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

       ioperm - set port input/output permissions

       #include <sys/io.h> /* 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 privileged

       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

       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.

       On success, zero is returned.  On error, -1 is returned, and errno is set
       to indicate the error.

       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.

       Before Linux 2.4, permissions were not inherited by a child created by

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

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

       This page is part of release 5.11 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                              2021-03-22                          IOPERM(2)