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

Chaitanya Kulkarni
2022-12-13T04:58:55Z

Michael,

On 12/7/22 12:28, Michael S. Tsirkin wrote:
> On Wed, Dec 07, 2022 at 08:31:28AM -0800, Christoph Hellwig wrote:
>> On Wed, Dec 07, 2022 at 05:21:48AM -0500, Michael S. Tsirkin wrote:
>>> Christoph you acked the spec patch adding this to virtio blk:
>>>
>>> Still not a fan of the encoding, but at least it is properly documented
>>> now:
>>>
>>> Acked-by: Christoph Hellwig <hch@lst.de>
>>>
>>> Did you change your mind then? Or do you prefer a different encoding for
>>> the ioctl then? could you help sugesting what kind?
>>
>> Well, it is good enough documented for a spec. I don't think it is
>> a useful feature for Linux where virtio-blk is our minimum viable
>> paravirtualized block driver.
>
> No idea what this means, sorry. Now that's in the spec I expect (some)
> devices to implement it and if they do I see no reason not to expose the
> data to userspace.
>

Even if any device implements is it can always use passthru commands.
See below for more info...

> Alvaro could you pls explain the use-case? Christoph has doubts that
> it's useful. Do you have a device implementing this?
>

From what I know, virtio-blk should be kept minimal and should not
add any storage specific IOCTLs or features that will end up loosing
its generic nature.

The IOCTL we are trying to add is Flash storage specific which
goes against the nature of generic storage and makes it non-generic.
In case we approve this it will open the door for non-generic
code/IOCTL in the virtio-blk and that needs to be avoided.

For any storage specific features or IOCTL (flash/HDD) it should
be using it's own frontend such as virtio-scsi or e.g. nvme and
not virtio-blk.

Hope this helps.

-ck