iopl changes the I/O privilege level of the current process, as specified
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.
This call is mostly for the i386 architecture. On many other architectures it
does not exist or will always return an error.
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.