iopl

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 speci-
       fied by the two least significant bits in level.

       The I/O privilege level for a normal thread is 0.  Permissions are  in-
       herited 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 archi-
       tectures 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 privi-
              lege 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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       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

Linux                             2020-08-13                           IOPL(2)