savevm: Ignore minimum_version_id_old if there is no load_state_old

At the moment we require vmstate definitions to set minimum_version_id_old
to the same value as minimum_version_id if they do not provide a
load_state_old handler. Since the load_state_old functionality is
required only for a handful of devices that need to retain migration
compatibility with a pre-vmstate implementation, this means the bulk
of devices have pointless boilerplate. Relax the definition so that
minimum_version_id_old is ignored if there is no load_state_old handler.

Note that under the old scheme we would segfault if the vmstate
specified a minimum_version_id_old that was less than minimum_version_id
but did not provide a load_state_old function, and the incoming state
specified a version number between minimum_version_id_old and
minimum_version_id. Under the new scheme this will just result in
our failing the migration.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/vmstate.c b/vmstate.c
index dbb76665d9..b5882fae67 100644
--- a/vmstate.c
+++ b/vmstate.c
@@ -63,11 +63,12 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
     if (version_id > vmsd->version_id) {
         return -EINVAL;
     }
-    if (version_id < vmsd->minimum_version_id_old) {
-        return -EINVAL;
-    }
     if  (version_id < vmsd->minimum_version_id) {
-        return vmsd->load_state_old(f, opaque, version_id);
+        if (vmsd->load_state_old &&
+            version_id >= vmsd->minimum_version_id_old) {
+            return vmsd->load_state_old(f, opaque, version_id);
+        }
+        return -EINVAL;
     }
     if (vmsd->pre_load) {
         int ret = vmsd->pre_load(opaque);