ioperm(2) — Linux manual page


IOPERM(2)                 Linux Programmer's Manual                IOPERM(2)

NAME         top

       ioperm - set port input/output permissions

SYNOPSIS         top

       #include <sys/io.h> /* for glibc */

       int ioperm(unsigned long from, unsigned long num, int turn_on);

DESCRIPTION         top

       ioperm() sets the port access permission bits for the calling thread
       for num bits starting from port address from.  If turn_on is nonzero,
       then permission for the specified bits is enabled; otherwise it is
       disabled.  If turn_on is nonzero, the calling thread must be
       privileged (CAP_SYS_RAWIO).

       Before Linux 2.6.8, only the first 0x3ff I/O ports could be specified
       in this manner.  For more ports, the iopl(2) system call had to be
       used (with a level argument of 3).  Since Linux 2.6.8, 65,536 I/O
       ports can be specified.

       Permissions are inherited by the child created by fork(2) (but see
       NOTES).  Permissions are preserved across execve(2); this is useful
       for giving port access permissions to unprivileged programs.

       This call is mostly for the i386 architecture.  On many other
       architectures it does not exist or will always return an error.

RETURN VALUE         top

       On success, zero is returned.  On error, -1 is returned, and errno is
       set appropriately.

ERRORS         top

       EINVAL Invalid values for from or num.

       EIO    (on PowerPC) This call is not supported.

       ENOMEM Out of memory.

       EPERM  The calling thread has insufficient privilege.

CONFORMING TO         top

       ioperm() is Linux-specific and should not be used in programs
       intended to be portable.

NOTES         top

       The /proc/ioports file shows the I/O ports that are currently
       allocated on the system.

       Before Linux 2.4, permissions were not inherited by a child created
       by fork(2).

       Glibc has an ioperm() prototype both in <sys/io.h> and in
       <sys/perm.h>.  Avoid the latter, it is available on i386 only.

SEE ALSO         top

       iopl(2), outb(2), capabilities(7)

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2017-09-15                        IOPERM(2)

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