On 22.03.2023 12:09, Qu Wenruo wrote:
Hi,
Recently I observed newer mkfs.ext4 seems to create a new orphan inode
12, with some file extents.
Which seems to have no direct parent directory, thus tools like
btrfs-convert would also follow the ext4 inodes by creating an orphan
inode too.
On the other hand, if I go mkfs.ext3, the mysterious inode seems to be gone.
Is this inode 12 a known special inode?
This is orphan file. It is normal file; mke2fs creates first normal
inode for lost+found (11) and if enabled creates orphan file next which
gets next inode number (12). Inode number is recorded in superblock as
s_orphan_file_num.
/*27c*/ __le16 s_encoding; /* Filename charset encoding */
__le16 s_encoding_flags; /* Filename charset encoding
flags */
__le32 s_orphan_file_inum; /* Inode for tracking orphan
inodes */
If so, how can we avoid such special inode?
(s_special_ino is still 11, thus checking against that value doesn't
seem to help).
Some details of btrfs-convert:
It goes with ext2fs_open_inode_scan() to iterate all inodes of an ext4.
And if we hit an directory inode, we iterate the directory by using
ext2fs_dir_iterate2() to insert the dir entries between parent and child
inodes.
So if we hit an inode without any parent dir, an equivalent btrfs inode
would still be created, but btrfs-check would complain about such orphan
inode.
Thanks,
Qu
