[Qemu-devel] [PATCH v14 13/19] qmp: Tighten output visitor rules

[Eric Blake]

Add a new qmp_output_visitor_reset(), which must be called before
reusing an exising QmpOutputVisitor on a new root object.  Tighten
assertions to require that qmp_output_get_qobject() can only be
called after pairing a visit_end_* for every visit_start_* (rather
than allowing it to return a partially built object), and that it
must not be called unless at least one visit_type_* or visit_start/
visit_end pair has occurred since creation/reset (the accidental
return of NULL fixed by commit ab8bf1d7 would have been much
easier to diagnose).

Also, check that we are encountering the expected object or list
type (both during visit_end*, and also by validating whether 'name'
was NULL - although the latter may need to change later if we
improve error messages by always passing in a sensible name).
This provides protection against mismatched push(struct)/pop(list)
or push(list)/pop(struct), similar to the qmp-input protection
added in commit bdd8e6b5.

Signed-off-by: Eric Blake <address@hidden>

---
v14: no change
v13: no change
v12: rebase to latest, move type_null() into earlier patches,
don't change signature of pop, don't auto-reset after a single
get_qobject
[no v10, v11]
v9: rebase to added patch, squash in more sanity checks, drop
Marc-Andre's R-b
v8: rename qmp_output_reset to qmp_output_visitor_reset
v7: new patch, based on discussion about spapr_drc.c
---
 include/qapi/qmp-output-visitor.h |  1 +
 qapi/qmp-output-visitor.c         | 39 +++++++++++++++++++++++----------------
 tests/test-qmp-output-visitor.c   |  6 ++++++
 3 files changed, 30 insertions(+), 16 deletions(-)

diff --git a/include/qapi/qmp-output-visitor.h 
b/include/qapi/qmp-output-visitor.h
index 2266770..5093f0d 100644
--- a/include/qapi/qmp-output-visitor.h
+++ b/include/qapi/qmp-output-visitor.h
@@ -21,6 +21,7 @@ typedef struct QmpOutputVisitor QmpOutputVisitor;

 QmpOutputVisitor *qmp_output_visitor_new(void);
 void qmp_output_visitor_cleanup(QmpOutputVisitor *v);
+void qmp_output_visitor_reset(QmpOutputVisitor *v);

 QObject *qmp_output_get_qobject(QmpOutputVisitor *v);
 Visitor *qmp_output_get_visitor(QmpOutputVisitor *v);
diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c
index 5681ad3..7c48dfb 100644
--- a/qapi/qmp-output-visitor.c
+++ b/qapi/qmp-output-visitor.c
@@ -82,9 +82,8 @@ static void qmp_output_add_obj(QmpOutputVisitor *qov, const 
char *name,
     QObject *cur = e ? e->value : NULL;

     if (!cur) {
-        /* FIXME we should require the user to reset the visitor, rather
-         * than throwing away the previous root */
-        qobject_decref(qov->root);
+        /* Don't allow reuse of visitor on more than one root */
+        assert(!qov->root);
         qov->root = value;
     } else {
         switch (qobject_type(cur)) {
@@ -93,6 +92,9 @@ static void qmp_output_add_obj(QmpOutputVisitor *qov, const 
char *name,
             qdict_put_obj(qobject_to_qdict(cur), name, value);
             break;
         case QTYPE_QLIST:
+            /* FIXME: assertion needs adjustment if we fix visit-core
+             * to pass "name.0" style name during lists.  */
+            assert(!name);
             qlist_append_obj(qobject_to_qlist(cur), value);
             break;
         default:
@@ -114,7 +116,8 @@ static void qmp_output_start_struct(Visitor *v, const char 
*name, void **obj,
 static void qmp_output_end_struct(Visitor *v, Error **errp)
 {
     QmpOutputVisitor *qov = to_qov(v);
-    qmp_output_pop(qov);
+    QObject *value = qmp_output_pop(qov);
+    assert(qobject_type(value) == QTYPE_QDICT);
 }

 static void qmp_output_start_list(Visitor *v, const char *name, Error **errp)
@@ -145,7 +148,8 @@ static GenericList *qmp_output_next_list(Visitor *v, 
GenericList **listp,
 static void qmp_output_end_list(Visitor *v)
 {
     QmpOutputVisitor *qov = to_qov(v);
-    qmp_output_pop(qov);
+    QObject *value = qmp_output_pop(qov);
+    assert(qobject_type(value) == QTYPE_QLIST);
 }

 static void qmp_output_type_int64(Visitor *v, const char *name, int64_t *obj,
@@ -202,18 +206,15 @@ static void qmp_output_type_null(Visitor *v, const char 
*name, Error **errp)
     qmp_output_add_obj(qov, name, qnull());
 }

