linux-ext4 - [BUG] e2fsprogs: mke2fs -S and e2fsck cannot recover on ext4

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Date:	Thu, 27 Oct 2011 16:13:16 +0900
From:	Akira Fujita <a-fujita@...jp.nec.com>
To:	Theodore Tso <tytso@....edu>, adilger.kernel@...ger.ca
CC:	ext4 development <linux-ext4@...r.kernel.org>
Subject: [BUG] e2fsprogs: mke2fs -S and e2fsck cannot recover on ext4

Hi,

If all of the superblock and backup superblocks are corrupted,
mke2fs -S which reinitializes the superblock and
group descriptors only is a last resort to recover.

However, on ext4, all of the files are lost with this way.
Because mke2fs -S for ext4 sets uninit_bg and then later e2fsck regards
all of block group as uninitialized one so that it can not recover
with bitmaps.

Of course ext3 can recover all of the files with mke2fsk -S,
ext4 should be able to recover as well.
There is a avoidance (see #3 of the reproduce steps)
but an appropriate fix would be needed for e2fsck.

* Reproduce steps and log are as follows:
  My e2fprogs was e2fsprogs-1.42-WIP

1. mkfe2s -t ext4 /dev/sdaX
2. create some files on ext4
3. mkfe2s -t ext4 -S -b 4096 /dev/sdaX　
    # This problem does not occur,
    # when we remove uninit_bg feature flag (-O ^uninit_bg).
4. e2fsck /dev/sdaX

e2fsck 1.42-WIP (16-Oct-2011)
Backing up journal inode block information.

/dev/sda8 contains a file system with errors, check forced.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Root inode not allocated.  Allocate<y>? yes

/lost+found not found.  Create<y>? yes

Pass 4: Checking reference counts
Pass 5: Checking group summary information
Block bitmap differences:  -(8483--8486) -(33026--33027)
Fix<y>? yes

Free blocks count wrong for group #0 (24286, counted=24285).
Fix<y>? yes

Free blocks count wrong (1030071, counted=1030070).
Fix<y>? yes

Free inodes count wrong for group #0 (8191, counted=8190).
Fix<y>? yes

Directories count wrong for group #0 (1, counted=2).
Fix<y>? yes

Free inodes count wrong (262143, counted=262142).
Fix<y>? yes

/dev/sda8: ***** FILE SYSTEM WAS MODIFIED *****
/dev/sda8: 2/262144 files (0.0% non-contiguous), 18506/1048576 blocks

As I reported before, e2fsck -b also can not recover with
backup superblock correctly.
# http://marc.info/?l=linux-ext4&m=131541543931429&w=2

Is there any ideas to fix these issues?

Regards,
Akira Fujita
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