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-rw-r--r--Documentation/filesystems/efivarfs.rst17
1 files changed, 17 insertions, 0 deletions
diff --git a/Documentation/filesystems/efivarfs.rst b/Documentation/filesystems/efivarfs.rst
index 90ac65683e7e..0551985821b8 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