efivars: Add Documentation

This patch documents the interface exposed by the 'efivars' module.

Signed-off-by: Mike Waychison <mikew@google.com>
Cc: Matt Domsch <Matt_Domsch@dell.com>,
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 75 insertions, 0 deletions

diff --git a/Documentation/ABI/stable/sysfs-firmware-efi-vars b/Documentation/ABI/stable/sysfs-firmware-efi-vars
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+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.