.TH IOPL 2 "24 July 1993" "Linux 0.99.11" "Linux Programmer's Manual"
.SH NAME
iopl \- change I/O privilege level
.SH SYNOPSIS
.B #include <sys/io.h>
.sp
.BI "int iopl(int " level );
.SH DESCRIPTION
.B iopl
changes the I/O privilege level of the current process, as specified in
.IR level .
This call is necessary to allow 8514-compatible X servers to run under
Linux. Since these X servers require access to all 65536 I/O ports, the
.B ioperm
call is not sufficient.
In addition to granting unrestricted I/O port access, running at a higher
I/O privilege level also allows the process to disable interrupts. This
will probably crash the system, and is not recommended.
Permissions are inherited by fork and exec.
The I/O privilege level for a normal process is 0.
.SH "RETURN VALUE"
On success, zero is returned. On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP 0.8i
.B EINVAL
.I level
is greater than 3.
.TP
.B EPERM
The current user is not the super-user.
.SH "COMPATIBILITY"
Under libc5, the prototype for
.BR iopl ()
was given in
.IR <unistd.h> .
.SH "NOTES FROM THE KERNEL SOURCE"
.B iopl
has to be used when you want to access the I/O ports beyond the 0x3ff
range: to get the full 65536 ports bitmapped you'd need 8kB of
bitmaps/process, which is a bit excessive.
.SH "CONFORMING TO"
\fBiopl\fP is Linux specific and should not be used in processes
intended to be portable.
.SH "SEE ALSO"
.BR ioperm (2)
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