IOPL
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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NAME
iopl - change I/O privilege level
SYNOPSIS
#include <sys/io.h>
int iopl(int level);
DESCRIPTION
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 not inherited by the child process created by
fork(2)
and are not preserved across
execve(2)
(but see NOTES).
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 to raise the I/O privilege level
above its current value.
CONFORMING TO
iopl()
is Linux-specific and should not be used in programs that are
intended to be portable.
NOTES
Glibc2 has a prototype both in
<sys/io.h>
and in
<sys/perm.h>.
Avoid the latter, it is available on i386 only.
Prior to Linux 3.7,
on some architectures (such as i386), permissions
were
inherited by the child produced by
fork(2)
and were preserved across
execve(2).
This behavior was inadvertently changed in Linux 3.7,
and won't be reinstated.
SEE ALSO
ioperm(2),
outb(2),
capabilities(7)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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