.\" $NetBSD: nvram.4,v 1.5 2009/05/27 19:28:42 wiz Exp $
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.\" Copyright (c) 2007 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Tim Rightnour
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.Dd March 1, 2007
.Dt NVRAM 4 prep
.Os
.Sh NAME
.Nm nvram
.Nd PReP nvram interface
.Sh SYNOPSIS
.In machine/nvram.h
.Sh DESCRIPTION
The file
.Nm /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.
.Pp
The calls that take and/or return a variable
use a pointer to an
.Li int
variable for this purpose;
others use a pointer to an
.Li struct pnviocdesc
descriptor,
which contains a variable and two counted strings.
The first string comprises the fields
.Li pnv_namelen
(an
.Li int )
and
.Li pnv_name
(a
.Li "char *" ) ,
giving the name of a field.
The second string comprises the fields
.Li pnv_buflen
and
.Li pnv_buf ,
used analogously.
These two counted strings work in a
.Dq 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.
.Pp
The following ioctls are supported:
.Bl -tag -width PNVIOCGETNEXTNAME
.It PNVIOCGETNEXTNAME
Takes a variable name and returns the name of the following variable.
If a
.Dv 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
.Er EINVAL .
.It Dv 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.
.It Dv PNVIOCSET
Writes the given value under the given name.
.It Dv PNVIOCGETNUMGE
Returns the number of variables in the Global Environment Area.
.El
.Sh FILES
.Pa /dev/nvram
.Sh ERRORS
The following may result in rejection of an operation:
.Bl -tag -width Er
.It Bq Er 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.
.El
.Sh SEE ALSO
.Xr ioctl 2
.Pp
.Pa PowerPC Reference Platform Specification Version 1.1, Section 5.5
.Sh BUGS
Due to limitations within the
.Nm
itself, these functions run at elevated priority
and may adversely affect system performance.
.Pp
.Dv PNVIOCSET
is not currently supported, making the
.Nm
driver read-only at this time.