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

[Michael S. Tsirkin]

On Mon, Jun 03, 2019 at 11:25:23PM +0200, Greg Kurz wrote:
> On Mon, 3 Jun 2019 17:03:06 -0400
> "Michael S. Tsirkin" <address@hidden> wrote:
> 
> > On Mon, Jun 03, 2019 at 10:16:39PM +0200, Greg Kurz wrote:
> > > On Wed, 29 May 2019 15:09:52 +0800
> > > address@hidden wrote:
> > >   
> > > > From: Xie Yongji <address@hidden>
> > > > 
> > > > 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?
> > 
> 
> Do you mean "start_on_kick" should be set for both legacy
> and virtio 1.0 transitional devices ?

Yes - generally when virtio 1 feature has not
been negotiated.

> > > 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 <address@hidden>
> > > > ---
> > > >  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
> > > >      }
> > > >  };