is there a way to tell that you have ext4 filesystem vs ext3

[Mike]

Eric Sandeen <sandeen <at> redhat.com> writes:

> Good question.  There's no consensus upstream to drop the "dev" from
> "ext4dev" yet, so it may remain as a boot option for this release, yet.
> 
> I think it may technically require a fedora "feature" change to to drop
> the boot argument at this point, but I'm not certain...
> 
> It certainly won't be switched in as the *default* for F10, though.

Ultimately when id does become default I wonder what the situation will be 
if you install clean for F11+ and make the / partition default formatted
to ext4, but there may be other pre-existing ext3 /opt or /home paritions that
have lots of files on which should not be formatted....

In that case is there a way to convert the ext3 to ext4 whilst retaining
all the pre-existing files?  If not then would the system be happy having
ext4 / partition as well as co-existing ext3 /opt and /home partitions on 
a single system?