Re: [PATCH RFC fstests] generic: add a test for multigrain timestamps

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2026-10-28 at 08:54 -0700, Christoph Hellwig wrote:
> On Tue, Oct 27, 2026 at 09:58:50AM -0400, Jeff Layton wrote:
> > Ensure that the mtime and ctime apparently change, even when there are
> > multiple writes in quick succession. Since this is opt-in for in-kernel
> > filesystems and there is no way to test for this feature in userland,
> > limit it to just ext4, f2fs, btrfs, tmpfs and xfs for now.
> > 
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > I'd like to start testing this to make sure it doesn't break, but it's
> > not universally supported on all filesystems. Is an explicit allowlist
> > like this the right approach?
> 
> Can we please expose the fact that multi-grain timestamp are supported
> from the kernel?  This seems like it would be just one bit we'd need
> in sttx or something similar.

I'd been resisting that, but maybe it's a good idea. I'll see what I
can come up with. We can probably just add a flag to stx_attributes?
-- 
Jeff Layton <jlayton@kernel.org>