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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 process, as spec-
     ified 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 inter-
     rupts.  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 architec-
     tures 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 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 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.