qapi: Add new visit_free() function

Making each visitor provide its own (awkwardly-named) FOO_cleanup()
is unusual, when we can instead have a polymorphic visit_free()
interface. Over the next few patches, we can use the polymorphic
functions to eliminate the need for a FOO_get_visitor() function
for accessing specific visitor functionality, once everything can
be accessed directly through the Visitor* interfaces.

The dealloc visitor is the first one converted to completely use
the new entry point, since qapi_dealloc_visitor_cleanup() was the
only reason that qapi_dealloc_get_visitor() existed, and only
generated and testsuite code was even using it. With the new
visit_free() entry point in place, we no longer need to expose
the QapiDeallocVisitor subtype through qapi_dealloc_visitor_new(),
and can get by with less generated code, with diffs that look like:

| void qapi_free_ACPIOSTInfo(ACPIOSTInfo *obj)
| {
|- QapiDeallocVisitor *qdv;
| Visitor *v;
|
| if (!obj) {
| return;
| }
|
|- qdv = qapi_dealloc_visitor_new();
|- v = qapi_dealloc_get_visitor(qdv);
|+ v = qapi_dealloc_visitor_new();
| visit_type_ACPIOSTInfo(v, NULL, &obj, NULL);
|- qapi_dealloc_visitor_cleanup(qdv);
|+ visit_free(v);
|}

Backports commit 2c0ef9f411ae6081efa9eca5b3eab2dbeee45a6c from qemu

msvc/unicorn/qapi-types.c

@@ -20,17 +20,15 @@
 
 void qapi_free_DummyForceArrays(DummyForceArrays *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_DummyForceArrays(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 const char *const QType_lookup[] = {
@@ -57,32 +55,28 @@ const char *const QapiErrorClass_lookup[] = {
 
 void qapi_free_X86CPUFeatureWordInfo(X86CPUFeatureWordInfo *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_X86CPUFeatureWordInfo(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_X86CPUFeatureWordInfoList(X86CPUFeatureWordInfoList *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_X86CPUFeatureWordInfoList(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 const char *const X86CPURegister32_lookup[] = {
@@ -99,210 +93,182 @@ const char *const X86CPURegister32_lookup[] = {
 
 void qapi_free_anyList(anyList *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_anyList(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_boolList(boolList *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_boolList(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_int16List(int16List *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_int16List(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_int32List(int32List *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_int32List(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_int64List(int64List *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_int64List(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_int8List(int8List *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_int8List(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_intList(intList *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_intList(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_numberList(numberList *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_numberList(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_sizeList(sizeList *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_sizeList(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_strList(strList *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_strList(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_uint16List(uint16List *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_uint16List(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_uint32List(uint32List *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_uint32List(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_uint64List(uint64List *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_uint64List(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 
 void qapi_free_uint8List(uint8List *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_uint8List(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }

qemu/include/qapi/dealloc-visitor.h

@@ -23,9 +23,6 @@ typedef struct QapiDeallocVisitor QapiDeallocVisitor;
  * qapi_free_FOO() functions, and is the only visitor designed to work
  * correctly in the face of a partially-constructed QAPI tree.
  */
-QapiDeallocVisitor *qapi_dealloc_visitor_new(void);
+Visitor *qapi_dealloc_visitor_new(void);
-void qapi_dealloc_visitor_cleanup(QapiDeallocVisitor *d);
-
-Visitor *qapi_dealloc_get_visitor(QapiDeallocVisitor *v);
 
 #endif

qemu/include/qapi/visitor-impl.h

@@ -105,6 +105,9 @@ struct Visitor
 
     /* Must be set */
     VisitorType type;
+
+    /* Must be set */
+    void (*free)(Visitor *v);
 };
 
