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)

COLOPHON

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