Re: remove _supported_fs

["Theodore Ts'o" <tytso@mit.edu>]

On Tue, Dec 10, 2024 at 05:08:27PM +0100, Christoph Hellwig wrote:
> I think the diffstat alone makes it pretty clear that moving away
> form that is a benefit, and it's also a lot easier to understand than
> that ext2 and ext3 magically run ext4 tests.

We talked about this on the weekly ext4 video chat, and I think what
we'd think is actually cleaner is to have a single directory for all
ext2/ext3/ext4 tests, and then eventually, have feature-specific
guards which skip a test if a particular feature isn't supported by a
particular file system.

It's always been my position that ext2, ext3, and ext4 are effectively
the same file system from a conceptual perspective, with multiple
implementations that support different subsets of file system
features.  This includes /usr/src/linux/fs/ext2,
/usr/src/linux/fs/ext3 (before we removed it from more recent
rernels), /usr/src/linux/fs/ext4, HURD's implementation of ext2,
NetBSD/FreeBSD's implementation of ext2, etc.

So effectively, what I'm proposing is that we use xfstests/tests/ext4
effectively as "extN", which would be used when testing with
FSTYP=ext[234].

Yes, we'll need to do some cleanup to add feature guards (e.g.,
_require_metadata_journaling, and "_require_scratch_ext4_feature mmp")
instead of _exclude_fs ext2, but in the end, I think this will be
cleaner and easier to understand since we'll know exactly what the
test is testing.

Cheers,

						- Ted