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);
|}

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1465490926-28625-5-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/qapi-code-gen.txt

@@ -802,32 +802,28 @@ Example:
 
     void qapi_free_UserDefOne(UserDefOne *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_UserDefOne(v, NULL, &obj, NULL);
-        qapi_dealloc_visitor_cleanup(qdv);
+        visit_free(v);
     }
 
     void qapi_free_UserDefOneList(UserDefOneList *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_UserDefOneList(v, NULL, &obj, NULL);
-        qapi_dealloc_visitor_cleanup(qdv);
+        visit_free(v);
     }
 
 === scripts/qapi-visit.py ===
@@ -985,7 +981,6 @@ Example:
     {
         Error *err = NULL;
         QmpOutputVisitor *qov = qmp_output_visitor_new();
-        QapiDeallocVisitor *qdv;
         Visitor *v;
 
         v = qmp_output_get_visitor(qov);
@@ -997,19 +992,17 @@ Example:
 
     out:
         error_propagate(errp, err);
-        qmp_output_visitor_cleanup(qov);
-        qdv = qapi_dealloc_visitor_new();
-        v = qapi_dealloc_get_visitor(qdv);
+        visit_free(v);
+        v = qapi_dealloc_visitor_new();
         visit_type_UserDefOne(v, "unused", &ret_in, NULL);
-        qapi_dealloc_visitor_cleanup(qdv);
+        visit_free(v);
     }
 
     static void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp)
     {
         Error *err = NULL;
         UserDefOne *retval;
         QmpInputVisitor *qiv = qmp_input_visitor_new(QOBJECT(args), true);
-        QapiDeallocVisitor *qdv;
         Visitor *v;
         UserDefOneList *arg1 = NULL;
 
@@ -1036,13 +1029,12 @@ Example:
 
     out:
         error_propagate(errp, err);
-        qmp_input_visitor_cleanup(qiv);
-        qdv = qapi_dealloc_visitor_new();
-        v = qapi_dealloc_get_visitor(qdv);
+        visit_free(v);
+        v = qapi_dealloc_visitor_new();
         visit_start_struct(v, NULL, NULL, 0, NULL);
         visit_type_UserDefOneList(v, "arg1", &arg1, NULL);
         visit_end_struct(v, NULL);
-        qapi_dealloc_visitor_cleanup(qdv);
+        visit_free(v);
     }
 
     static void qmp_init_marshal(void)

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);
-void qapi_dealloc_visitor_cleanup(QapiDeallocVisitor *d);
-
-Visitor *qapi_dealloc_get_visitor(QapiDeallocVisitor *v);
+Visitor *qapi_dealloc_visitor_new(void);
 
 #endif

include/qapi/visitor-impl.h

@@ -104,6 +104,9 @@ struct Visitor
 
     /* Must be set */
     VisitorType type;
+
+    /* Must be set */
+    void (*free)(Visitor *v);
 };
 
 #endif

include/qapi/visitor.h

@@ -37,6 +37,24 @@
  * 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:
  *
@@ -222,6 +240,19 @@ 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 ***/
 
 /*
@@ -272,7 +303,7 @@ 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);
 
@@ -332,7 +363,7 @@ 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);
 
@@ -368,7 +399,7 @@ 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);

qapi/opts-visitor.c

@@ -513,6 +513,15 @@ opts_optional(Visitor *v, const char *name, bool *present)
 }
 
 
+static void
+opts_free(Visitor *v)
+{
+    OptsVisitor *ov = to_ov(v);
+
+    opts_visitor_cleanup(ov);
+}
+
+
 OptsVisitor *
 opts_visitor_new(const QemuOpts *opts)
 {
@@ -540,6 +549,7 @@ opts_visitor_new(const QemuOpts *opts)
      * skip some mandatory methods... */
 
     ov->visitor.optional = &opts_optional;
+    ov->visitor.free = opts_free;
 
     ov->opts_root = opts;
 

qapi/qapi-dealloc-visitor.c

@@ -107,17 +107,12 @@ 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)
-{
-    g_free(v);
-}
-
-QapiDeallocVisitor *qapi_dealloc_visitor_new(void)
+Visitor *qapi_dealloc_visitor_new(void)
 {
     QapiDeallocVisitor *v;
 
@@ -138,6 +133,7 @@ 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.free = qapi_dealloc_free;
 
-    return v;
+    return &v->visitor;
 }

qapi/qapi-visit-core.c

@@ -20,6 +20,13 @@
 #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)
 {

qapi/qmp-input-visitor.c

@@ -378,6 +378,13 @@ 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);
@@ -406,6 +413,7 @@ 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;

qapi/qmp-output-visitor.c

@@ -214,6 +214,13 @@ 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;
@@ -246,6 +253,7 @@ 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);
 

qapi/string-input-visitor.c

@@ -331,6 +331,13 @@ 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);
@@ -355,6 +362,7 @@ 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;

qapi/string-output-visitor.c

@@ -322,6 +322,13 @@ static void free_range(void *range, void *dummy)
     g_free(range);
 }
 
+static void string_output_free(Visitor *v)
+{
+    StringOutputVisitor *sov = to_sov(v);
+
+    string_output_visitor_cleanup(sov);
+}
+
 void string_output_visitor_cleanup(StringOutputVisitor *sov)
 {
     if (sov->string) {
@@ -351,6 +358,7 @@ StringOutputVisitor *string_output_visitor_new(bool human)
     v->visitor.start_list = start_list;
     v->visitor.next_list = next_list;
     v->visitor.end_list = end_list;
+    v->visitor.free = string_output_free;
 
     return v;
 }

scripts/qapi-commands.py

@@ -62,7 +62,6 @@ def gen_marshal_output(ret_type):
 {
     Error *err = NULL;
     QmpOutputVisitor *qov = qmp_output_visitor_new();
-    QapiDeallocVisitor *qdv;
     Visitor *v;
 
     v = qmp_output_get_visitor(qov);
@@ -74,11 +73,10 @@ def gen_marshal_output(ret_type):
 
 out:
     error_propagate(errp, err);
-    qmp_output_visitor_cleanup(qov);
-    qdv = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
+    visit_free(v);
+    v = qapi_dealloc_visitor_new();
     visit_type_%(c_name)s(v, "unused", &ret_in, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 }
 ''',
                  c_type=ret_type.c_type(), c_name=ret_type.c_name())
@@ -116,7 +114,6 @@ def gen_marshal(name, arg_type, ret_type):
     if arg_type and arg_type.members:
         ret += mcgen('''
     QmpInputVisitor *qiv = qmp_input_visitor_new(QOBJECT(args), true);
-    QapiDeallocVisitor *qdv;
     Visitor *v;
     %(c_name)s arg = {0};
 
@@ -155,13 +152,12 @@ def gen_marshal(name, arg_type, ret_type):
 ''')
     if arg_type and arg_type.members:
         ret += mcgen('''
-    qmp_input_visitor_cleanup(qiv);
-    qdv = qapi_dealloc_visitor_new();
-    v = qapi_dealloc_get_visitor(qdv);
+    visit_free(v);
+    v = qapi_dealloc_visitor_new();
     visit_start_struct(v, NULL, NULL, 0, NULL);
     visit_type_%(c_name)s_members(v, &arg, NULL);
     visit_end_struct(v, NULL);
-    qapi_dealloc_visitor_cleanup(qdv);
+    visit_free(v);
 ''',
                      c_name=arg_type.c_name())
 

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);