On Wed, Dec 05, 2012 at 01:08:07PM +0200, Michael S. Tsirkin wrote: > Add sanity check to address the following concern: > > On Wed, Dec 05, 2012 at 09:47:22AM +1030, Rusty Russell wrote: > > All we need is the index of the request; the rest can be re-read from > > the ring. > > I'd like to point out that this is not generally > true if any available requests are outstanding. > Imagine a ring of size 4. > Below A means available U means used. > > A 1 > A 2 > U 2 > A 2 > U 2 > A 2 > U 2 > A 2 > U 2 > > At this point available ring has wrapped around, the only > way to know head 1 is outstanding is because backend > has stored this info somewhere. > > The reason we manage to migrate without tracking this in migration > state is because we flush outstanding requests before > migration. > This flush is device-specific though, let's add > a safeguard in virtio core to ensure it's done properly. > > Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
Doh sent a wrong patch sorry. I'll resend the right one shortly. Pls disregard. > --- > > diff --git a/hw/virtio.c b/hw/virtio.c > index f40a8c5..b80a5a9 100644 > --- a/hw/virtio.c > +++ b/hw/virtio.c > @@ -788,6 +788,8 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f) > if (vdev->vq[i].vring.num == 0) > break; > > + assert(!vq->inuse); > + > qemu_put_be32(f, vdev->vq[i].vring.num); > qemu_put_be64(f, vdev->vq[i].pa); > qemu_put_be16s(f, &vdev->vq[i].last_avail_idx); > > -- > MST
