iopl
Hurricane Electric Internet Services
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 pro-
cess, 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, run-
ning at a higher I/O privilege level also allows the pro-
cess 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)
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Hurricane Electric.
All Rights Reserved.