 #endif

qemu/include/qapi/visitor.h

@@ -39,6 +39,24 @@
  * implemented by each visitor, and docs/qapi-code-gen.txt for more
  * about the QAPI code generator.
  *
+ * All of the visitors are created via:
+ *
+ * Type *subtype_visitor_new(parameters...);
+ *
+ * where Type is either directly 'Visitor *', or is a subtype that can
+ * be trivially upcast to Visitor * via another function:
+ *
+ * Visitor *subtype_get_visitor(SubtypeVisitor *);
+ *
+ * A visitor should be used for exactly one top-level visit_type_FOO()
+ * or virtual walk, then passed to visit_free() to clean up resources.
+ * It is okay to free the visitor without completing the visit, if
+ * some other error is detected in the meantime.  Output visitors
+ * provide an additional function, for collecting the final results of
+ * a successful visit: string_output_get_string() and
+ * qmp_output_get_qobject(); this collection function should not be
+ * called if any errors were reported during the visit.
+ *
  * All QAPI types have a corresponding function with a signature
  * roughly compatible with this:
  *
@@ -225,6 +243,18 @@ typedef struct GenericAlternate {
     char padding[];
 } GenericAlternate;
 
+/*** Visitor cleanup ***/
+
+/*
+ * Free @v and any resources it has tied up.
+ *
+ * May be called whether or not the visit has been successfully
+ * completed, but should not be called until a top-level
+ * visit_type_FOO() or visit_start_ITEM() has been performed on the
+ * visitor.  Safe if @v is NULL.
+ */
+void visit_free(Visitor *v);
+
 
 /*** Visiting structures ***/
 
@@ -276,7 +306,7 @@ void visit_check_struct(Visitor *v, Error **errp);
  * Must be called after any successful use of visit_start_struct(),
  * even if intermediate processing was skipped due to errors, to allow
  * the backend to release any resources.  Destroying the visitor early
- * behaves as if this was implicitly called.
+ * with visit_free() behaves as if this was implicitly called.
  */
 void visit_end_struct(Visitor *v, void **obj);
 
@@ -341,7 +371,7 @@ GenericList *visit_next_list(Visitor *v, GenericList *tail, size_t size);
  * Must be called after any successful use of visit_start_list(), even
  * if intermediate processing was skipped due to errors, to allow the
  * backend to release any resources.  Destroying the visitor early
- * behaves as if this was implicitly called.
+ * with visit_free() behaves as if this was implicitly called.
  */
 void visit_end_list(Visitor *v, void **list);
 
@@ -374,7 +404,7 @@ void visit_start_alternate(Visitor *v, const char *name,
  * Must be called after any successful use of visit_start_alternate(),
  * even if intermediate processing was skipped due to errors, to allow
  * the backend to release any resources.  Destroying the visitor early
- * behaves as if this was implicitly called.
+ * with visit_free() behaves as if this was implicitly called.
  */
 void visit_end_alternate(Visitor *v, void **obj);
 

qemu/qapi/qapi-dealloc-visitor.c

@@ -104,26 +104,16 @@ static void qapi_dealloc_type_anything(Visitor *v, const char *name,
     }
 }
 
-static void qapi_dealloc_type_size(Visitor *v, const char *name, uint64_t *obj,
-                                   Error **errp)
-{
-}
-
 static void qapi_dealloc_type_null(Visitor *v, const char *name, Error **errp)
 {
 }
 
-Visitor *qapi_dealloc_get_visitor(QapiDeallocVisitor *v)
+static void qapi_dealloc_free(Visitor *v)
 {
-    return &v->visitor;
+    g_free(container_of(v, QapiDeallocVisitor, visitor));
 }
 
-void qapi_dealloc_visitor_cleanup(QapiDeallocVisitor *v)
+Visitor *qapi_dealloc_visitor_new(void)
-{
-    g_free(v);
-}
-
-QapiDeallocVisitor *qapi_dealloc_visitor_new(void)
 {
     QapiDeallocVisitor *v;
 
@@ -144,7 +134,7 @@ QapiDeallocVisitor *qapi_dealloc_visitor_new(void)
     v->visitor.type_number = qapi_dealloc_type_number;
     v->visitor.type_any = qapi_dealloc_type_anything;
     v->visitor.type_null = qapi_dealloc_type_null;
-    v->visitor.type_size = qapi_dealloc_type_size;
+    v->visitor.free = qapi_dealloc_free;
 
