IOPL

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
NOTES FROM THE KERNEL SOURCE
CONFORMING TO
NOTES
SEE ALSO

NAME

iopl − change I/O privilege level

SYNOPSIS

#include <unistd.h> /* for libc5 */
#include <sys/io.h>
/* for glibc */

int iopl(int 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 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.

RETURN VALUE

On success, zero is returned. On error, −1 is returned, and errno is set appropriately.

ERRORS

EINVAL

level is greater than 3.

EPERM

The current user is not the super-user.

NOTES FROM THE KERNEL SOURCE

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.

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)