What: /sys/firmware/efi/vars
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Date: April 2004
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Contact: Matt Domsch <Matt_Domsch@dell.com>
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Description:
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This directory exposes interfaces for interactive with
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EFI variables. For more information on EFI variables,
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see 'Variable Services' in the UEFI specification
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(section 7.2 in specification version 2.3 Errata D).
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In summary, EFI variables are named, and are classified
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into separate namespaces through the use of a vendor
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GUID. They also have an arbitrary binary value
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associated with them.
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The efivars module enumerates these variables and
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creates a separate directory for each one found. Each
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directory has a name of the form "<key>-<vendor guid>"
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and contains the following files:
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=============== ========================================
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attributes: A read-only text file enumerating the
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EFI variable flags. Potential values
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include:
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EFI_VARIABLE_NON_VOLATILE
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EFI_VARIABLE_BOOTSERVICE_ACCESS
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EFI_VARIABLE_RUNTIME_ACCESS
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EFI_VARIABLE_HARDWARE_ERROR_RECORD
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EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS
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See the EFI documentation for an
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explanation of each of these variables.
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data: A read-only binary file that can be read
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to attain the value of the EFI variable
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guid: The vendor GUID of the variable. This
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should always match the GUID in the
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variable's name.
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raw_var: A binary file that can be read to obtain
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a structure that contains everything
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there is to know about the variable.
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For structure definition see "struct
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efi_variable" in the kernel sources.
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This file can also be written to in
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order to update the value of a variable.
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For this to work however, all fields of
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the "struct efi_variable" passed must
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match byte for byte with the structure
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read out of the file, save for the value
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portion.
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**Note** the efi_variable structure
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read/written with this file contains a
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'long' type that may change widths
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depending on your underlying
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architecture.
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size: As ASCII representation of the size of
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the variable's value.
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=============== ========================================
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In addition, two other magic binary files are provided
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in the top-level directory and are used for adding and
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removing variables:
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=============== ========================================
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new_var: Takes a "struct efi_variable" and
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instructs the EFI firmware to create a
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new variable.
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del_var: Takes a "struct efi_variable" and
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instructs the EFI firmware to remove any
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variable that has a matching vendor GUID
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and variable key name.
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=============== ========================================
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