iopl(2) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | SEE ALSO

iopl(2)                    System Calls Manual                   iopl(2)

NAME         top

       iopl - change I/O privilege level

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <sys/io.h>

       [[deprecated]] int iopl(int level);

DESCRIPTION         top

       iopl() changes the I/O privilege level of the calling thread, as
       specified by the two least significant bits in level.

       The I/O privilege level for a normal thread is 0.  Permissions
       are inherited from parents to children.

       This call is deprecated, is significantly slower than ioperm(2),
       and is only provided for older X servers which require access to
       all 65536 I/O ports.  It is mostly for the i386 architecture.  On
       many other architectures it does not exist or will always return
       an error.

RETURN VALUE         top

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

ERRORS         top

       EINVAL level is greater than 3.

       ENOSYS This call is unimplemented.

       EPERM  The calling thread has insufficient privilege to call
              iopl(); the CAP_SYS_RAWIO capability is required to raise
              the I/O privilege level above its current value.

VERSIONS         top

       glibc2 has a prototype both in <sys/io.h> and in <sys/perm.h>.
       Avoid the latter, it is available on i386 only.

STANDARDS         top

       Linux.

HISTORY         top

       Prior to Linux 5.5 iopl() allowed the thread to disable
       interrupts while running at a higher I/O privilege level.  This
       will probably crash the system, and is not recommended.

       Prior to Linux 3.7, on some architectures (such as i386),
       permissions were inherited by the child produced by fork(2) and
       were preserved across execve(2).  This behavior was inadvertently
       changed in Linux 3.7, and won't be reinstated.

SEE ALSO         top

       ioperm(2), outb(2), capabilities(7)

Linux man-pages (unreleased)   2024-05-02                        iopl(2)

Pages that refer to this page: ioperm(2)outb(2)syscalls(2)unimplemented(2)systemd.exec(5)capabilities(7)