This will be useful to report errors at a higher level, mostly in VFIO
today.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---

 Changes in v3:

 - ERRP_GUARD() because of error_prepend use 
 - Made sure an error is always set in case of failure in
   vfio_load_setup()

 include/migration/register.h |  3 ++-
 hw/vfio/migration.c          |  9 +++++++--
 migration/ram.c              |  3 ++-
 migration/savevm.c           | 11 +++++++----
 4 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/include/migration/register.h b/include/migration/register.h
index 64fc7c11036c82edd6d69513e56a0216d36c17aa..f60e797894e5faacdf55d2d6de175074ac58944f 100644
--- a/include/migration/register.h
+++ b/include/migration/register.h
@@ -234,10 +234,11 @@ typedef struct SaveVMHandlers {
      *
      * @f: QEMUFile where to receive the data
      * @opaque: data pointer passed to register_savevm_live()
+     * @errp: pointer to Error*, to store an error if it happens.
      *
      * Returns zero to indicate success and negative for error
      */
-    int (*load_setup)(QEMUFile *f, void *opaque);
+    int (*load_setup)(QEMUFile *f, void *opaque, Error **errp);
 
     /**
      * @load_cleanup
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 3e893093ea6191fda35b7fdaddad5bff23e97a13..a3bb1a92ba0b9c2c585efe54cfda0b774a81dcb9 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -588,12 +588,17 @@ static void vfio_save_state(QEMUFile *f, void *opaque)
     }
 }
 
-static int vfio_load_setup(QEMUFile *f, void *opaque)
+static int vfio_load_setup(QEMUFile *f, void *opaque, Error **errp)
 {
     VFIODevice *vbasedev = opaque;
+    int ret;
 
-    return vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_RESUMING,
+    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_RESUMING,
                                    vbasedev->migration->device_state);
+    if (ret) {
+        error_setg(errp, "%s: Failed to set RESUMING state", vbasedev->name);
+    }
+    return ret;
 }
 
 static int vfio_load_cleanup(void *opaque)
diff --git a/migration/ram.c b/migration/ram.c
index 52ad519b305532284003d78b93dd4a7186c767af..c5149b7d717aefad7f590422af0ea4a40e7507be 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3678,8 +3678,9 @@ void colo_release_ram_cache(void)
  *
  * @f: QEMUFile where to receive the data
  * @opaque: RAMState pointer
+ * @errp: pointer to Error*, to store an error if it happens.
  */
-static int ram_load_setup(QEMUFile *f, void *opaque)
+static int ram_load_setup(QEMUFile *f, void *opaque, Error **errp)
 {
     xbzrle_load_setup();
     ramblock_recv_map_init();
diff --git a/migration/savevm.c b/migration/savevm.c
index 52d35b2a72c6238bfe5dcb4d81c1af8d2bf73013..ed0d1f31bee9b671698a75c29ab448ee2812685d 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2750,8 +2750,9 @@ static void qemu_loadvm_state_switchover_ack_needed(MigrationIncomingState *mis)
     trace_loadvm_state_switchover_ack_needed(mis->switchover_ack_pending_num);
 }
 
-static int qemu_loadvm_state_setup(QEMUFile *f)
+static int qemu_loadvm_state_setup(QEMUFile *f, Error **errp)
 {
+    ERRP_GUARD(); /* error_prepend use */
     SaveStateEntry *se;
     int ret;
 
@@ -2766,10 +2767,11 @@ static int qemu_loadvm_state_setup(QEMUFile *f)
             }
         }
 
-        ret = se->ops->load_setup(f, se->opaque);
+        ret = se->ops->load_setup(f, se->opaque, errp);
         if (ret < 0) {
+            error_prepend(errp, "Load state of device %s failed: ",
+                          se->idstr);
             qemu_file_set_error(f, ret);
-            error_report("Load state of device %s failed", se->idstr);
             return ret;
         }
     }
@@ -2950,7 +2952,8 @@ int qemu_loadvm_state(QEMUFile *f)
         return ret;
     }
 
-    if (qemu_loadvm_state_setup(f) != 0) {
+    if (qemu_loadvm_state_setup(f, &local_err) != 0) {
+        error_report_err(local_err);
         return -EINVAL;
     }
 
-- 
2.44.0