On Sun, 27 Dec 2020 05:00:05 -0500
"Michael S. Tsirkin" <> wrote:
> On Fri, Dec 25, 2020 at 08:38:35AM +0100, Halil Pasic wrote:
> >When driver is trying to set DEVICE_STOPPED, the device MUST not
> >process new avail requests and MUST complete all requests that is
> >currently processing before setting DEVICE_STOPPED.
>
> ...
>
> > Since we have a synchronous API setting DEVICE_STOPPED would also have to
> > block until all in-flight requests are completed.
>
> Judging from the surrounding discussion,
> when you say complete you seem to mean "use", and
My intention was merely to paraphrase Jason's proposal which says:
+When driver is trying to set DEVICE_STOPPED, the device MUST not
+process new avail requests and MUST complete all requests that is
+currently processing before setting DEVICE_STOPPED.
> I'm not sure how you define in flight, but
> it seems there could be many of these (up to a full queue?)
In the follow-on discussion 'in-flight' emerged as an alternative to
'all requests that is currently processing' form the proposed text.
A large part of the discussion is, IMHO, about finding precise
definitions, for what the quoted paragraph is trying to express.
> so waiting for all available buffers to be
> used might indeed require an asynchronous interface,
> which gets complex very quickly.
>
> However wouldn't it be possible for device to just cancel
> processing available buffers even if it started processing
> them? Some buffers could be in indeterminate state
> (e.g. we might not have a way to know how much data did
> device have time to write into a buffer).
>
Maybe Jason can answer this one.
> Making it clearer what does "complete" mean here might help.
>
I think what we are trying to accomplish here, is avoiding, having
non-standardised state in device (that can not be dropped) when
migrating.
I'm still struggling with wrapping my mind around the problem. AFAIU
migration and migratability is not really a feature of the virtio
standard, but can be a feature of it's implementation
(e.g. QEMU & KVM), where the standard does help a great deal by having
certain aspects of the operation and interaction nailed down.
Regards,
Halil
