migration: check pre_save return in vmstate_save_state

Check the return value of pre_save state and fail vmstate_save_state
if the pre_save failed.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170925112917.21340-3-dgilbert@redhat.com>
Reviewed-by: NPeter Xu <peterx@redhat.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>

include/migration/vmstate.h

@@ -994,8 +994,8 @@ extern const VMStateInfo vmstate_info_qtailq;
 
 int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
                        void *opaque, int version_id);
-void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
-                        void *opaque, QJSON *vmdesc);
+int vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
+                       void *opaque, QJSON *vmdesc);
 
 bool vmstate_save_needed(const VMStateDescription *vmsd, void *opaque);
 

migration/trace-events

@@ -40,6 +40,7 @@ savevm_state_iterate(void) ""
 savevm_state_cleanup(void) ""
 savevm_state_complete_precopy(void) ""
 vmstate_save(const char *idstr, const char *vmsd_name) "%s, %s"
+vmstate_save_state_pre_save_res(const char *name, int res) "%s/%d"
 vmstate_save_state_loop(const char *name, const char *field, int n_elems) "%s/%s[%d]"
 vmstate_save_state_top(const char *idstr) "%s"
 vmstate_subsection_save_loop(const char *name, const char *sub) "%s/%s"

migration/vmstate.c

@@ -308,15 +308,21 @@ bool vmstate_save_needed(const VMStateDescription *vmsd, void *opaque)
 }
 
 
-void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
+int vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
                         void *opaque, QJSON *vmdesc)
 {
+    int ret = 0;
     VMStateField *field = vmsd->fields;
 
     trace_vmstate_save_state_top(vmsd->name);
 
     if (vmsd->pre_save) {
-        vmsd->pre_save(opaque);
+        ret = vmsd->pre_save(opaque);
+        trace_vmstate_save_state_pre_save_res(vmsd->name, ret);
+        if (ret) {
+            error_report("pre-save failed: %s", vmsd->name);
+            return ret;
+        }
     }
 
     if (vmdesc) {
@@ -381,6 +387,8 @@ void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
     }
 
     vmstate_subsection_save(f, vmsd, opaque, vmdesc);
+
+    return 0;
 }
 
 static const VMStateDescription *