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 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 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.

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 thread has insufficient privilege.

CONFORMING TO

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

NOTES

       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 <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.

SEE ALSO

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

COLOPHON

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