Re: [virtio-comment] [PATCH V2 2/2] virtio: introduce STOP status bit

[Cornelia Huck <cohuck@redhat.com>]

On Tue, Jul 20 2021, Stefan Hajnoczi <stefanha@redhat.com> wrote:

> On Tue, Jul 20, 2021 at 11:04:55AM +0800, Jason Wang wrote:
>> Let me clarify, I agree we can't have a standard device state for all kinds
>> of device.
>> 
>> That's way I tend to leave them to be device specific. (but not
>> implementation specific)
>
> Unfortunately device state is sometimes implementation-specific. Not
> because the device is proprietary, but because the actual state is
> meaningless to other implementations.
>
> I mentioned virtiofs as an example where file system backends can be
> implemented in completely different ways so the device state cannot be
> migrated between implementations.
>
>> But we can generalize the virtqueue state for sure.
>
> I agree and also that some device types can standardize their device
> state representations. But I think it's a technical requirement to
> support implementation-specific state for device types where
> cross-implementation migration is not possible.
>
> I'm not saying the implementation-specific state representation has to
> be a binary blob. There could be an identifier registry to ensure live
> migration compatibility checks can be performed. There could also be a
> standard binary encoding for migration data. But the contents will be
> implementation-specific for some devices.

Can we at least put those implementation-specific states into some kind
of structured, standardized form? E.g. something like

<type category: file system backend data>
<type identifier: file system foo>
<length>
<data>

so that we can at least do compat checks for "I know how to handle foo"?


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