Re: [Qemu-devel] virtio 1 issues

[Jason Wang <jasowang@redhat.com>]

On 08/07/2015 06:49 PM, Cornelia Huck wrote:
> On Fri, 07 Aug 2015 13:07:35 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
>>> 2. ring resizing is broken - it actually has a comment:
>>>         /* TODO: need a way to put num back on reset. */
>>> guest that runs out of memory might down-size the ring.
>>> Afterwards, ring size won't come back up after reset - not nice.
>>>
>> Then we need a new field to keep track the original queue size and
>> migrate this.
> virtio-ccw neatly sidesteps it by not implementing ring size changes at
> all :)
>
> But it isn't really all good, see
>
> /* TODO: Add interface to handle vring.num changing */
>
> We either need to implement this or fence off changing the ring size, I
> guess.

Yes.

>>> Given that the modern layout is disabled by default,
>>> I don't think these are release blockers.
>>>
>> Yes and looks like we need a new subsection and transport specific
>> callbacks to fix above?
> Agreed, it's not urgent as virtio-1 is not yet the default (and not
> even enabled for ccw).
>
> I'm not sure we need transport-specific callbacks. Shouldn't the core
> be able to track initial and actual size (and migrate in an optional
> subsection), as long as the transports use defined interfaces to
> interact with it?
>

For size, I agree it should be tracked by core. But we need also track
transport specific data like dfselect/gfselect for pci.