I386_IOPL(2) | System Calls Manual (i386) | I386_IOPL(2)

# NAME

`i386_iopl` — change the i386 I/O privilege level

# SYNOPSIS

i386 Architecture Library (libi386, -li386)
`#include <sys/types.h>`
`#include <machine/sysarch.h>`

int
`i386_iopl`(int iopl);

# DESCRIPTION

`i386_iopl`() sets the i386 I/O privilege level to the value specified by iopl.

This call may only be made by the superuser. Additionally, it is only permitted when the securelevel(7) is less than or equal to 0 or the machdep.allowaperture sysctl has been set to a non-zero value.

# RETURN VALUES

Upon successful completion, `i386_iopl`() returns 0. Otherwise, a value of -1 is returned and the global variable errno is set to indicate the error.

# ERRORS

`i386_iopl`() will fail if:

[`EPERM`]
  The caller was not the superuser, or the securelevel is greater than zero and machdep.allowaperture has not been set to a non-zero value.

# SEE ALSO

securelevel(7)

# REFERENCES

Intel, i386 Microprocessor Programmer's Reference Manual.

# WARNING

You can really hose your machine if you enable user-level I/O and write to hardware ports without care.

June 5, 2025 | Debian