Commit 2dcc51b3 authored by Flavio Suligoi's avatar Flavio Suligoi Committed by Jonathan Corbet
Browse files

docs: filesystems: add info about efivars content 



When an EFI variable is reading from:

/sys/firmware/efi/efivars

(for example using "hexdump"), the first 4 bytes of the
output are not the real EFI variable data, but the variable
attributes (in little-endian format).

Signed-off-by: default avatarFlavio Suligoi <f.suligoi@asem.it>
Link: https://lore.kernel.org/r/20200519084128.12756-1-f.suligoi@asem.it


Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent e2d467de

Documentation/filesystems/efivarfs.rst

+17 −0
Original line number Diff line number Diff line
@@ -24,3 +24,20 @@ files that are not well-known standardized variables are created 
as immutable files.  This doesn't prevent removal - "chattr -i" will work -

but it does prevent this kind of failure from being accomplished

accidentally.



.. warning ::

      When a content of an UEFI variable in /sys/firmware/efi/efivars is

      displayed, for example using "hexdump", pay attention that the first

      4 bytes of the output represent the UEFI variable attributes,

      in little-endian format.



      Practically the output of each efivar is composed of:



          +-----------------------------------+

          |4_bytes_of_attributes + efivar_data|

          +-----------------------------------+



*See also:*



- Documentation/admin-guide/acpi/ssdt-overlays.rst

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