Name
iopl — change I/O privilege level
DESCRIPTION
iopl
() changes the I/O
privilege level of the current process, as specified 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.
RETURN VALUE
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
ERRORS
- EINVAL
-
level
is
greater than 3.
- ENOSYS
-
This call is unimplemented.
- EPERM
-
The calling process has insufficient privilege to
call iopl
(); the
CAP_SYS_RAWIO
capability
is required.
CONFORMING TO
iopl
() is Linux specific and
should not be used in processes intended to be portable.
NOTES
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.
SEE ALSO
ioperm(2), capabilities(7)
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manual page may be incorrect or out-of-date.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 Fri Nov 27 14:50:36 CET 1998 by Andries Brouwer <aeb@cwi.nl>
Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
Added notes on capability requirements
|