migration: wire vmstate_save_state errors up to vmstate_subsection_save

Route the errors from vmstate_save_state up through
vmstate_subsection_save (and back down, all rather recursive).

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170925112917.21340-5-dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  Commit message fixed up as per Peter's review

migration/vmstate.c

@@ -21,8 +21,8 @@
 #include "trace.h"
 #include "qjson.h"
 
-static void vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
-                                    void *opaque, QJSON *vmdesc);
+static int vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
+                                   void *opaque, QJSON *vmdesc);
 static int vmstate_subsection_load(QEMUFile *f, const VMStateDescription *vmsd,
                                    void *opaque);
 
@@ -395,9 +395,7 @@ int vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
         json_end_array(vmdesc);
     }
 
-    vmstate_subsection_save(f, vmsd, opaque, vmdesc);
-
-    return 0;
+    return vmstate_subsection_save(f, vmsd, opaque, vmdesc);
 }
 
 static const VMStateDescription *
@@ -463,11 +461,12 @@ static int vmstate_subsection_load(QEMUFile *f, const VMStateDescription *vmsd,
     return 0;
 }
 
-static void vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
-                                    void *opaque, QJSON *vmdesc)
+static int vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
+                                   void *opaque, QJSON *vmdesc)
 {
     const VMStateDescription **sub = vmsd->subsections;
     bool subsection_found = false;
+    int ret = 0;
 
     trace_vmstate_subsection_save_top(vmsd->name);
     while (sub && *sub && (*sub)->needed) {
@@ -491,7 +490,10 @@ static void vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
             qemu_put_byte(f, len);
             qemu_put_buffer(f, (uint8_t *)vmsdsub->name, len);
             qemu_put_be32(f, vmsdsub->version_id);
-            vmstate_save_state(f, vmsdsub, opaque, vmdesc);
+            ret = vmstate_save_state(f, vmsdsub, opaque, vmdesc);
+            if (ret) {
+                return ret;
+            }
 
             if (vmdesc) {
                 json_end_object(vmdesc);
@@ -503,4 +505,6 @@ static void vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
     if (vmdesc && subsection_found) {
         json_end_array(vmdesc);
     }
+
+    return ret;
 }