openprom - PROM monitor configuration interface


#include <sys/fcntl.h>

#include <sys/types.h>

#include <sys/openpromio.h>

open("/dev/openprom", mode);


The internal encoding of the configuration information stored in EEPROM
or NVRAM varies from model to model, and on some systems the encoding is
"hidden" by the firmware. The openprom driver provides a consistent
interface that allows a user or program to inspect and modify that
configuration, using ioctl(2) requests. These requests are defined in

struct openpromio {
uint_t oprom_size; /* real size of following data */
union {
char b[1]; /* NB: Adjacent, Null terminated */
int i;
} opio_u;
#define oprom_array opio_u.b /* property name/value array */
#define oprom_node opio_u.i /* nodeid from navigation config-ops */
#define oprom_len opio_u.i /* property len from OPROMGETPROPLEN */
#define OPROMMAXPARAM 32768 /* max size of array (advisory) */

For all ioctl(2) requests, the third parameter is a pointer to a struct
openpromio. All property names and values are null-terminated strings;
the value of a numeric option is its ASCII representation.

For the raw ioctl(2) operations shown below that explicitly or implicitly
specify a nodeid, an error may be returned. This is due to the removal of
the node from the firmware device tree by a Dynamic Reconfiguration
operation. Programs should decide if the appropriate response is to
restart the scanning operation from the beginning or terminate, informing
the user that the tree has changed.


This ioctl takes the null-terminated name of a
property in the oprom_array and returns its null-
terminated value (overlaying its name). oprom_size
should be set to the size of oprom_array; on return it
will contain the size of the returned value. If the
named property does not exist, or if there is not
enough space to hold its value, then oprom_size will
be set to zero. See BUGS below.

This ioctl takes two adjacent strings in oprom_array;
the null-terminated property name followed by the
null-terminated value.

This ioctl is similar to OPROMSETOPT, except that it
uses the difference between the actual user array size
and the length of the property name plus its null

This ioctl is used to retrieve properties
sequentially. The null-terminated name of a property
is placed into oprom_array and on return it is
replaced with the null-terminated name of the next
property in the sequence, with oprom_size set to its
length. A null string on input means return the name
of the first property; an oprom_size of zero on output
means there are no more properties.

These ioctls provide an interface to the raw
config_ops operations in the PROM monitor. One can use
them to traverse the system device tree; see

This ioctl provides an interface to the property
length raw config op. It takes the name of a property
in the buffer, and returns an integer in the buffer.
It returns the integer -1 if the property does not
exist; 0 if the property exists, but has no value (a
boolean property); or a positive integer which is the
length of the property as reported by the PROM
monitor. See BUGS below.

This ioctl returns an arbitrary and platform-dependent
NULL-terminated string in oprom_array, representing
the underlying version of the firmware.


There are too many opens of the /dev/openprom device.

A bad address has been passed to an ioctl(2) routine.

The size value was invalid, or (for OPROMSETOPT) the
property does not exist, or an invalid ioctl is being issued,
or the ioctl is not supported by the firmware, or the nodeid
specified does not exist in the firmware device tree.

The kernel could not allocate space to copy the user's

Attempts have been made to write to a read-only entity, or read
from a write only entity.

Attempting to open a non-existent device.


Example 1: oprom_array Data Allocation and Reuse

The following example shows how the oprom_array is allocated and reused
for data returned by the driver.

* This program opens the openprom device and prints the platform
* name (root node name property) and the prom version.
* NOTE: /dev/openprom is readable only by user 'root' or group 'sys'.
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/openpromio.h>
#define min(a, b) (a < b ? a : b)
#define max(a, b) (a > b ? a : b)
#define MAXNAMESZ 32 /* Maximum property *name* size */
#define BUFSZ 1024 /* A Handly default buffer size */
#define MAXVALSZ (BUFSZ - sizeof (int))
static char *promdev = "/dev/openprom";
* Allocate an openpromio structure big enough to contain
* a bufsize'd oprom_array. Zero out the structure and
* set the oprom_size field to bufsize.
static struct openpromio *
opp_zalloc(size_t bufsize)
struct openpromio *opp;
opp = malloc(sizeof (struct openpromio) + bufsize);
(void) memset(opp, 0, sizeof (struct openpromio) + bufsize);
opp->oprom_size = bufsize;
return (opp);
* Free a 'struct openpromio' allocated by opp_zalloc
static void
opp_free(struct openpromio *opp)
* Get the peer node of the given node. The root node is the peer of zero.
* After changing nodes, property lookups apply to that node. The driver
* 'remembers' what node you are in.
static int
peer(int nodeid, int fd)
struct openpromio *opp;
int i;
opp = opp_zalloc(sizeof (int));
opp->oprom_node = nodeid;
if (ioctl(fd, OPROMNEXT, opp) < 0) {
i = opp->oprom_node;
struct openpromio *opp;
int fd, proplen;
size_t buflen;
if ((fd = open(promdev, O_RDONLY)) < 0) {
fprintf(stderr, "Cannot open openprom device\n");
* Get and print the length and value of the
* root node 'name' property
(void) peer(0, fd); /* Navigate to the root node */
* Allocate an openpromio structure sized big enough to
* take the string "name" as input and return the int-sized
* length of the 'name' property.
* Then, get the length of the 'name' property.
buflen = max(sizeof (int), strlen("name") + 1);
opp = opp_zalloc(buflen);
(void) strcpy(opp->oprom_array, "name");
if (ioctl(fd, OPROMGETPROPLEN, opp) < 0) {
/* exit(1); */
proplen = 0; /* down-rev driver? */
} else
proplen = opp->oprom_len;
if (proplen == -1) {
printf("'name' property does not exist!\n");
exit (1);
* Allocate an openpromio structure sized big enough
* to take the string 'name' as input and to return
* 'proplen + 1' bytes. Then, get the value of the
* 'name' property. Note how we make sure to size the
* array at least one byte more than the returned length
* to guarantee NULL termination.
buflen = (proplen ? proplen + 1 : MAXVALSZ);
buflen = max(buflen, strlen("name") + 1);
opp = opp_zalloc(buflen);
(void) strcpy(opp->oprom_array, "name");
if (ioctl(fd, OPROMGETPROP, opp) < 0) {
if (opp->oprom_size != 0)
printf("Platform name <%s> property len <%d>\n",
opp->oprom_array, proplen);
* Allocate an openpromio structure assumed to be
* big enough to get the 'prom version string'.
* Get and print the prom version.
opp->oprom_size = MAXVALSZ;
if (ioctl(fd, OPROMGETVERSION, opp) < 0) {
printf("Prom version <%s>\n", opp->oprom_array);
(void) close(fd);
return (0);


PROM monitor configuration interface


ioctl(2), mem(4D), eeprom(8), monitor(8), prtconf(8)


There should be separate return values for non-existent properties as
opposed to not enough space for the value.

An attempt to set a property to an illegal value results in the PROM
setting it to some legal value, with no error being returned. An
OPROMGETOPT should be performed after an OPROMSETOPT to verify that the
set worked.

Some PROMS lie about the property length of some string properties,
omitting the NULL terminator from the property length. The openprom
driver attempts to transparently compensate for these bugs when returning
property values by NULL terminating an extra character in the user
buffer if space is available in the user buffer. This extra character is
excluded from the oprom_size field returned from OPROMGETPROP and
OPROMGETOPT and excluded in the oprom_len field returned from
OPROMGETPROPLEN but is returned in the user buffer from the calls that
return data, if the user buffer is allocated at least one byte larger
than the property length.

January 13, 1997 OPENPROM(4D)