virtio-gpu: block migration of VMs with blob=true

"blob" resources don't have an associated pixman image:

#0  pixman_image_get_stride (image=0x0) at ../pixman/pixman-image.c:921
#1  0x0000562327c25236 in virtio_gpu_save (f=0x56232bb13b00, opaque=0x56232b555a60, size=0, field=0x5623289ab6c8 <__compound_literal.3+104>, vmdesc=0x56232ab59fe0) at ../hw/display/virtio-gpu.c:1225

Related to:
https://bugzilla.redhat.com/show_bug.cgi?id=2236353

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>

hw/display/virtio-gpu.c

@@ -26,6 +26,7 @@
 #include "hw/virtio/virtio-gpu-pixman.h"
 #include "hw/virtio/virtio-bus.h"
 #include "hw/qdev-properties.h"
+#include "migration/blocker.h"
 #include "qemu/log.h"
 #include "qemu/module.h"
 #include "qapi/error.h"
@@ -40,6 +41,8 @@ virtio_gpu_find_check_resource(VirtIOGPU *g, uint32_t resource_id,
 
 static void virtio_gpu_reset_bh(void *opaque);
 
+static Error *blob_mig_blocker;
+
 void virtio_gpu_update_cursor_data(VirtIOGPU *g,
                                    struct virtio_gpu_scanout *s,
                                    uint32_t resource_id)
@@ -1373,6 +1376,14 @@ void virtio_gpu_device_realize(DeviceState *qdev, Error **errp)
             error_setg(errp, "blobs and virgl are not compatible (yet)");
             return;
         }
+
+        if (!blob_mig_blocker) {
+            error_setg(&blob_mig_blocker,
+                       "virtio-gpu blob VMs are currently not migratable.");
+        }
+        if (migrate_add_blocker(blob_mig_blocker, errp)) {
+            return;
+        }
     }
 
     if (!virtio_gpu_base_device_realize(qdev,
@@ -1399,6 +1410,9 @@ static void virtio_gpu_device_unrealize(DeviceState *qdev)
 {
     VirtIOGPU *g = VIRTIO_GPU(qdev);
 
+    if (virtio_gpu_blob_enabled(g->parent_obj.conf)) {
+        migrate_del_blocker(blob_mig_blocker);
+    }
     g_clear_pointer(&g->ctrl_bh, qemu_bh_delete);
     g_clear_pointer(&g->cursor_bh, qemu_bh_delete);
     g_clear_pointer(&g->reset_bh, qemu_bh_delete);