Use vmstate_save_state_with_err() to improve error reporting in the
callers and store a reported error under the migration stream. Add
documentation while at it.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 include/hw/vfio/vfio-common.h | 25 ++++++++++++++++++++++++-
 hw/vfio/migration.c           | 18 ++++++++++++------
 hw/vfio/pci.c                 |  5 +++--
 3 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index b9da6c08ef41174610eb92726c590309a53696a3..46f88493634b5634a9c14a5caa33a463fbf2c50d 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -133,7 +133,30 @@ struct VFIODeviceOps {
     int (*vfio_hot_reset_multi)(VFIODevice *vdev);
     void (*vfio_eoi)(VFIODevice *vdev);
     Object *(*vfio_get_object)(VFIODevice *vdev);
-    void (*vfio_save_config)(VFIODevice *vdev, QEMUFile *f);
+
+    /**
+     * @vfio_save_config
+     *
+     * Save device config state
+     *
+     * @vdev: #VFIODevice for which to save the config
+     * @f: #QEMUFile where to send the data
+     * @errp: pointer to Error*, to store an error if it happens.
+     *
+     * Returns zero to indicate success and negative for error
+     */
+    int (*vfio_save_config)(VFIODevice *vdev, QEMUFile *f, Error **errp);
+
+    /**
+     * @vfio_load_config
+     *
+     * Load device config state
+     *
+     * @vdev: #VFIODevice for which to load the config
+     * @f: #QEMUFile where to get the data
+     *
+     * Returns zero to indicate success and negative for error
+     */
     int (*vfio_load_config)(VFIODevice *vdev, QEMUFile *f);
 };
 
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index a67c3e457aa8255e7e39db5127627524d75a55dd..4c4ccbaed10b82e7baa992770ec0ec5a6c82b757 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -190,14 +190,19 @@ static int vfio_load_buffer(QEMUFile *f, VFIODevice *vbasedev,
     return ret;
 }
 
-static int vfio_save_device_config_state(QEMUFile *f, void *opaque)
+static int vfio_save_device_config_state(QEMUFile *f, void *opaque,
+                                         Error **errp)
 {
     VFIODevice *vbasedev = opaque;
+    int ret;
 
     qemu_put_be64(f, VFIO_MIG_FLAG_DEV_CONFIG_STATE);
 
     if (vbasedev->ops && vbasedev->ops->vfio_save_config) {
-        vbasedev->ops->vfio_save_config(vbasedev, f);
+        ret = vbasedev->ops->vfio_save_config(vbasedev, f, errp);
+        if (ret) {
+            return ret;
+        }
     }
 
     qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
@@ -587,13 +592,14 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
 static void vfio_save_state(QEMUFile *f, void *opaque)
 {
     VFIODevice *vbasedev = opaque;
+    Error *local_err = NULL;
     int ret;
 
-    ret = vfio_save_device_config_state(f, opaque);
+    ret = vfio_save_device_config_state(f, opaque, &local_err);
     if (ret) {
-        error_report("%s: Failed to save device config space",
-                     vbasedev->name);
-        qemu_file_set_error(f, ret);
+        error_prepend(&local_err, "%s: Failed to save device config space",
+                      vbasedev->name);
+        qemu_file_set_error_obj(f, ret, local_err);
     }
 }
 
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 4fa387f0430d62ca2ba1b5ae5b7037f8f06b33f9..99d86e1d40ef25133fc76ad6e58294b07bd20843 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2585,11 +2585,12 @@ const VMStateDescription vmstate_vfio_pci_config = {
     }
 };
 
-static void vfio_pci_save_config(VFIODevice *vbasedev, QEMUFile *f)
+static int vfio_pci_save_config(VFIODevice *vbasedev, QEMUFile *f, Error **errp)
 {
     VFIOPCIDevice *vdev = container_of(vbasedev, VFIOPCIDevice, vbasedev);
 
-    vmstate_save_state(f, &vmstate_vfio_pci_config, vdev, NULL);
+    return vmstate_save_state_with_err(f, &vmstate_vfio_pci_config, vdev, NULL,
+                                       errp);
 }
 
 static int vfio_pci_load_config(VFIODevice *vbasedev, QEMUFile *f)
-- 
2.44.0