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    SubjectRe: [PATCH v3 11/11] virtio: balloon: Add freeze, restore handlers to support S4
    On (Thu) 17 Nov 2011 [14:25:08], Michael S. Tsirkin wrote:
    > On Thu, Nov 17, 2011 at 05:27:42PM +0530, Amit Shah wrote:
    > > Delete the vqs on the freeze callback to prepare for hibernation.
    > > Re-create the vqs in the restore callback to resume normal function.
    > >
    > > Signed-off-by: Amit Shah <amit.shah@redhat.com>
    > > ---
    > > drivers/virtio/virtio_balloon.c | 20 ++++++++++++++++++++
    > > 1 files changed, 20 insertions(+), 0 deletions(-)
    > >
    > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
    > > index 1ff3cf4..90149d1 100644
    > > --- a/drivers/virtio/virtio_balloon.c
    > > +++ b/drivers/virtio/virtio_balloon.c
    > > @@ -363,6 +363,22 @@ static void __devexit virtballoon_remove(struct virtio_device *vdev)
    > > kfree(vb);
    > > }
    > >
    > > +#ifdef CONFIG_PM
    > > +static int virtballoon_freeze(struct virtio_device *vdev)
    > > +{
    > > + /* Now we reset the device so we can clean up the queues. */
    > > + vdev->config->reset(vdev);
    > > +
    >
    > This is a weird thing to do. We normally delete vqs then reset.

    No, all the drivers first reset, then delete.

    > For example, I don't know whether we guarantee what happens
    > to MSI-X vectors assigned meanwhile if you reset.
    > IIRC qemu doesn't use MSI-X for the balloon, but nothing
    > prevents it.
    >
    > > + vdev->config->del_vqs(vdev);
    >
    > What prevents requests being submitted at this point?
    > I see all kind of handling of freezing in the balloon thread ...
    > maybe that gives us some guarantees, but if yes
    > it makes sense to add a comment to point this out.

    Once reset, the host won't write anything to the vqs anyway..

    Amit


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