IOPL(2)

NAME
iopl - change I/O privilege level

SYNOPSIS
#include <unistd.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. 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.

SEE ALSO
ioperm(2)