qom: Add can_be_deleted callback to UserCreatableClass

If backends implement the can_be_deleted and it returns false,
Then the qmp_object_del won't delete the given backends.

Signed-off-by: Lin Ma <lma@suse.com>
Message-Id: <1427704589-7688-2-git-send-email-lma@suse.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qom/object_interfaces.h

@@ -25,6 +25,8 @@ typedef struct UserCreatable {
  * UserCreatableClass:
  * @parent_class: the base class
  * @complete: callback to be called after @obj's properties are set.
+ * @can_be_deleted: callback to be called before an object is removed
+ * to check if @obj can be removed safely.
  *
  * Interface is designed to work with -object/object-add/object_add
  * commands.
@@ -47,6 +49,7 @@ typedef struct UserCreatableClass {
 
     /* <public> */
     void (*complete)(UserCreatable *uc, Error **errp);
+    bool (*can_be_deleted)(UserCreatable *uc, Error **errp);
 } UserCreatableClass;
 
 /**
@@ -59,4 +62,14 @@ typedef struct UserCreatableClass {
  * nothing.
  */
 void user_creatable_complete(Object *obj, Error **errp);
+
+/**
+ * user_creatable_can_be_deleted:
+ * @uc: the object whose can_be_deleted() method is called if implemented
+ * @errp: if an error occurs, a pointer to an area to store the error
+ *
+ * Wrapper to call can_be_deleted() method if one of types it's inherited
+ * from implements USER_CREATABLE interface.
+ */
+bool user_creatable_can_be_deleted(UserCreatable *uc, Error **errp);
 #endif

qmp.c

@@ -711,6 +711,11 @@ void qmp_object_del(const char *id, Error **errp)
         error_setg(errp, "object id not found");
         return;
     }
+
+    if (!user_creatable_can_be_deleted(USER_CREATABLE(obj), errp)) {
+        error_setg(errp, "%s is in use, can not be deleted", id);
+        return;
+    }
     object_unparent(obj);
 }
 

qom/object_interfaces.c

@@ -18,6 +18,18 @@ void user_creatable_complete(Object *obj, Error **errp)
     }
 }
 
+bool user_creatable_can_be_deleted(UserCreatable *uc, Error **errp)
+{
+
+    UserCreatableClass *ucc = USER_CREATABLE_GET_CLASS(uc);
+
+    if (ucc->can_be_deleted) {
+        return ucc->can_be_deleted(uc, errp);
+    } else {
+        return true;
+    }
+}
+
 static void register_types(void)
 {
     static const TypeInfo uc_interface_info = {