[PATCH 02/18] migration/vmstate: Introduce vmstate_no_state_to_migrate

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

Introduce a special state to indicate when an object doesn't
have anything in its state to migrate.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 include/migration/vmstate.h | 1 +
 migration/vmstate.c         | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index af7d80cd4e..0922bc8efa 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -195,6 +195,7 @@ struct VMStateDescription {
 };
 
 extern const VMStateDescription vmstate_dummy; /* Exclusively for linux-user */
+extern const VMStateDescription vmstate_no_state_to_migrate;
 
 extern const VMStateInfo vmstate_info_bool;
 
diff --git a/migration/vmstate.c b/migration/vmstate.c
index bafa890384..d640cafad3 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -20,6 +20,13 @@
 #include "trace.h"
 #include "qjson.h"
 
+const VMStateDescription vmstate_no_state_to_migrate = {
+    .name = "empty-state",
+    .fields = (VMStateField[]) {
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static int vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
                                    void *opaque, QJSON *vmdesc);
 static int vmstate_subsection_load(QEMUFile *f, const VMStateDescription *vmsd,
-- 
2.21.3