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 appropriately.

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)

COLOPHON

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Linux                                              2020-08-13                                            IOPL(2)