linux/Documentation/filesystems/ext4/eainode.rst
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   1.. SPDX-License-Identifier: GPL-2.0
   2
   3Large Extended Attribute Values
   4-------------------------------
   5
   6To enable ext4 to store extended attribute values that do not fit in the
   7inode or in the single extended attribute block attached to an inode,
   8the EA\_INODE feature allows us to store the value in the data blocks of
   9a regular file inode. This “EA inode” is linked only from the extended
  10attribute name index and must not appear in a directory entry. The
  11inode's i\_atime field is used to store a checksum of the xattr value;
  12and i\_ctime/i\_version store a 64-bit reference count, which enables
  13sharing of large xattr values between multiple owning inodes. For
  14backward compatibility with older versions of this feature, the
  15i\_mtime/i\_generation *may* store a back-reference to the inode number
  16and i\_generation of the **one** owning inode (in cases where the EA
  17inode is not referenced by multiple inodes) to verify that the EA inode
  18is the correct one being accessed.
  19