summaryrefslogtreecommitdiffstats
path: root/Documentation/filesystems/efivarfs.rst
diff options
context:
space:
mode:
authorSang-Heon Jeon <ekffu200098@gmail.com>2026-08-24 01:18:14 +0900
committerJulia Lawall <Julia.Lawall@inria.fr>2026-08-23 22:12:11 +0200
commit2bd30b8dc75b823dd7bbef9d7bc68e1fd7ecee5c (patch)
treedcc4da1d99f17541c5590ac63c77da4bf372a4ab /Documentation/filesystems/efivarfs.rst
downloadlinux-stable-2bd30b8dc75b823dd7bbef9d7bc68e1fd7ecee5c.tar.gz
linux-stable-2bd30b8dc75b823dd7bbef9d7bc68e1fd7ecee5c.zip
coccinelle: alloc_cast: drop removed allocatorsgrafted
- pci_alloc_consistent() and pci_zalloc_consistent() were removed by commit 7968778914e5 ("PCI: Remove the deprecated "pci-dma-compat.h" API") - kmem_alloc() was removed by commit f078d4ea8276 ("xfs: convert kmem_alloc() to kmalloc()") - kmem_zalloc() was removed by commit 10634530f7ba ("xfs: convert kmem_zalloc() to kzalloc()") - kmem_zone_alloc() and kmem_zone_zalloc() were removed by commit bae633a4a283 ("xfs: remove xfs_zone_{alloc,zalloc} helpers") So drop them from the rules. No functional change. Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Diffstat (limited to 'Documentation/filesystems/efivarfs.rst')
-rw-r--r--Documentation/filesystems/efivarfs.rst43
1 files changed, 43 insertions, 0 deletions
diff --git a/Documentation/filesystems/efivarfs.rst b/Documentation/filesystems/efivarfs.rst
new file mode 100644
index 000000000..f646c3f09
--- /dev/null
+++ b/Documentation/filesystems/efivarfs.rst
@@ -0,0 +1,43 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================================
+efivarfs - a (U)EFI variable filesystem
+=======================================
+
+The efivarfs filesystem was created to address the shortcomings of
+using entries in sysfs to maintain EFI variables. The old sysfs EFI
+variables code only supported variables of up to 1024 bytes. This
+limitation existed in version 0.99 of the EFI specification, but was
+removed before any full releases. Since variables can now be larger
+than a single page, sysfs isn't the best interface for this.
+
+Variables can be created, deleted and modified with the efivarfs
+filesystem.
+
+efivarfs is typically mounted like this::
+
+ mount -t efivarfs none /sys/firmware/efi/efivars
+
+Due to the presence of numerous firmware bugs where removing non-standard
+UEFI variables causes the system firmware to fail to POST, efivarfs
+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/removed/sysfs-firmware-efi-vars