Re: [virtio-dev] Backend libraries for VirtIO device emulation

[Jan Kiszka <jan.kiszka@siemens.com>]

On 06.03.20 21:24, Alex BennÃe wrote:
> I suspect all of these multi-process models just hand wave away details
> like migration because that really does benefit from a single process
> with total awareness of the state of the system. That said I wonder how
> robust a guest can be if the device emulation may go away at any time?
>
> I guess in virtio if you never signal the consumption of a virt-queue it
> will still be there waiting until you restart the emulation process and
> pick up from where you left off?

The virtio spec seems be fine with individual backends dying. Recovery 
depends on the hypervisor maintaining state for the backends - not sure 
if that is easily doable, though.

But the challenge starts earlier: virtio-over-ivshmem is designed to 
support independent backends lifecycles (and has no state except for 
guest lifeness in the hypervisor). But while playing with that, I 
immediately ran into Linux frontend code assuming that a virtio device 
never dies (virtio console, IIRC). I suspect that there are more cases 
in Linux, not to speak of other guests.

Jan

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