block: Fix -blockdev / blockdev-add for empty objects and arrays

-blockdev and blockdev-add silently ignore empty objects and arrays in
their argument.  That's because qmp_blockdev_add() converts the
argument to a flat QDict, and qdict_flatten() eats empty QDict and
QList members.  For instance, we ignore an empty BlockdevOptions
member @cache.  No real harm, as absent means the same as empty there.

Thus, the flaw puts an artificial restriction on the QAPI schema: we
can't have potentially empty objects and arrays within
BlockdevOptions, except when they're optional and "empty" has the same
meaning as "absent".

Our QAPI schema satisfies this restriction (I checked), but it's a
trap for the unwary, and a temptation to employ awkward workarounds
for the wary.  Let's get rid of it.

Change qdict_flatten() and qdict_crumple() to treat empty dictionaries
and lists exactly like scalars.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 63 insertions, 29 deletions

diff --git a/qobject/block-qdict.c b/qobject/block-qdict.c
index e51a3d2c0f..df833083a7 100644
--- a/qobject/block-qdict.c
+++ b/qobject/block-qdict.c
@@ -56,6 +56,8 @@ static void qdict_flatten_qlist(QList *qlist, QDict *target, const char *prefix)
 {
     QObject *value;
     const QListEntry *entry;
+    QDict *dict_val;
+    QList *list_val;
     char *new_key;
     int i;
 
@@ -69,16 +71,18 @@ static void qdict_flatten_qlist(QList *qlist, QDict *target, const char *prefix)
 
     for (i = 0; entry; entry = qlist_next(entry), i++) {
         value = qlist_entry_obj(entry);
+        dict_val = qobject_to(QDict, value);
+        list_val = qobject_to(QList, value);
         new_key = g_strdup_printf("%s.%i", prefix, i);
 
         /*
          * Flatten non-empty QDict and QList recursively into @target,
          * copy other objects to @target
          */
-        if (qobject_type(value) == QTYPE_QDICT) {
-            qdict_flatten_qdict(qobject_to(QDict, value), target, new_key);
-        } else if (qobject_type(value) == QTYPE_QLIST) {
-            qdict_flatten_qlist(qobject_to(QList, value), target, new_key);
+        if (dict_val && qdict_size(dict_val)) {
+            qdict_flatten_qdict(dict_val, target, new_key);
+        } else if (list_val && !qlist_empty(list_val)) {
+            qdict_flatten_qlist(list_val, target, new_key);
         } else {
             qdict_put_obj(target, new_key, qobject_ref(value));
         }
@@ -91,6 +95,8 @@ static void qdict_flatten_qdict(QDict *qdict, QDict *target, const char *prefix)
 {
     QObject *value;
     const QDictEntry *entry, *next;
+    QDict *dict_val;
+    QList *list_val;
     char *new_key;
 
     entry = qdict_first(qdict);
@@ -98,6 +104,8 @@ static void qdict_flatten_qdict(QDict *qdict, QDict *target, const char *prefix)
     while (entry != NULL) {
         next = qdict_next(qdict, entry);
         value = qdict_entry_value(entry);
+        dict_val = qobject_to(QDict, value);
+        list_val = qobject_to(QList, value);
         new_key = NULL;
 
         if (prefix) {
@@ -108,12 +116,12 @@ 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
          */
-        if (qobject_type(value) == QTYPE_QDICT) {
-            qdict_flatten_qdict(qobject_to(QDict, value), target,
+        if (dict_val && qdict_size(dict_val)) {
+            qdict_flatten_qdict(dict_val, target,
                                 new_key ? new_key : entry->key);
             qdict_del(qdict, entry->key);
-        } else if (qobject_type(value) == QTYPE_QLIST) {
-            qdict_flatten_qlist(qobject_to(QList, value), target,
+        } 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);
         } else if (target != qdict) {
@@ -127,10 +135,11 @@ static void qdict_flatten_qdict(QDict *qdict, QDict *target, const char *prefix)
 }
 
 /**
- * qdict_flatten(): For each nested QDict with key x, all fields with key y
- * are moved to this QDict and their key is renamed to "x.y". For each nested
- * QList with key x, the field at index y is moved to this QDict with the key
- * "x.y" (i.e., the reverse of what qdict_array_split() does).
+ * qdict_flatten(): For each nested non-empty QDict with key x, all
+ * fields with key y are moved to this QDict and their key is renamed
+ * to "x.y". For each nested non-empty QList with key x, the field at
+ * index y is moved to this QDict with the key "x.y" (i.e., the
+ * reverse of what qdict_array_split() does).
  * This operation is applied recursively for nested QDicts and QLists.
  */
 void qdict_flatten(QDict *qdict)
@@ -361,8 +370,8 @@ static int qdict_is_list(QDict *maybe_list, Error **errp)
  * @src: the original flat dictionary (only scalar values) to crumple
  *
  * Takes a flat dictionary whose keys use '.' separator to indicate
- * nesting, and values are scalars, and crumples it into a nested
- * structure.
+ * nesting, and values are scalars, empty dictionaries or empty lists,
+ * and crumples it into a nested structure.
  *
  * To include a literal '.' in a key name, it must be escaped as '..'
  *
@@ -399,6 +408,8 @@ QObject *qdict_crumple(const QDict *src, Error **errp)
 {
     const QDictEntry *ent;
     QDict *two_level, *multi_level = NULL, *child_dict;
+    QDict *dict_val;
+    QList *list_val;
     QObject *dst = NULL, *child;
     size_t i;
     char *prefix = NULL;
@@ -409,10 +420,11 @@ QObject *qdict_crumple(const QDict *src, Error **errp)
 
