NVRAM(4) (prep)

NVRAM(4) | Device Drivers Manual (prep) | NVRAM(4)

# 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.

March 1, 2007 | NetBSD 9.4