[Qemu-devel] [PATCH v15 11/23] qmp-input: Refactor when list is advanced

[Eric Blake <eblake@redhat.com>]

In the QMP input visitor, visiting a list traverses two objects:
the QAPI GenericList of the caller (which gets advanced in
visit_next_list() regardless of this patch), and the QList input
that we are converting to QAPI.  For consistency with QDict
visits, we want to consume elements from the input QList during
the visit_type_FOO() for the list element; that is, we want ALL
the code for consuming an input to live in qmp_input_get_object(),
rather than having it split according to whether we are visiting
a dict or a list.  Making qmp_input_get_object() the common point
of consumption will make it easier for a later patch to refactor
visit_start_list() to cover the GenericList * head of a QAPI list,
and in turn will get rid of the 'first' flag (which lived in
qmp_input_next_list() pre-patch, and is hoisted to StackObject
by this patch).

This patch is therefore shifting the post-condition use of
'entry' from:

        start_list next_list type_ELT ... next_list type_ELT end_list
 entry  NULL       1st elt   1st elt      last elt  last elt gone

where type_ELT() returns (entry ? entry : 1st elt) and next_list() steps
entry

to this usage:

        start_list next_list type_ELT ... next_list type_ELT end_list
 entry  1st elt    1nd elt   2nd elt      last elt  NULL     gone

where type_ELT() steps entry and returns the old entry, and next_list()
leaves entry alone.

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

---
v15: rebase, improve commit message, hoist root handling earlier
so that this patch is more pinpointed
v14: no change
v13: no change
v12: new patch
---
 qapi/qmp-input-visitor.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 6409a83..eb77adc 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -29,6 +29,7 @@ typedef struct StackObject

     GHashTable *h;           /* If obj is dict: unvisited keys */
     const QListEntry *entry; /* If obj is list: unvisited tail */
+    bool first;              /* If obj is list: will next_list() visit head */
 } StackObject;

 struct QmpInputVisitor
@@ -80,7 +81,11 @@ static QObject *qmp_input_get_object(QmpInputVisitor *qiv,
     } else {
         assert(qobject_type(qobj) == QTYPE_QLIST);
         assert(!name);
+        assert(!tos->first);
         ret = qlist_entry_obj(tos->entry);
+        if (consume) {
+            tos->entry = qlist_next(tos->entry);
+        }
     }

     return ret;
@@ -104,13 +109,16 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp)
     }

     tos->obj = obj;
-    tos->entry = NULL;
-    tos->h = NULL;
+    assert(!tos->h);
+    assert(!tos->entry);

     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);
         tos->h = h;
+    } else if (qobject_type(obj) == QTYPE_QLIST) {
+        tos->entry = qlist_first(qobject_to_qlist(obj));
+        tos->first = true;
     }

     qiv->nb_stack++;
@@ -119,10 +127,11 @@ static void qmp_input_push(QmpInputVisitor *qiv, QObject *obj, Error **errp)

 static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
 {
+    StackObject *tos = &qiv->stack[qiv->nb_stack - 1];
     assert(qiv->nb_stack > 0);

     if (qiv->strict) {
-        GHashTable * const top_ht = qiv->stack[qiv->nb_stack - 1].h;
+        GHashTable * const top_ht = tos->h;
         if (top_ht) {
             GHashTableIter iter;
             const char *key;
@@ -133,6 +142,7 @@ static void qmp_input_pop(QmpInputVisitor *qiv, Error **errp)
             }
             g_hash_table_unref(top_ht);
         }
+        tos->h = NULL;
     }

     qiv->nb_stack--;
@@ -192,23 +202,15 @@ static GenericList *qmp_input_next_list(Visitor *v, GenericList **list,
     QmpInputVisitor *qiv = to_qiv(v);
     GenericList *entry;
     StackObject *so = &qiv->stack[qiv->nb_stack - 1];
-    bool first;

-    if (so->entry == NULL) {
-        so->entry = qlist_first(qobject_to_qlist(so->obj));
-        first = true;
-    } else {
-        so->entry = qlist_next(so->entry);
-        first = false;
-    }
-
-    if (so->entry == NULL) {
+    if (!so->entry) {
         return NULL;
     }

     entry = g_malloc0(size);
-    if (first) {
+    if (so->first) {
         *list = entry;
+        so->first = false;
     } else {
         (*list)->next = entry;
     }
-- 
2.5.5