     /* Step 1: split our totally flat dict into a two level dict */
     for (ent = qdict_first(src); ent != NULL; ent = qdict_next(src, ent)) {
-        if (qobject_type(ent->value) == QTYPE_QDICT ||
-            qobject_type(ent->value) == QTYPE_QLIST) {
-            error_setg(errp, "Value %s is not a scalar",
-                       ent->key);
+        dict_val = qobject_to(QDict, ent->value);
+        list_val = qobject_to(QList, ent->value);
+        if ((dict_val && qdict_size(dict_val))
+            || (list_val && !qlist_empty(list_val))) {
+            error_setg(errp, "Value %s is not flat", ent->key);
             goto error;
         }
 
@@ -451,9 +463,9 @@ QObject *qdict_crumple(const QDict *src, Error **errp)
     multi_level = qdict_new();
     for (ent = qdict_first(two_level); ent != NULL;
          ent = qdict_next(two_level, ent)) {
-        QDict *dict = qobject_to(QDict, ent->value);
-        if (dict) {
-            child = qdict_crumple(dict, errp);
+        dict_val = qobject_to(QDict, ent->value);
+        if (dict_val && qdict_size(dict_val)) {
+            child = qdict_crumple(dict_val, errp);
             if (!child) {
                 goto error;
             }
diff --git a/tests/check-block-qdict.c b/tests/check-block-qdict.c
index 2da16f01a6..1d20fccbd4 100644
--- a/tests/check-block-qdict.c
+++ b/tests/check-block-qdict.c
@@ -79,10 +79,10 @@ static void qdict_flatten_test(void)
      *     "e.1.2.b": 1,
      *     "f.c": 2,
      *     "f.d": 3,
-     *     "g": 4
+     *     "g": 4,
+     *     "y.0": {},
+     *     "z.a": []
      * }
-     *
-     * Note that "y" and "z" get eaten.
      */
 
     qdict_put_int(e_1_2, "a", 0);
@@ -117,8 +117,10 @@ static void qdict_flatten_test(void)
     g_assert(qdict_get_int(root, "f.c") == 2);
     g_assert(qdict_get_int(root, "f.d") == 3);
     g_assert(qdict_get_int(root, "g") == 4);
+    g_assert(!qdict_size(qdict_get_qdict(root, "y.0")));
+    g_assert(qlist_empty(qdict_get_qlist(root, "z.a")));
 
-    g_assert(qdict_size(root) == 8);
+    g_assert(qdict_size(root) == 10);
 
     qobject_unref(root);
 }
@@ -387,7 +389,8 @@ static void qdict_join_test(void)
 static void qdict_crumple_test_recursive(void)
 {
     QDict *src, *dst, *rule, *vnc, *acl, *listen;
-    QList *rules;
+    QDict *empty, *empty_dict, *empty_list_0;
+    QList *rules, *empty_list, *empty_dict_a;
 
     src = qdict_new();
     qdict_put_str(src, "vnc.listen.addr", "127.0.0.1");
@@ -399,10 +402,12 @@ static void qdict_crumple_test_recursive(void)
     qdict_put_str(src, "vnc.acl.default", "deny");
     qdict_put_str(src, "vnc.acl..name", "acl0");
     qdict_put_str(src, "vnc.acl.rule..name", "acl0");
+    qdict_put(src, "empty.dict.a", qlist_new());
+    qdict_put(src, "empty.list.0", qdict_new());
 
     dst = qobject_to(QDict, qdict_crumple(src, &error_abort));
     g_assert(dst);
-    g_assert_cmpint(qdict_size(dst), ==, 1);
+    g_assert_cmpint(qdict_size(dst), ==, 2);
 
     vnc = qdict_get_qdict(dst, "vnc");
     g_assert(vnc);
@@ -440,6 +445,21 @@ static void qdict_crumple_test_recursive(void)
     g_assert_cmpstr("acl0", ==, qdict_get_str(vnc, "acl.name"));
     g_assert_cmpstr("acl0", ==, qdict_get_str(acl, "rule.name"));
 
+    empty = qdict_get_qdict(dst, "empty");
+    g_assert(empty);
+    g_assert_cmpint(qdict_size(empty), ==, 2);
+    empty_dict = qdict_get_qdict(empty, "dict");
+    g_assert(empty_dict);
+    g_assert_cmpint(qdict_size(empty_dict), ==, 1);
+    empty_dict_a = qdict_get_qlist(empty_dict, "a");
+    g_assert(empty_dict_a && qlist_empty(empty_dict_a));
+    empty_list = qdict_get_qlist(empty, "list");
+    g_assert(empty_list);
+    g_assert_cmpint(qlist_size(empty_list), ==, 1);
+    empty_list_0 = qobject_to(QDict, qlist_pop(empty_list));
+    g_assert(empty_list_0);
+    g_assert_cmpint(qdict_size(empty_list_0), ==, 0);
+
     qobject_unref(src);
     qobject_unref(dst);
 }
@@ -587,7 +607,7 @@ static void qdict_rename_keys_test(void)
 
 static void qdict_crumple_test_bad_inputs(void)
 {
-    QDict *src;
+    QDict *src, *nested;
     Error *error = NULL;
 
     src = qdict_new();
@@ -614,7 +634,9 @@ static void qdict_crumple_test_bad_inputs(void)
 
     src = qdict_new();
     /* The input should be flat, ie no dicts or lists */
-    qdict_put(src, "rule.a", qdict_new());
+    nested = qdict_new();
+    qdict_put(nested, "x", qdict_new());
+    qdict_put(src, "rule.a", nested);
     qdict_put_str(src, "rule.b", "allow");
 
     g_assert(qdict_crumple(src, &error) == NULL);