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
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:
- Takes nothing, and fills in the options node number.
- 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.
- 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
- 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.
- Writes the given value under the given name. The OPENPROM may refuse this
operation, in this case
- 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.
OPIOCGETNEXT, the next name after the empty string is the first name.
The following may result in rejection of an operation:
- The given node number is not zero and does not correspond to any valid node, or is zero where zero is not allowed.
- The requested operation requires permissions not specified at the call to
- The given name or value field exceeds the maximum allowed length (8191 bytes).
- Memory could not be allocated.
- The ioctl is not supported on this architecture.
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, and on arm64 since OpenBSD 6.1.
Due to limitations within the OPENPROM itself, these functions run at elevated priority and may adversely affect system performance.