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Date: Wed, 15 Jul 2026 10:01:39 -0600
From: Keith Busch <kbusch@kernel.org>
To: Caleb Sander Mateos <csander@purestorage.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Sagi Grimberg <sagi@grimberg.me>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] nvme/core: advertise BLK_EXPECTED_REF_TAG_CAPABLE
Message-ID: <aleu49e4GxG-Z7B6@kbusch-mbp>
References: <20260627061933.2187447-1-csander@purestorage.com>
 <20260627061933.2187447-3-csander@purestorage.com>
 <20260714135310.GB714@lst.de>
 <CADUfDZoGheGP6JCwwV=BCBnqxAspJ1n9Aes=UsjtS-DxAMxeEA@mail.gmail.com>
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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 <hch@lst.de> 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.