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IOPL(2) Linux Programmer's Manual IOPL(2)
NAME
iopl - change I/O privilege level
SYNOPSIS
#include <sys/io.h>
int iopl(int level);
DESCRIPTION
iopl() changes the I/O privilege level of the calling thread, as specified by the two least significant bits in level.
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 ioperm(2), 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.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set to indicate the error.
ERRORS
EINVAL level is greater than 3.
ENOSYS This call is unimplemented.
EPERM The calling thread has insufficient privilege to call iopl(); the CAP_SYS_RAWIO capability is required to raise the I/O privilege level above its current
value.
CONFORMING TO
iopl() is Linux-specific and should not be used in programs that are intended to be portable.
NOTES
Glibc2 has a prototype both in <sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on i386 only.
Prior to Linux 5.5 iopl() 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 were inherited by the child produced by fork(2) and were preserved across execve(2). This
behavior was inadvertently changed in Linux 3.7, and won't be reinstated.
SEE ALSO
ioperm(2), outb(2), capabilities(7)
Linux 2021-03-22 IOPL(2)