NAME
nvram —
PReP nvram interface
SYNOPSIS
#include <machine/nvram.h>
DESCRIPTION
The file
/dev/nvram is an interface to the PReP NVRAM,
including the Global Environment Area. This interface is highly stylized;
ioctls are used for all operations. These ioctls refer to individual variables
in the Global Environment Area and their values.
The calls that take and/or return a variable use a pointer to an
int
variable for this purpose; others use a pointer to
an
struct pnviocdesc
descriptor, which contains a
variable and two counted strings. The first string comprises the fields
pnv_namelen
(an
int
) and
pnv_name
(a
char *
), giving
the name of a field. The second string comprises the fields
pnv_buflen
and
pnv_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:
-
-
- PNVIOCGETNEXTNAME
- Takes a variable name and returns the name of the following
variable. If a
NULL
is passed as the variable
name, the first variable name will be returned. If the last variable is
given as an argument, the ioctl will return
EINVAL
.
-
-
PNVIOCGET
- Fills in the value of the named property for the given
variable. If no such property is associated with that variable, the value
length is set to -1. If the named property exists but has no value, the
value length is set to 0.
-
-
PNVIOCSET
- Writes the given value under the given name.
-
-
PNVIOCGETNUMGE
- Returns the number of variables in the Global Environment
Area.
FILES
/dev/nvram
ERRORS
The following may result in rejection of an operation:
-
-
- [
EINVAL
]
- The given variable name does not exist; or the buffer set
up to retrieve values from the nvram was not large enough to hold the
result.
SEE ALSO
ioctl(2)
PowerPC Reference Platform Specification Version 1.1, Section
5.5
BUGS
Due to limitations within the
nvram itself, these functions
run at elevated priority and may adversely affect system performance.
PNVIOCSET
is not currently supported, making the
nvram driver read-only at this time.