How to: determine if it's ext3 or ext2 mounted as ext4?

[Michael Tokarev <mjt@tls.msk.ru>]

Hello.

I'm performing conversion from ext3 to ext4 currently,
on several nodes.  The current plan is to remount them
as ext4 first, next use tune2fs to update list of
filesystem features, next to remount them again in order
to actually turn the features on.

The question is: what's the way to determine if the
actual features used corresponds to ext3 or ext4?  Or,
in other words, if the last step in the above sequence
has been completed or not?

The filesystem superblock at this time will show ext4
already (since ext4-specific features are turned on),
but actual features used will be ext3.

Is there a way to determine if a remount is still needed?

Besides, when I first use tune2fs (on a ext3-mounted fs)
and next remount it, the filesystem wants an fsck pass,
which finds checksum errors on all newly written files,
and these errors can't be corrected automatically at boot
if -y fsck flag is NOT used (default on Debian).  So I
had to remount them first and convert second.

Thanks!

/mjt