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IOPL(2) Linux Programmer's Manual IOPL(2)
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, 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.
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.
iopl is Linux specific and should not be used in processes intended to be portable.
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.
Linux 0.99.11 1993-07-24 IOPL(2)
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