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 process, as specified by the two least significant
       bits in level.

       This call is necessary to allow 8514-compatible X servers to run under  Linux.   Since  these  X  servers
       require access to all 65536 I/O ports, the ioperm(2) call is not sufficient.

       In addition to granting unrestricted I/O port access, running at a higher I/O privilege level also allows
       the process to disable interrupts.  This will probably crash the system, and is not recommended.

       Permissions are not inherited by the child process created  by  fork(2)  and  are  not  preserved  across
       execve(2) (but see NOTES).

       The I/O privilege level for a normal process is 0.

       This  call  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 process 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 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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