migration: add comment for TYPE_MIGRATE

It'll be strange that the migration object inherits TYPE_DEVICE. Add
some explanations to it.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <1498634144-26508-1-git-send-email-peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

diff --git a/migration/migration.c b/migration/migration.c
index b1b0825..2398a9d 100644 (file)
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2046,6 +2046,14 @@ static void migration_instance_init(Object *obj)
 
 static const TypeInfo migration_type = {
     .name = TYPE_MIGRATION,
+    /*
+     * NOTE: "migration" itself is not really a device. We used
+     * TYPE_DEVICE here only to leverage some existing QDev features
+     * like "-global" properties, and HW_COMPAT_* fields (which are
+     * finally applied as global properties as well). If one day the
+     * global property feature can be migrated from QDev to QObject in
+     * general, then we can switch to QObject as well.
+     */
     .parent = TYPE_DEVICE,
     .class_init = migration_class_init,
     .class_size = sizeof(MigrationClass),