efivars: Add Documentation

What:		/sys/firmware/efi/vars

Date:		April 2004

Contact:	Matt Domsch <Matt_Domsch@dell.com>

Description:

		This directory exposes interfaces for interactive with

		EFI variables.  For more information on EFI variables,

		see 'Variable Services' in the UEFI specification

		(section 7.2 in specification version 2.3 Errata D).

		In summary, EFI variables are named, and are classified

		into separate namespaces through the use of a vendor

		GUID.  They also have an arbitrary binary value

		associated with them.

		The efivars module enumerates these variables and

		creates a separate directory for each one found.  Each

		directory has a name of the form "<key>-<vendor guid>"

		and contains the following files:

		attributes:	A read-only text file enumerating the

				EFI variable flags.  Potential values

				include:

				EFI_VARIABLE_NON_VOLATILE

				EFI_VARIABLE_BOOTSERVICE_ACCESS

				EFI_VARIABLE_RUNTIME_ACCESS

				EFI_VARIABLE_HARDWARE_ERROR_RECORD

				EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS

				See the EFI documentation for an

				explanation of each of these variables.

		data:		A read-only binary file that can be read

				to attain the value of the EFI variable

		guid:		The vendor GUID of the variable.  This

				should always match the GUID in the

				variable's name.

		raw_var:	A binary file that can be read to obtain

				a structure that contains everything

				there is to know about the variable.

				For structure definition see "struct

				efi_variable" in the kernel sources.

				This file can also be written to in

				order to update the value of a variable.

				For this to work however, all fields of

				the "struct efi_variable" passed must

				match byte for byte with the structure

				read out of the file, save for the value

				portion.

				**Note** the efi_variable structure

				read/written with this file contains a

				'long' type that may change widths

				depending on your underlying

				architecture.

		size:		As ASCII representation of the size of

				the variable's value.

		In addition, two other magic binary files are provided

		in the top-level directory and are used for adding and

		removing variables:

		new_var:	Takes a "struct efi_variable" and

				instructs the EFI firmware to create a

				new variable.

		del_var:	Takes a "struct efi_variable" and

				instructs the EFI firmware to remove any

				variable that has a matching vendor GUID

				and variable key name.