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iopl — change I/O privilege level
#include <sys/io.h>
int
iopl( |
int level); |
iopl() changes the I/O
privilege level of the calling process, as specified by the
two least significant bits in 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 ioperm(2) 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(2) and execve(2).
The I/O privilege level for a normal process is 0.
This call is mostly for the i386 architecture. On many other architectures it does not exist or will always return an error.
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
level is
greater than 3.
This call is unimplemented.
The calling process has insufficient privilege to
call iopl(); the
CAP_SYS_RAWIO capability
is required to raise the I/O privilege level above its
current value.
iopl() is Linux-specific and
should not be used in programs that are intended to be
portable.
Libc5 treats it as a system call and has a prototype in
<unistd.h>
Glibc1 does not have a prototype. Glibc2 has a prototype both
in <sys/io.h>
and in <sys/perm.h>
Avoid the latter, it is available on i386 only.
This page is part of release 3.52 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man−pages/.
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Copyright 1993 Rickard E. Faith (faithcs.unc.edu) Portions extracted from linux/kernel/ioport.c (no copyright notice). %%%LICENSE_START(VERBATIM) 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 Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date.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. %%%LICENSE_END Modified Tue Aug 1 16:47 1995 by Jochen Karrer <cip307cip.physik.uni-wuerzburg.de> Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esrthyrsus.com> Modified Fri Nov 27 14:50:36 CET 1998 by Andries Brouwer <aebcwi.nl> Modified, 27 May 2004, Michael Kerrisk <mtk.manpagesgmail.com> Added notes on capability requirements |