IOPL(2)                     Linux Programmer's Manual                    IOPL(2)

       iopl - change I/O privilege level

       #include <sys/io.h>

       int iopl(int level);

       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.

       On success, zero is returned.  On error, -1 is returned, and errno is set
       to indicate the error.

       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.

       iopl() is Linux-specific and should not be used in programs that are
       intended to be portable.

       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.

       ioperm(2), outb(2), capabilities(7)

       This page is part of release 5.11 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                              2021-03-22                            IOPL(2)