iopl - change I/O privilege level
int iopl(int level));
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, run-
ning 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.
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
EINVAL level is greater than 3.
EPERM The current user is not the super-user.
Under libc5, the prototype for iopl() is given in
<unistd.h>, but glibc2 has this prototype in <sys/io.h>.
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 bit-
mapped you'd need 8kB of bitmaps/process, which is a bit
iopl is Linux specific and should not be used in processes
intended to be portable.