> Author: Theodore Ts'o <tytso@mit.edu>
> Date: Mon Dec 7 14:08:51 2009 -0500
>
> ext4: Use ext4 file system driver for ext2/ext3 file system mounts
>
> Add a new config option, CONFIG_EXT4_USE_FOR_EXT23 which if enabled,
> will cause ext4 to be used for either ext2 or ext3 file system mounts
> when ext2 or ext3 is not enabled in the configuration.
>
> This allows minimalist kernel fanatics to drop to file system drivers
> from their compiled kernel with out losing functionality.
>
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
>
>
> So now we have this thing, and people are using it, and running into trouble:
>
>
http://bugzilla.kernel.org/show_bug.cgi?id=15420
> Bug 15420 - EXT4_USE_FOR_EXT23 causes wrong free space calculation on ext2 and ext3
>
> and now we propose turning off delalloc if we mount ext3 as ext4; however,
> migrated ext3->ext4 filesystems, which initially may have no difference other
> than a superblock feature flag, will not get this behavior, I guess.
>
> Jan suggests that we not surprise users by having delalloc enabled when ext3
> is mounted with the ext4 driver. However there are other behavior differences
> as well, mballoc behavior comes to mind at least. What about the 32000 subdir
> limit? If we go back to ext3 is it ok with the subsecond timestamps and
> creation time etc? Maybe so... have we tested any of this?
