Re: [PATCH v3] virtio_blk: add VIRTIO_BLK_F_LIFETIME feature support

From: Jens Axboe <axboe@kernel.dk>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-scsi@vger.kernel.org, linux-nvme@lists.infradead.org,
	virtualization@lists.linux-foundation.org,
	linux-block@vger.kernel.org, dm-devel@redhat.com,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Enrico Granata <egranata@google.com>
Subject: Re: [PATCH v3] virtio_blk: add VIRTIO_BLK_F_LIFETIME feature support
Date: Mon, 5 Dec 2022 13:36:25 -0700	[thread overview]
Message-ID: <c062d9cb-e8c6-543a-88be-016973058d43@kernel.dk> (raw)
In-Reply-To: <20221205152708-mutt-send-email-mst@kernel.org>

On 12/5/22 1:29?PM, Michael S. Tsirkin wrote:
> On Mon, Dec 05, 2022 at 11:53:51AM -0700, Jens Axboe wrote:
>> On 12/5/22 11:36?AM, Alvaro Karsz wrote:
>>> Hi,
>>>
>>>> Is this based on some spec? Because it looks pretty odd to me. There
>>>> can be a pretty wide range of two/three/etc level cells with wildly
>>>> different ranges of durability. And there's really not a lot of slc
>>>> for generic devices these days, if any.
>>>
>>> Yes, this is based on the virtio spec
>>> https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html
>>> section  5.2.6
>>
>> And where did this come from?
> 
> 
> Here's the commit log from the spec:
> 	In many embedded systems, virtio-blk implementations are
> 	backed by eMMC or UFS storage devices, which are subject to
> 	predictable and measurable wear over time due to repeated write
> 	cycles.
> 
> 	For such systems, it can be important to be able to track
> 	accurately the amount of wear imposed on the storage over
> 	time and surface it to applications. In a native deployments
> 	this is generally handled by the physical block device driver
> 	but no such provision is made in virtio-blk to expose these
> 	metrics for devices where it makes sense to do so.
> 
> 	This patch adds support to virtio-blk for lifetime and wear
> 	metrics to be exposed to the guest when a deployment of
> 	virtio-blk is done over compatible eMMC or UFS storage.
> 
> 	Signed-off-by: Enrico Granata <egranata@google.com>
> 
> Cc Enrico Granata as well.

Alvaro sent me this one privately too. To be honest, I don't like this
patch very much, but that's mostly because the spec for this caters to a
narrow use case of embedded flash. It's not a generic storage thing,
it's just for mmc/ufs and the embedded space. That's a missed
opportunity. And either it'll become mostly unused, or it'll actually be
used and then extended at some point.

While I'm not a fan at all, if you guys are willing to take it in
virtio-blk, then I won't stand in your way. I would rename it though to
more specifically detail what it deals with.

-- 
Jens Axboe
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