On Wed, Feb 02, 2022 at 02:21:37PM +0100, Eric Auger wrote:
> >>> diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
> >>> index ec02029bb6..a112428c65 100644
> >>> --- a/hw/virtio/virtio-iommu.c
> >>> +++ b/hw/virtio/virtio-iommu.c
> >>> @@ -43,6 +43,7 @@
> >>>
> >>> typedef struct VirtIOIOMMUDomain {
> >>> uint32_t id;
> >>> + bool bypass;
> >> I am afraid this will break the migration if you don't change
> >> vmstate_domain.
> >>
> >> See static const VMStateDescription vmstate_domain.
> >> Also you need to migrate the new bypass field.
> >>
> >> Logically we should handle this with a vmstate subsection I think to
> >> handle migration of older devices. However I doubt the device has been
> >> used in production environment supporting migration so my guess is we
> >> may skip that burden and just add the missing field. Adding Juan, Dave &
> >> Peter for advices.
> > I'm not sure about users of this; if no one has used it then yeh; you
> > could bump up the version_id to make it a bit clearer.
>
> Thank you for your input. Yes to me it sounds OK to only bump the
> version_id while adding the new field.
Ok. Just to make sure we're on the same page, this means we don't support
migration from new->old or old->new instances, since the migration stream
doesn't carry a version ID for the virtio-iommu-device and domain
vmstates, as far as I understand. I also believe backward-incompatible
changes are fine this time around, though I don't have much visibility in
what's being used.
Thanks,
Jean
