ioperm - set port input/output permissions
#include /* for libc5 */
#include /* for glibc */
int ioperm(unsigned long from, unsigned long num, int turn_on);
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
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 not inherited by the child created by fork(2);
following a fork(2) the child must turn on those permissions that it
needs. 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.
On success, zero is returned. On error, -1 is returned, and errno is
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.
ioperm() is Linux-specific and should not be used in programs
intended to be portable.
The /proc/ioports file shows the I/O ports that are currently
allocated on the system.
Libc5 treats it as a system call and has a prototype in .
Glibc1 does not have a prototype. Glibc2 has a prototype both in
and in . Avoid the latter, it is available on
iopl(2), outb(2), capabilities(7)
This page is part of release 3.55 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2013-03-12 IOPERM(2)