Add interface to get store weight from memory

glance_store/multi_backend.py

@@ -331,6 +331,34 @@ def verify_store():
         raise RuntimeError(msg)
 
 
+def get_store_weight(store_identifier):
+    """Determine backing store weightage from identifier.
+
+    Given a store identifier, return the appropriate weight of store
+    from memory.
+    """
+    enabled_backends = CONF.enabled_backends
+    enabled_backends.update(_RESERVED_STORES)
+
+    try:
+        scheme = enabled_backends[store_identifier]
+    except KeyError:
+        msg = _("Store for identifier %s not found") % store_identifier
+        raise exceptions.UnknownScheme(msg)
+
+    try:
+        backend_map = location.SCHEME_TO_CLS_BACKEND_MAP[scheme]
+        scheme_info = backend_map[store_identifier]
+    except KeyError:
+        raise exceptions.UnknownScheme(scheme=scheme)
+
+    store = scheme_info['store']
+    if store:
+        return store.weight
+
+    return 0
+
+
 def get_store_from_store_identifier(store_identifier):
     """Determine backing store from identifier.