[RFC PATCH 18/18] virtio_net: register incremental migration handlers

["Eugenio Pérez" <eperezma@redhat.com>]

This way VirtIONet can detect when the incoming migration starts.

While registering in the backend (nc->peer) seems more logical, we need
nic dma address space, and we cannot get it from the backend.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
This could be done in vhost_vdpa or VirtIODevice struct, but future
series will add state restore through CVQ so it's easier to start in
VirtIONEt directly.  If we need to make this more generic, we can move
to VirtIODevice and expose callbacks from VirtIONet class.

Also, the pointer may not be the best id, but there are not a lot of
things initialized in n.
---
 hw/net/virtio-net.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 29e33ea5ed..470338fa7c 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -38,6 +38,7 @@
 #include "qapi/qapi-events-migration.h"
 #include "hw/virtio/virtio-access.h"
 #include "migration/misc.h"
+#include "migration/register.h"
 #include "standard-headers/linux/ethtool.h"
 #include "sysemu/sysemu.h"
 #include "trace.h"
@@ -3808,9 +3809,27 @@ static void virtio_net_device_unrealize(DeviceState *dev)
     virtio_cleanup(vdev);
 }
 
+static int virtio_net_load_setup(QEMUFile *f, void *opaque)
+{
+    VirtIONet *n = opaque;
+    NetClientState *nc = qemu_get_subqueue(n->nic, 0);
+
+    if (nc->peer->info->load_setup) {
+        return nc->peer->info->load_setup(nc->peer, n->nic);
+    }
+
+    return 0;
+}
+
+static const SaveVMHandlers savevm_virtio_net_handlers = {
+    .load_setup = virtio_net_load_setup,
+};
+
+
 static void virtio_net_instance_init(Object *obj)
 {
     VirtIONet *n = VIRTIO_NET(obj);
+    g_autoptr(GString) id = g_string_new(NULL);
 
     /*
      * The default config_size is sizeof(struct virtio_net_config).
@@ -3822,6 +3841,10 @@ static void virtio_net_instance_init(Object *obj)
                                   DEVICE(n));
 
     ebpf_rss_init(&n->ebpf_rss);
+
+    g_string_printf(id, "%p", n);
+    register_savevm_live(id->str, VMSTATE_INSTANCE_ID_ANY, 1,
+                         &savevm_virtio_net_handlers, n);
 }
 
 static int virtio_net_pre_save(void *opaque)
-- 
2.39.3