Re: A new special orphan inode 12 in ext4 only?

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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




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