On Mon, Aug 31, 2015 at 3:31 PM, Raymond Jennings [off-list ref] wrote:

That said, I wouldn't mind myself if the ext4 driver were given a very
grueling regression test to make sure it can actually handle old ext3
systems as well as the ext3 driver can.

That's not my only worry. Things like "can you go back to ext3-only"
is an issue too - I don't think that's been a big priority for ext4
any more, and if there are any existing hold-outs that still use ext3,
they may want to be able to go back to old kernels.

So it's not just a "you can use ext4 instead" issue. Can you do that
*without* then forcing an upgrade forever on that partition? I'm not
sure the ext4 people are really even willing to guarantee that kind of
backwards compatibility.

I could be ok with removing ext3 in theory, but I haven't seen a lot
of rationale for it, and I don't know if there are still users who may
have their own good reasons to stay with ext3. Maybe there has been
lots of discussion about this on fsdevel (which I don't follow), and
I'm just lacking the background, but if so I want to see that
background. Not just a oneliner description that basically says
"remove ext3 support".

                    Linus