Documentation / filesystems / ext4 / eainode.rst

Based on kernel version 5.10.1. Page generated on 2020-12-14 21:14 EST.

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.. 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,
the EA\_INODE feature allows us to store the value in the data blocks of
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
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
sharing of large xattr values between multiple owning inodes. For
backward compatibility with older versions of this feature, the
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
inode is not referenced by multiple inodes) to verify that the EA inode
is the correct one being accessed.