IOPL

This document was created by man2html using the manual pages.
Section: Linux Programmer's Manual (2)
Updated: 1993-07-24
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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 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.

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.

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