-/* Finish building, and return the root object. Will not be NULL. */
+/* Finish building, and return the root object. Will not be NULL.
+ * Caller must use qobject_decref() on the result.  */
 QObject *qmp_output_get_qobject(QmpOutputVisitor *qov)
 {
-    /* FIXME: we should require that a visit occurred, and that it is
-     * complete (no starts without a matching end) */
-    QObject *obj = qov->root;
-    if (obj) {
-        qobject_incref(obj);
-    } else {
-        obj = qnull();
-    }
-    return obj;
+    /* A visit must have occurred, with each start paired with end.  */
+    assert(qov->root && !QTAILQ_FIRST(&qov->stack));
+
+    qobject_incref(qov->root);
+    return qov->root;
 }

 Visitor *qmp_output_get_visitor(QmpOutputVisitor *v)
@@ -221,7 +222,7 @@ Visitor *qmp_output_get_visitor(QmpOutputVisitor *v)
     return &v->visitor;
 }

-void qmp_output_visitor_cleanup(QmpOutputVisitor *v)
+void qmp_output_visitor_reset(QmpOutputVisitor *v)
 {
     QStackEntry *e, *tmp;

@@ -231,6 +232,12 @@ void qmp_output_visitor_cleanup(QmpOutputVisitor *v)
     }

     qobject_decref(v->root);
+    v->root = NULL;
+}
+
+void qmp_output_visitor_cleanup(QmpOutputVisitor *v)
+{
+    qmp_output_visitor_reset(v);
     g_free(v);
 }

diff --git a/tests/test-qmp-output-visitor.c b/tests/test-qmp-output-visitor.c
index e656d99..7be33ba 100644
--- a/tests/test-qmp-output-visitor.c
+++ b/tests/test-qmp-output-visitor.c
@@ -139,6 +139,7 @@ static void test_visitor_out_enum(TestOutputVisitorData 
*data,
         g_assert_cmpstr(qstring_get_str(qobject_to_qstring(obj)), ==,
                         EnumOne_lookup[i]);
         qobject_decref(obj);
+        qmp_output_visitor_reset(data->qov);
     }
 }

@@ -153,6 +154,7 @@ static void 
test_visitor_out_enum_errors(TestOutputVisitorData *data,
         visit_type_EnumOne(data->ov, "unused", &bad_values[i], &err);
         g_assert(err);
         error_free(err);
+        qmp_output_visitor_reset(data->qov);
     }
 }

@@ -262,6 +264,7 @@ static void 
test_visitor_out_struct_errors(TestOutputVisitorData *data,
         visit_type_UserDefOne(data->ov, "unused", &pu, &err);
         g_assert(err);
         error_free(err);
+        qmp_output_visitor_reset(data->qov);
     }
 }

@@ -366,6 +369,7 @@ static void test_visitor_out_any(TestOutputVisitorData 
*data,
     qobject_decref(obj);
     qobject_decref(qobj);

+    qmp_output_visitor_reset(data->qov);
     qdict = qdict_new();
     qdict_put(qdict, "integer", qint_from_int(-42));
     qdict_put(qdict, "boolean", qbool_from_bool(true));
@@ -442,6 +446,7 @@ static void 
test_visitor_out_alternate(TestOutputVisitorData *data,
     qapi_free_UserDefAlternate(tmp);
     qobject_decref(arg);

+    qmp_output_visitor_reset(data->qov);
     tmp = g_new0(UserDefAlternate, 1);
     tmp->type = QTYPE_QSTRING;
     tmp->u.s = g_strdup("hello");
@@ -455,6 +460,7 @@ static void 
test_visitor_out_alternate(TestOutputVisitorData *data,
     qapi_free_UserDefAlternate(tmp);
     qobject_decref(arg);

+    qmp_output_visitor_reset(data->qov);
     tmp = g_new0(UserDefAlternate, 1);
     tmp->type = QTYPE_QDICT;
     tmp->u.udfu.integer = 1;
-- 
2.5.5