2026-01-21 18:59:54 +08:00
|
|
|
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
|
|
|
|
|
|
Large Extended Attribute Values
|
|
|
|
|
-------------------------------
|
|
|
|
|
|
|
|
|
|
To enable ext4 to store extended attribute values that do not fit in the
|
|
|
|
|
inode or in the single extended attribute block attached to an inode,
|
2026-01-29 22:25:33 +08:00
|
|
|
the EA_INODE feature allows us to store the value in the data blocks of
|
2026-01-21 18:59:54 +08:00
|
|
|
a regular file inode. This “EA inode” is linked only from the extended
|
|
|
|
|
attribute name index and must not appear in a directory entry. The
|
2026-01-29 22:25:33 +08:00
|
|
|
inode's i_atime field is used to store a checksum of the xattr value;
|
|
|
|
|
and i_ctime/i_version store a 64-bit reference count, which enables
|
2026-01-21 18:59:54 +08:00
|
|
|
sharing of large xattr values between multiple owning inodes. For
|
|
|
|
|
backward compatibility with older versions of this feature, the
|
2026-01-29 22:25:33 +08:00
|
|
|
i_mtime/i_generation *may* store a back-reference to the inode number
|
|
|
|
|
and i_generation of the **one** owning inode (in cases where the EA
|
2026-01-21 18:59:54 +08:00
|
|
|
inode is not referenced by multiple inodes) to verify that the EA inode
|
|
|
|
|
is the correct one being accessed.
|
