Bug#731072: linux-image-3.11-2-amd64: Mounting of small ext2 file systems fails on 3.11
Package: src:linux
Version: 3.11.8-1
Severity: normal
Dear Maintainer,
due to the changed kernel configuration to disable the ext2 module and
to enable
CONFIG_EXT4_USE_FOR_EXT23=y
the support for small ext2 file systems has been (accidently?) removed.
Small file systems here are file systems with less than 1024 blocks,
i.e. less than 1 to 4 MeBi depending on the block size. The change has
been introduced between 3.10 and 3.11 in Debian.
When trying to mount such a file system, the following error is printed:
> mount: wrong fs type, bad option, bad superblock on /dev/loop0,
> missing codepage or helper program, or other error
> In some cases useful info is found in syslog - try
> dmesg | tail or so
The syslog contains the following line
> EXT4-fs (loop0): bad geometry: block count 1440 exceeds size of device (1048 blocks)
This information is not helpful. While the loss of support for small file
systems is unfortunate, I think the lack of information here is unacceptable.
Such small file systems are still being used, e.g. on removable media or in
the embedded world, thus the bug's severity can be critical for some users.
I do not exactly know what the best fix of this bug is (and thus where to
assign this bug), but some solutions are:
- Revert the kernel configuration to support the ext2 module again
- Print a warning during kernel upgrade
- Print a precise error when mounting fails
- Support such small file systems with the ext4-for-ext2 config
For everyone else who is hit by this problem: As a workaround, an old Debian
kernel (3.10 or older) or a self-compiled kernel with separate ext2 support
can be used to recover the data on such file systems.
> mkfs.ext4 -b 1024 DEVICE
can be used to create an ext4 file system with a minimum size of 1 MeBi as an
alternative.
Cheers
Patrick
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