IOPERM

Section: Linux Programmer's Manual (2)
Updated: 2007-06-15
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NAME

ioperm - set port input/output permissions

SYNOPSIS

#include <unistd.h> /* for libc5 */
#include <sys/io.h> /* for glibc */

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

DESCRIPTION

ioperm() sets the port access permission bits for the calling process for num bytes starting from port address from to the value turn_on. If turn_on is non-zero, the calling process must be privileged (CAP_SYS_RAWIO).

Only the first 0x3ff I/O ports can be specified in this manner. For more ports, the iopl(2) system call must be used.

Permissions are not inherited by the child created by fork(2). Permissions are preserved across execve(2); this is useful for giving port access permissions to non-privileged 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

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

ERRORS

EINVAL: Invalid values for from or num.
EIO: (on PowerPC) This call is not supported.
ENOMEM: Out of memory.
EPERM: The calling process has insufficient privilege.

CONFORMING TO

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

NOTES

Libc5 treats it as a system call and has a prototype in <unistd.h>. Glibc1 does not have a prototype. Glibc2 has a prototype both in <sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on i386 only.

COLOPHON

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