Re: [RFC PATCH 2/2] nvme/core: advertise BLK_EXPECTED_REF_TAG_CAPABLE

On Wed, Jul 15, 2026 at 08:30:33AM -0700, Caleb Sander Mateos wrote:
> On Tue, Jul 14, 2026 at 6:53 AM Christoph Hellwig <[email protected]> wrote:
> >
> > For Type 2 this remapping could work, but doing it unconditionally
> > will make all data written using and earlier kernel in a partition
> > unreadable once this changes has been applied.
> 
> I mentioned this in the cover letter (and that's why I marked these
> patches "RFC"). Unless you have a clever idea, it does seem like an
> insurmountable obstacle here.

We had a similar problem when we enabled PI at the end of the metadata
rather than just at the beginning. This left machines unbootable after
upgrading the kernel, so we have a module parameter to turn off support
for the feature. It's an unpleasant solution as there's no upgrade path
to ever turn on the feature without a format first.