Re: [Qemu-devel] [PATCH 2/5] virtio: Migrate the "start_on_kick" flag

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jun 03, 2019 at 10:16:39PM +0200, Greg Kurz wrote:
> On Wed, 29 May 2019 15:09:52 +0800
> elohimes@gmail.com wrote:
> 
> > From: Xie Yongji <xieyongji@baidu.com>
> > 
> > We should migrate the "start_on_kick" flag so that we
> > would not miss starting device on kicking at startup
> > after migration.
> > 
> 
> Hmm... IIUC "start_on_kick" means "virtio 1.0 transitional device that has
> not been started yet", ie:
> 
> !vdev->started &&
> (virtio_host_has_feature(vdev, VIRTIO_F_VERSION_1) &&
>  !virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1))

Or a legacy device I guess?

> If so, not sure why you need this extra field in the first place, but
> you probably don't need to migrate it. Just recalculate in a post load
> callback.
> 
> > Signed-off-by: Xie Yongji <xieyongji@baidu.com>
> > ---
> >  hw/virtio/virtio.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> > 
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index fc8fca81ad..4d4ff67791 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -1802,6 +1802,13 @@ static bool virtio_started_needed(void *opaque)
> >      return vdev->started;
> >  }
> >  
> > +static bool virtio_start_on_kick_needed(void *opaque)
> > +{
> > +    VirtIODevice *vdev = opaque;
> > +
> > +    return vdev->start_on_kick;
> > +}
> > +
> >  static const VMStateDescription vmstate_virtqueue = {
> >      .name = "virtqueue_state",
> >      .version_id = 1,
> > @@ -1941,6 +1948,17 @@ static const VMStateDescription vmstate_virtio_started = {
> >      }
> >  };
> >  
> > +static const VMStateDescription vmstate_virtio_start_on_kick = {
> > +    .name = "virtio/start_on_kick",
> > +    .version_id = 1,
> > +    .minimum_version_id = 1,
> > +    .needed = &virtio_start_on_kick_needed,
> > +    .fields = (VMStateField[]) {
> > +        VMSTATE_BOOL(start_on_kick, VirtIODevice),
> > +        VMSTATE_END_OF_LIST()
> > +    }
> > +};
> > +
> >  static const VMStateDescription vmstate_virtio = {
> >      .name = "virtio",
> >      .version_id = 1,
> > @@ -1957,6 +1975,7 @@ static const VMStateDescription vmstate_virtio = {
> >          &vmstate_virtio_broken,
> >          &vmstate_virtio_extra_state,
> >          &vmstate_virtio_started,
> > +        &vmstate_virtio_start_on_kick,
> >          NULL
> >      }
> >  };