---
name: "openprom"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/openprom"
---

# openprom(4)

OPENPROM interface

## NAME

**openprom** – OPENPROM interface

## SYNOPSIS

**#include \<machine/openpromio.h\>**

## DESCRIPTION

The file */dev/openprom* is an interface to the OPENPROM. This interface is highly stylized, ioctls are used for all operations. These ioctls refer to “nodes”, which are simply “magic” integer values describing data areas. Occasionally the number 0 may be used or returned instead, as described below.

The calls that take and/or return a node use a pointer to an *int* variable for this purpose; others use a pointer to a *struct* *opiocdesc* descriptor, which contains a node and two counted strings. The first string is comprised of the fields op\_namelen (an *int*) and op\_name (a *char* *\**), giving the name of a field. The second string is comprised of the fields op\_buflen and op\_buf, used analogously. These two counted strings work in a “value-result” fashion. At entry to the ioctl, the counts are expected to reflect the buffer size; on return, the counts are updated to reflect the buffer contents.

The following ioctls are supported:

- OPIOCGETOPTNODE

  Takes nothing, and fills in the options node number.

- OPIOCGETNEXT

  Takes a node number and returns the number of the following node. The node following the last node is number 0; the node following number 0 is the first node.

- OPIOCGETCHILD

  Takes a node number and returns the number of the first “child” of that node. This child may have siblings; these can be discovered by using OPIOCGETNEXT.

- OPIOCGET

  Fills in the value of the named property for the given node. If no such property is associated with that node, the value length is set to -1. If the named property exists but has no value, the value length is set to 0.

- OPIOCSET

  Writes the given value under the given name. The OPENPROM may refuse this operation, in this case EINVAL is returned.

- OPIOCNEXTPROP

  Finds the property whose name follows the given name in OPENPROM internal order. The resulting name is returned in the value field. If the named property is the last, the “next” name is the empty string. As with OPIOCGETNEXT, the next name after the empty string is the first name.

## FILES

*/dev/openprom*

## ERRORS

The following may result in rejection of an operation:

- \[EINVAL\]

  The given node number is not zero and does not correspond to any valid node, or is zero where zero is not allowed.

- \[EBADF\]

  The requested operation requires permissions not specified at the call to **open**().

- \[ENAMETOOLONG\]

  The given name or value field exceeds the maximum allowed length (8191 bytes).

- \[ENOMEM\]

  Memory could not be allocated.

- \[ENOTTY\]

  The ioctl is not supported on this architecture.

## SEE ALSO

[ioctl(2)](/ioctl/2.md), [eeprom(8)](/eeprom/8.md)

## HISTORY

The **openprom** interface first appeared in OpenBSD 3.0 for sparc64. It has been available on macppc since OpenBSD 4.3, on octeon since OpenBSD 6.0, on armv7 since OpenBSD 6.0, on arm64 since OpenBSD 6.1, on powerpc64 since OpenBSD 6.8, and on riscv64 since OpenBSD 7.0.

## BUGS

Due to limitations within the OPENPROM itself, these functions run at elevated priority and may adversely affect system performance.