qapi: Simplify excess input reporting in input visitors

When reporting that an unvisited member remains at the end of an
input visit for a struct, we were using g_hash_table_find()
coupled with a callback function that always returns true, to
locate an arbitrary member of the hash table.  But if all we
need is an arbitrary entry, we can get that from a single-use
iterator, without needing a tautological callback function.

Technically, our cast of &(GQueue *) to (void **) is not strict
C (while void * must be able to hold all other pointers, nothing
says a void ** has to be the same width or representation as a
GQueue **).  The kosher way to write it would be the verbose:

    void *tmp;
    GQueue *any;
    if (g_hash_table_iter_next(&iter, NULL, &tmp)) {
        any = tmp;

But our code base (not to mention glib itself) already has other
cases of assuming that ALL pointers have the same width and
representation, where a compiler would have to go out of its way
to mis-compile our borderline behavior.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1455778109-6278-2-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 5 insertions, 9 deletions

diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 362a1a3..2f48b95 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -90,12 +90,6 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp)
     qiv->nb_stack++;
 }
 
-/** Only for qmp_input_pop. */
-static gboolean always_true(gpointer key, gpointer val, gpointer user_pkey)
-{
-    *(const char **)user_pkey = (const char *)key;
-    return TRUE;
-}
 
 static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
 {
@@ -104,9 +98,11 @@ static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
     if (qiv->strict) {
         GHashTable * const top_ht = qiv->stack[qiv->nb_stack - 1].h;
         if (top_ht) {
-            if (g_hash_table_size(top_ht)) {
-                const char *key;
-                g_hash_table_find(top_ht, always_true, &key);
+            GHashTableIter iter;
+            const char *key;
+
+            g_hash_table_iter_init(&iter, top_ht);
+            if (g_hash_table_iter_next(&iter, (void **)&key, NULL)) {
                 error_setg(errp, QERR_QMP_EXTRA_MEMBER, key);
             }
             g_hash_table_unref(top_ht);