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| author |   Flavio Suligoi <f.suligoi@asem.it> | 2020-05-19 10:41:27 +0200 |
|---|---|---|
| committer |   Jonathan Corbet <corbet@lwn.net> | 2020-05-25 18:59:59 -0600 |
| commit | 2dcc51b3fe1708d3cda1b3fe9a30c09550791387 (patch) | |
| tree | 3ca0682142937227dd2b67166dfb30ee709acd9c /Documentation/filesystems | |
| parent | Documentation: LSM: Correct the basic LSM description (diff) | |
| download | wireguard-linux-2dcc51b3fe1708d3cda1b3fe9a30c09550791387.tar.xz wireguard-linux-2dcc51b3fe1708d3cda1b3fe9a30c09550791387.zip | |
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: Flavio Suligoi <f.suligoi@asem.it>
Link: https://lore.kernel.org/r/20200519084128.12756-1-f.suligoi@asem.it
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/efivarfs.rst | 17 |
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 |