Re: [PATCH v3 11/11] virtio: balloon: Add freeze, restore handlers to support S4

Michael S. Tsirkin
2011-11-17T12:23:44Z

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.
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.

> + return 0;
> +}
> +
> +static int virtballoon_restore(struct virtio_device *vdev)
> +{
> + return init_vqs(vdev->priv);
> +}
> +#endif
> +
> static unsigned int features[] = {
> VIRTIO_BALLOON_F_MUST_TELL_HOST,
> VIRTIO_BALLOON_F_STATS_VQ,
> @@ -377,6 +393,10 @@ static struct virtio_driver virtio_balloon_driver = {
> .probe = virtballoon_probe,
> .remove = __devexit_p(virtballoon_remove),
> .config_changed = virtballoon_changed,
> +#ifdef CONFIG_PM
> + .freeze = virtballoon_freeze,
> + .restore = virtballoon_restore,
> +#endif
> };
>
> static int __init init(void)
> --
> 1.7.7.1