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>

diff --git a/Documentation/ABI/stable/sysfs-firmware-efi-vars b/Documentation/ABI/stable/sysfs-firmware-efi-vars
new file mode 100644 (file)
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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.