ioperm(2) — Linux manual page

ioperm(2)                  System Calls Manual                 ioperm(2)

NAME

       ioperm - set port input/output permissions

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/io.h>

       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 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

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

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.

VERSIONS

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

STANDARDS

       Linux.

HISTORY

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

NOTES

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

SEE ALSO

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

COLOPHON

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Linux man-pages 6.9.1          2024-05-02                      ioperm(2)

Pages that refer to this page: fork(2), ioctl_console(2), iopl(2), outb(2), syscalls(2), unimplemented(2), mem(4), systemd.exec(5), capabilities(7)

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