[PATCH 1/1] kvm: qemu: virtio-net: migration fixes

[Mark McLoughlin <markmc@redhat.com>]

We were failing to save two important pieces of state:

  1) Whether the guest will supply us rx buffers using the
     new mergeable format; this caused the migrated guest
     to crash with "virtio-net header not in first element"

  2) Whether the tx/rx buffers we exchange with the tap
     code should include a virtio_net_hdr header; this
     caused the migrated guest to receive garbage packets
     because the tap code was stripping away the header
     and virtio_net was interpreting packet data as the
     virtio_net header

With these fixes a guest using mergeable rx buffers and
GSO passes a simple "ping while migrating" test.

The mergeable rx buffers part has been sent upstream to
qemu-devel, but the GSO part is KVM specific.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
---
 qemu/hw/virtio-net.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/qemu/hw/virtio-net.c b/qemu/hw/virtio-net.c
index ef8f591..e47a0a4 100644
--- a/qemu/hw/virtio-net.c
+++ b/qemu/hw/virtio-net.c
@@ -360,6 +360,11 @@ static void virtio_net_save(QEMUFile *f, void *opaque)
 
     qemu_put_buffer(f, n->mac, 6);
     qemu_put_be32(f, n->tx_timer_active);
+    qemu_put_be32(f, n->mergeable_rx_bufs);
+
+#ifdef TAP_VNET_HDR
+    qemu_put_be32(f, tap_has_vnet_hdr(n->vc->vlan->first_client));
+#endif
 }
 
 static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
@@ -373,6 +378,12 @@ static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
 
     qemu_get_buffer(f, n->mac, 6);
     n->tx_timer_active = qemu_get_be32(f);
+    n->mergeable_rx_bufs = qemu_get_be32(f);
+
+#ifdef TAP_VNET_HDR
+    if (qemu_get_be32(f))
+      tap_using_vnet_hdr(n->vc->vlan->first_client, 1);
+#endif
 
     if (n->tx_timer_active) {
         qemu_mod_timer(n->tx_timer,
-- 
1.6.0.6