Documentation/ABI/stable/sysfs-firmware-efi-vars

   1 What:           /sys/firmware/efi/vars
   2 Date:           April 2004
   3 Contact:        Matt Domsch <Matt_Domsch@dell.com>
   4 Description:
   5                 This directory exposes interfaces for interactive with
   6                 EFI variables.  For more information on EFI variables,
   7                 see 'Variable Services' in the UEFI specification
   8                 (section 7.2 in specification version 2.3 Errata D).
   9
  10                 In summary, EFI variables are named, and are classified
  11                 into separate namespaces through the use of a vendor
  12                 GUID.  They also have an arbitrary binary value
  13                 associated with them.
  14
  15                 The efivars module enumerates these variables and
  16                 creates a separate directory for each one found.  Each
  17                 directory has a name of the form "<key>-<vendor guid>"
  18                 and contains the following files:
  19
  20                 attributes:     A read-only text file enumerating the
  21                                 EFI variable flags.  Potential values
  22                                 include:
  23
  24                                 EFI_VARIABLE_NON_VOLATILE
  25                                 EFI_VARIABLE_BOOTSERVICE_ACCESS
  26                                 EFI_VARIABLE_RUNTIME_ACCESS
  27                                 EFI_VARIABLE_HARDWARE_ERROR_RECORD
  28                                 EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS
  29
  30                                 See the EFI documentation for an
  31                                 explanation of each of these variables.
  32
  33                 data:           A read-only binary file that can be read
  34                                 to attain the value of the EFI variable
  35
  36                 guid:           The vendor GUID of the variable.  This
  37                                 should always match the GUID in the
  38                                 variable's name.
  39
  40                 raw_var:        A binary file that can be read to obtain
  41                                 a structure that contains everything
  42                                 there is to know about the variable.
  43                                 For structure definition see "struct
  44                                 efi_variable" in the kernel sources.
  45
  46                                 This file can also be written to in
  47                                 order to update the value of a variable.
  48                                 For this to work however, all fields of
  49                                 the "struct efi_variable" passed must
  50                                 match byte for byte with the structure
  51                                 read out of the file, save for the value
  52                                 portion.
  53
  54                                 **Note** the efi_variable structure
  55                                 read/written with this file contains a
  56                                 'long' type that may change widths
  57                                 depending on your underlying
  58                                 architecture.
  59
  60                 size:           As ASCII representation of the size of
  61                                 the variable's value.
  62
  63
  64                 In addition, two other magic binary files are provided
  65                 in the top-level directory and are used for adding and
  66                 removing variables:
  67
  68                 new_var:        Takes a "struct efi_variable" and
  69                                 instructs the EFI firmware to create a
  70                                 new variable.
  71
  72                 del_var:        Takes a "struct efi_variable" and
  73                                 instructs the EFI firmware to remove any
  74                                 variable that has a matching vendor GUID
  75                                 and variable key name.