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Manpage of IOPL

IOPL

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.
 

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.  

COMPATIBILITY

Under libc5, the prototype for iopl() was given in <unistd.h>.  

SEE ALSO

ioperm(2)


 

Index

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

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