[Qemu-devel] [PATCH v13 04/18] qmp-input: Clean up stack handling

[Eric Blake]

Management of the top of stack was a bit verbose; creating a
temporary variable and adding some comments makes the existing
code more legible before the next few patches improve things.
No semantic changes other than asserting that we are always
visiting a QObject, and not a NULL value.

Signed-off-by: Eric Blake <ebl...@redhat.com>

---
v13: no change
v12: new patch
---
 qapi/qmp-input-visitor.c | 52 ++++++++++++++++++++++++++++++++++--------------
 1 file changed, 37 insertions(+), 15 deletions(-)

diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 550aed6..7428d15 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -24,16 +24,26 @@

 typedef struct StackObject
 {
-    QObject *obj;
+    QObject *obj; /* Object being visited */
+
+    /* If obj is list: NULL if list is at head, otherwise tail of list
+     * still needing visits */
     const QListEntry *entry;
-    GHashTable *h;
+
+    GHashTable *h; /* If obj is dict: remaining keys needing visits */
 } StackObject;

 struct QmpInputVisitor
 {
     Visitor visitor;
+
+    /* Stack of objects being visited.  stack[0] is root of visit,
+     * stack[1] and below correspond to visit_start_struct (nested
+     * QDict) and visit_start_list (nested QList).  */
     StackObject stack[QIV_STACK_SIZE];
     int nb_stack;
+
+    /* True to track whether all keys in QDict have been parsed.  */
     bool strict;
 };

@@ -46,19 +56,29 @@ static QObject *qmp_input_get_object(QmpInputVisitor *qiv,
                                      const char *name,
                                      bool consume)
 {
-    QObject *qobj = qiv->stack[qiv->nb_stack - 1].obj;
+    StackObject *tos = &qiv->stack[qiv->nb_stack - 1];
+    QObject *qobj = tos->obj;

-    if (qobj) {
-        if (name && qobject_type(qobj) == QTYPE_QDICT) {
-            if (qiv->stack[qiv->nb_stack - 1].h && consume) {
-                g_hash_table_remove(qiv->stack[qiv->nb_stack - 1].h, name);
-            }
-            return qdict_get(qobject_to_qdict(qobj), name);
-        } else if (qiv->stack[qiv->nb_stack - 1].entry) {
-            return qlist_entry_obj(qiv->stack[qiv->nb_stack - 1].entry);
+    assert(qobj);
+
+    /* If we have a name, and we're in a dictionary, then return that
+     * value. */
+    if (name && qobject_type(qobj) == QTYPE_QDICT) {
+        if (tos->h && consume) {
+            g_hash_table_remove(tos->h, name);
         }
+        return qdict_get(qobject_to_qdict(qobj), name);
     }

+    /* If we are in the middle of a list, then return the next element
+     * of the list.  */
+    if (tos->entry) {
+        assert(qobject_type(qobj) == QTYPE_QLIST);
+        return qlist_entry_obj(tos->entry);
+    }
+
+    /* Otherwise, we are at the root of the visit or the start of a
+     * list, and return the object as-is.  */
     return qobj;
 }

@@ -71,20 +91,22 @@ static void qdict_add_key(const char *key, QObject *obj, 
void *opaque)
 static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp)
 {
     GHashTable *h;
+    StackObject *tos = &qiv->stack[qiv->nb_stack];

+    assert(obj);
     if (qiv->nb_stack >= QIV_STACK_SIZE) {
         error_setg(errp, "An internal buffer overran");
         return;
     }

-    qiv->stack[qiv->nb_stack].obj = obj;
-    qiv->stack[qiv->nb_stack].entry = NULL;
-    qiv->stack[qiv->nb_stack].h = NULL;
+    tos->obj = obj;
+    tos->entry = NULL;
+    tos->h = NULL;

     if (qiv->strict && qobject_type(obj) == QTYPE_QDICT) {
         h = g_hash_table_new(g_str_hash, g_str_equal);
         qdict_iter(qobject_to_qdict(obj), qdict_add_key, h);
-        qiv->stack[qiv->nb_stack].h = h;
+        tos->h = h;
     }

     qiv->nb_stack++;
-- 
2.5.0