Re: [RFC v2 08/14] virtio-net: detect VirtIONet status mid-migration change

[Eugenio Perez Martin <eperezma@redhat.com>]

On Fri, Mar 20, 2026 at 3:21 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
>
> Save VirtIONet's status field during early migration and compare it
> again during stop-and-copy.
>
> VirtIONet keeps its own status bits here, including VIRTIO_NET_S_LINK_UP
> and VIRTIO_NET_S_ANNOUNCE.
>

These are particular to the device, so we don't need to migrate them.
If any, we should check if the destination device changed the link
state so we can update the guest, but we don't do that as far as I
know.

> Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> ---
>  hw/net/virtio-net.c            | 6 ++++++
>  include/hw/virtio/virtio-net.h | 2 ++
>  2 files changed, 8 insertions(+)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 2dd130777e..88ce33b1d2 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -3872,6 +3872,7 @@ static int virtio_net_early_pre_save(void *opaque)
>      VirtIONetMigration *vnet_mig = n->migration;
>
>      vdev_mig->status_early = vdev->status;
> +    vnet_mig->status_early = n->status;
>
>      /* VirtIODevice config buffer snapshot */
>      g_free(vdev_mig->config_early);
> @@ -4304,6 +4305,11 @@ static bool virtio_net_has_delta(VirtIONet *n, VirtIODevice *vdev)
>          return true;
>      }
>
> +    /* Has the VirtIONet's status changed? */
> +    if (n->status != vnet_mig->status_early) {
> +        return true;
> +    }
> +
>      /* Has the VirtIONet's MAC info changed? */
>      if (memcmp(n->mac, vnet_mig->mac_early, ETH_ALEN) != 0) {
>          return true;
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index 1e1f1a3995..59345f1811 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -169,6 +169,7 @@ typedef struct VirtIONetQueue {
>
>  /**
>   * struct VirtIONetMigration - VirtIONet migration structure
> + * @status_early: VirtIONet status snapshot.
>   * @mac_early: MAC address early migration snapshot.
>   * @mtable_in_use_early: In-use MAC table entries.
>   * @mtable_uni_overflow_early: Unicast overflow MAC table entries.
> @@ -176,6 +177,7 @@ typedef struct VirtIONetQueue {
>   * @mtable_macs_early: MAC table entries.
>   */
>  typedef struct VirtIONetMigration {
> +    uint16_t status_early;
>      uint8_t mac_early[ETH_ALEN];
>      uint32_t mtable_in_use_early;
>      uint8_t mtable_uni_overflow_early;
> --
> 2.51.0
>