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