Re: [PATCH 05/21] virtio: modify save/load handler to handle inuse varialble.

Michael S. Tsirkin
2010-11-28T11:47:14Z

On Sun, Nov 28, 2010 at 08:27:58PM +0900, Yoshiaki Tamura wrote:
> 2010/11/28 Michael S. Tsirkin <mst@redhat.com>:
> > On Thu, Nov 25, 2010 at 03:06:44PM +0900, Yoshiaki Tamura wrote:
> >> Modify inuse type to uint16_t, let save/load to handle, and revert
> >> last_avail_idx with inuse if there are outstanding emulation.
> >>
> >> Signed-off-by: Yoshiaki Tamura <tamura.yoshiaki@lab.ntt.co.jp>
> >
> > This changes migration format, so it will break compatibility with
> > existing drivers. More generally, I think migrating internal
> > state that is not guest visible is always a mistake
> > as it ties migration format to an internal implementation
> > (yes, I know we do this sometimes, but we should at least
> > try not to add such cases).  I think the right thing to do in this case
> > is to flush outstanding
> > work when vm is stopped.  Then, we are guaranteed that inuse is 0.
> > I sent patches that do this for virtio net and block.
>
> Could you give me the link of your patches? I'd like to test
> whether they work with Kemari upon failover. If they do, I'm
> happy to drop this patch.
>
> Yoshi

Look for this:
stable migration image on a stopped vm
sent on:
Wed, 24 Nov 2010 17:52:49 +0200

> >
> >> ---
> >>  hw/virtio.c |    8 +++++++-
> >>  1 files changed, 7 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/hw/virtio.c b/hw/virtio.c
> >> index 849a60f..5509644 100644
> >> --- a/hw/virtio.c
> >> +++ b/hw/virtio.c
> >> @@ -72,7 +72,7 @@ struct VirtQueue
> >>      VRing vring;
> >>      target_phys_addr_t pa;
> >>      uint16_t last_avail_idx;
> >> -    int inuse;
> >> +    uint16_t inuse;
> >>      uint16_t vector;
> >>      void (*handle_output)(VirtIODevice *vdev, VirtQueue *vq);
> >>      VirtIODevice *vdev;
> >> @@ -671,6 +671,7 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f)
> >>          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);
> >> +        qemu_put_be16s(f, &vdev->vq[i].inuse);
> >>          if (vdev->binding->save_queue)
> >>              vdev->binding->save_queue(vdev->binding_opaque, i, f);
> >>      }
> >> @@ -711,6 +712,11 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f)
> >>          vdev->vq[i].vring.num = qemu_get_be32(f);
> >>          vdev->vq[i].pa = qemu_get_be64(f);
> >>          qemu_get_be16s(f, &vdev->vq[i].last_avail_idx);
> >> +        qemu_get_be16s(f, &vdev->vq[i].inuse);
> >> +
> >> +        /* revert last_avail_idx if there are outstanding emulation. */
> >> +        vdev->vq[i].last_avail_idx -= vdev->vq[i].inuse;
> >> +        vdev->vq[i].inuse = 0;
> >>
> >>          if (vdev->vq[i].pa) {
> >>              virtqueue_init(&vdev->vq[i]);
> >> --
> >> 1.7.1.2
> >>
> >> --
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