| Darrick J. Wong | c09f3ba | 2018-07-29 15:38:00 -0400 | [diff] [blame] | 1 | .. SPDX-License-Identifier: GPL-2.0 |
| 2 | |
| 3 | Large Extended Attribute Values |
| 4 | ------------------------------- |
| 5 | |
| 6 | To enable ext4 to store extended attribute values that do not fit in the |
| 7 | inode or in the single extended attribute block attached to an inode, |
| 8 | the EA\_INODE feature allows us to store the value in the data blocks of |
| 9 | a regular file inode. This “EA inode” is linked only from the extended |
| 10 | attribute name index and must not appear in a directory entry. The |
| 11 | inode's i\_atime field is used to store a checksum of the xattr value; |
| 12 | and i\_ctime/i\_version store a 64-bit reference count, which enables |
| 13 | sharing of large xattr values between multiple owning inodes. For |
| 14 | backward compatibility with older versions of this feature, the |
| 15 | i\_mtime/i\_generation *may* store a back-reference to the inode number |
| 16 | and i\_generation of the **one** owning inode (in cases where the EA |
| 17 | inode is not referenced by multiple inodes) to verify that the EA inode |
| 18 | is the correct one being accessed. |