linux-kernel - Re: [PATCH] virtio_blk: Add support for lifetime feature

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Date:   Thu, 15 Apr 2021 16:57:51 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Stefan Hajnoczi <stefanha@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Enrico Granata <egranata@...gle.com>, mst@...hat.com,
        jasowang@...hat.com, pbonzini@...hat.com, axboe@...nel.dk,
        virtualization@...ts.linux-foundation.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_blk: Add support for lifetime feature

On Wed, Apr 14, 2021 at 09:44:35AM +0100, Stefan Hajnoczi wrote:
> On Mon, Apr 12, 2021 at 10:42:17AM +0100, Christoph Hellwig wrote:
> > A note to the virtio committee:  eMMC is the worst of all the currently
> > active storage standards by a large margin.  It defines very strange
> > ad-hoc interfaces that expose very specific internals and often provides
> > very poor abstractions.  It would be great it you could reach out to the
> > wider storage community before taking bad ideas from the eMMC standard
> > and putting it into virtio.
> 
> As Michael mentioned, there is still time to change the virtio-blk spec
> since this feature hasn't been released yet.
> 
> Why exactly is exposing eMMC-style lifetime information problematic?
> 
> Can you and Enrico discuss the use case to figure out an alternative
> interface?

Mostly because it exposed a very awkward encoding that is not actually
documented in any publically available spec.

If you want to incorporate a more open definition doing something
like the NVMe 'Endurance Estimate' and 'Percentage Used' fields.  But
the most important thing is to fully document the semantics in the
virtio document instead of refercing a closed standard.