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
index 0000000..5def20b
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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.