Section: Linux Programmer's Manual (2)
iopl - change I/O privilege level
int iopl(int level);
changes the I/O privilege level of the calling thread,
as specified by the two least significant bits in
The I/O privilege level for a normal thread is 0.
Permissions are inherited from parents to children.
This call is deprecated, is significantly slower than
and is only provided for older X servers which require
access to all 65536 I/O ports.
It is mostly for the i386 architecture.
On many other architectures it does not exist or will always
return an error.
On success, zero is returned.
On error, -1 is returned, and
is set appropriately.
is greater than 3.
This call is unimplemented.
The calling thread has insufficient privilege to call
capability is required to raise the I/O privilege level
above its current value.
is Linux-specific and should not be used in programs that are
intended to be portable.
Glibc2 has a prototype both in
Avoid the latter, it is available on i386 only.
Prior to Linux 5.5
allowed the thread to disable interrupts while running
at a higher I/O privilege level.
This will probably crash the system, and is not recommended.
Prior to Linux 3.7,
on some architectures (such as i386), permissions
inherited by the child produced by
and were preserved across
This behavior was inadvertently changed in Linux 3.7,
and won't be reinstated.
This page is part of release 5.10 of the Linux
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