Re: [PATCH, RFC] Add new "development flag" to the ext4 filesystem

[Eric Sandeen <sandeen@redhat.com>]

Theodore Tso wrote:

> If we do that, then the only downside of having ext3 filesystems run
> under ext4 is the test matrix concern.  Since I'm still hoping that
> some point in the future, fs/ext4 could subsume fs/ext3 so we don't
> have to worry about bug fixes going into fs/ext2 AND fs/ext3 AND
> fs/ext4, I have my own reasons for wanting that.  But I do understand
> the concerns that maybe in the short term some distro's don't want to
> do that.  So in that case I could see adding a "you must have extents"
> test into ext4, if I distro has specific support concerns. But for
> people who are running mainline kernel, I think it's actually a *good*
> thing if fs/ext4 can mount and read and write to an ext3 filesystem
> --- as long as it doesn't automatically turn on features behind the
> user's back.

Well, sure, the ability of ext4 code to mount,read,write ext3
filesystems is fine, esp. if ext4.ko stops doing things which makes it
hard to go back to ext3.  And, I do like the long-term plan of ext4
replacing ext3, it's a bit of a pain to keep this all in sync.

I just think that ext4.ko running ext3 filesystems needs to be under
explicit control, and not something that happens, occasionally,
accidentally, without the user/administrator requesting it.  Least
surprise, and all that...

-Eric