1 .. SPDX-License-Identifier: GPL-2.0
6 ext4 reserves some inode for special features, as follows:
15 - Doesn't exist; there is no inode 0.
17 - List of defective blocks.
29 - Reserved group descriptors inode. (“resize inode”)
33 - The “exclude” inode, for snapshots(?)
35 - Replica inode, used for some non-upstream feature?
37 - Traditional first non-reserved inode. Usually this is the lost+found directory. See s\_first\_ino in the superblock.