qdict: Make qdict_flatten() shallow-clone-friendly

In its current form, qdict_flatten() removes all entries from nested
QDicts that are moved to the root QDict.  It is completely sufficient to
remove all old entries from the root QDict, however.  If the nested
dicts have a refcount of 1, this will automatically delete them, too.
And if they have a greater refcount, we probably do not want to modify
them in the first place.

The latter observation means that it was currently (in general)
impossible to qdict_flatten() a shallowly cloned dict because that would
empty nested QDicts in the original dict as well.  This patch changes
this, so you can now use qdict_flatten(qdict_shallow_clone(dict)) to get
a flattened copy without disturbing the original.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20180611205203.2624-7-mreitz@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 15 insertions, 4 deletions

diff --git a/qobject/block-qdict.c b/qobject/block-qdict.c
index df833083a7..36129e7379 100644
--- a/qobject/block-qdict.c
+++ b/qobject/block-qdict.c
@@ -114,19 +114,30 @@ static void qdict_flatten_qdict(QDict *qdict, QDict *target, const char *prefix)
 
         /*
          * Flatten non-empty QDict and QList recursively into @target,
-         * copy other objects to @target
+         * copy other objects to @target.
+         * On the root level (if @qdict == @target), remove flattened
+         * nested QDicts and QLists from @qdict.
+         *
+         * (Note that we do not need to remove entries from nested
+         * dicts or lists.  Their reference count is decremented on
+         * the root level, so there are no leaks.  In fact, if they
+         * have a reference count greater than one, we are probably
+         * well advised not to modify them altogether.)
          */
         if (dict_val && qdict_size(dict_val)) {
             qdict_flatten_qdict(dict_val, target,
                                 new_key ? new_key : entry->key);
-            qdict_del(qdict, entry->key);
+            if (target == qdict) {
+                qdict_del(qdict, entry->key);
+            }
         } else if (list_val && !qlist_empty(list_val)) {
             qdict_flatten_qlist(list_val, target,
                                 new_key ? new_key : entry->key);
-            qdict_del(qdict, entry->key);
+            if (target == qdict) {
+                qdict_del(qdict, entry->key);
+            }
         } else if (target != qdict) {
             qdict_put_obj(target, new_key, qobject_ref(value));
-            qdict_del(qdict, entry->key);
         }
 
         g_free(new_key);