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.