[RFC v2 05/14] virtio-net: detect VirtIODevice config buffer mid-migration change

[Jonah Palmer <jonah.palmer@oracle.com>]

This patch saves the config buffer and its length of a virtio-net
device's VirtIODevice to compare with later during the stop-and-copy
phase.

Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
---
 hw/net/virtio-net.c        | 21 +++++++++++++++++++++
 include/hw/virtio/virtio.h |  4 ++++
 2 files changed, 25 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 2733e0130c..ca4385df1a 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -3871,6 +3871,15 @@ static int virtio_net_early_pre_save(void *opaque)
     VirtIODevMigration *vdev_mig = vdev->migration;
 
     vdev_mig->status_early = vdev->status;
+
+    /* VirtIODevice config buffer snapshot */
+    g_free(vdev_mig->config_early);
+    vdev_mig->config_len_early = vdev->config_len;
+    if (vdev->config_len) {
+        vdev_mig->config_early = g_memdup2(vdev->config, vdev->config_len);
+    } else {
+        vdev_mig->config_early = NULL;
+    }
     return 0;
 }
 
@@ -4150,6 +4159,9 @@ static void virtio_net_device_unrealize(DeviceState *dev)
     virtio_cleanup(vdev);
 
     if (n->early_mig) {
+        g_free(vdev->migration->config_early);
+        vdev->migration->config_early = NULL;
+
         g_free(vdev->migration);
         vdev->migration = NULL;
 
@@ -4251,6 +4263,15 @@ static bool virtio_net_has_delta(VirtIONet *n, VirtIODevice *vdev)
         return true;
     }
 
+    /* Has the VirtIODevice's config buffer changed? */
+    if (vdev->config_len != vdev_mig->config_len_early) {
+        return true;
+    }
+    if (vdev->config_len && memcmp(vdev->config, vdev_mig->config_early,
+                                   vdev->config_len) != 0) {
+        return true;
+    }
+
     /*
      * Always return true for now until we're able to detect all possible
      * changes to a VirtIONet device.
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 752c46ce53..9949b94b64 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -103,10 +103,14 @@ enum virtio_device_endian {
  * struct VirtIODevMigration - Common VirtIODevice migration structure
  * @early_load: Flag to indicate an early virtio_load for the device.
  * @status_early: Device status at the time it was sent early.
+ * @config_len_early: Length of the config buffer at the time it was sent early.
+ * @config_early: Config buffer at the time it was sent early.
  */
 typedef struct VirtIODevMigration {
     bool early_load;
     uint8_t status_early;
+    size_t config_len_early;
+    uint8_t *config_early;
 } VirtIODevMigration;
 
 /**
-- 
2.51.0