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: Flavio Suligoi <f.suligoi@xxxxxxx> --- Documentation/filesystems/efivarfs.rst | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/Documentation/filesystems/efivarfs.rst b/Documentation/filesystems/efivarfs.rst index 90ac656..6380336 100644 --- a/Documentation/filesystems/efivarfs.rst +++ b/Documentation/filesystems/efivarfs.rst @@ -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`` -- 2.7.4