-    return v;
+    return &v->visitor;
 }

qemu/qapi/qapi-visit-core.c

@@ -21,6 +21,13 @@
 #include "qapi/visitor.h"
 #include "qapi/visitor-impl.h"
 
+void visit_free(Visitor *v)
+{
+    if (v) {
+        v->free(v);
+    }
+}
+
 void visit_start_struct(Visitor *v, const char *name, void **obj,
                         size_t size, Error **errp)
 {

qemu/qapi/qmp-input-visitor.c

@@ -379,6 +379,13 @@ Visitor *qmp_input_get_visitor(QmpInputVisitor *v)
     return &v->visitor;
 }
 
+static void qmp_input_free(Visitor *v)
+{
+    QmpInputVisitor *qiv = to_qiv(v);
+
+    qmp_input_visitor_cleanup(qiv);
+}
+
 void qmp_input_visitor_cleanup(QmpInputVisitor *v)
 {
     qobject_decref(v->root);
@@ -407,6 +414,7 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj, bool strict)
     v->visitor.type_any = qmp_input_type_any;
     v->visitor.type_null = qmp_input_type_null;
     v->visitor.optional = qmp_input_optional;
+    v->visitor.free = qmp_input_free;
     v->strict = strict;
 
     v->root = obj;

qemu/qapi/qmp-output-visitor.c

@@ -215,6 +215,13 @@ Visitor *qmp_output_get_visitor(QmpOutputVisitor *v)
     return &v->visitor;
 }
 
+static void qmp_output_free(Visitor *v)
+{
+    QmpOutputVisitor *qov = to_qov(v);
+
+    qmp_output_visitor_cleanup(qov);
+}
+
 void qmp_output_visitor_cleanup(QmpOutputVisitor *v)
 {
     QStackEntry *e, *tmp;
@@ -247,6 +254,7 @@ QmpOutputVisitor *qmp_output_visitor_new(void)
     v->visitor.type_number = qmp_output_type_number;
     v->visitor.type_any = qmp_output_type_any;
     v->visitor.type_null = qmp_output_type_null;
+    v->visitor.free = qmp_output_free;
 
     QTAILQ_INIT(&v->stack);
 

qemu/qapi/string-input-visitor.c

@@ -309,6 +309,13 @@ Visitor *string_input_get_visitor(StringInputVisitor *v)
     return &v->visitor;
 }
 
+static void string_input_free(Visitor *v)
+{
+    StringInputVisitor *siv = to_siv(v);
+
+    string_input_visitor_cleanup(siv);
+}
+
 void string_input_visitor_cleanup(StringInputVisitor *v)
 {
     g_list_foreach(v->ranges, free_range, NULL);
@@ -333,6 +340,7 @@ StringInputVisitor *string_input_visitor_new(const char *str)
     v->visitor.next_list = next_list;
     v->visitor.end_list = end_list;
     v->visitor.optional = parse_optional;
+    v->visitor.free = string_input_free;
 
     v->string = str;
     return v;

qemu/scripts/qapi-event.py

@@ -119,7 +119,7 @@ def gen_event_send(name, arg_type):
     if arg_type and arg_type.members:
         ret += mcgen('''
 out:
-    qmp_output_visitor_cleanup(qov);
+    visit_free(v);
 ''')
     ret += mcgen('''
     error_propagate(errp, err);

qemu/scripts/qapi-types.py

@@ -180,17 +180,15 @@ def gen_type_cleanup(name):
 
 void qapi_free_%(c_name)s(%(c_name)s *obj)
 {
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     if (!obj) {
         return;
     }
 
-    qdv = qapi_dealloc_visitor_new();
+    v = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
     visit_type_%(c_name)s(v, NULL, &obj, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 ''',
                 c_name=c_name(name))