[v2,1/4] qapi: Add visit_type_str_preserving()

diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index 2badec5ba460..7b61f55995b5 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -95,7 +95,8 @@  struct Visitor
     bool (*type_bool)(Visitor *v, const char *name, bool *obj, Error **errp);
 
     /* Must be set */
-    bool (*type_str)(Visitor *v, const char *name, char **obj, Error **errp);
+    bool (*type_str)(Visitor *v, const char *name, char **obj, bool consume,
+                     Error **errp);
 
     /* Must be set to visit numbers */
     bool (*type_number)(Visitor *v, const char *name, double *obj,
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index 27b85d4700f2..b3ae3188edfb 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -654,6 +654,26 @@  bool visit_type_bool(Visitor *v, const char *name, bool *obj, Error **errp);
  */
 bool visit_type_str(Visitor *v, const char *name, char **obj, Error **errp);
 
+/*
+ * Visit a string value but do not consume it.
+ *
+ * @name expresses the relationship of this string to its parent
+ * container; see the general description of @name above.
+ *
+ * @obj must be non-NULL.  Input and clone visitors set *@obj to the
+ * value (always using "" rather than NULL for an empty string).
+ * Other visitors leave *@obj unchanged, and commonly treat NULL like
+ * "".
+ *
+ * This function must be called only with an input visitor.
+ *
+ * This is mostly identical with visit_type_str() but leaves the value intact.
+ * This is useful when the caller may interpret the value with a different
+ * type.
+ */
+bool visit_type_str_preserving(Visitor *v, const char *name, char **obj,
+                               Error **errp);
+
 /*
  * Visit a number (i.e. double) value.
  *
diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
index 3d1a28b41918..e9fad756e189 100644
--- a/qapi/opts-visitor.c
+++ b/qapi/opts-visitor.c
@@ -347,7 +347,8 @@  processed(OptsVisitor *ov, const char *name)
 
 
 static bool
-opts_type_str(Visitor *v, const char *name, char **obj, Error **errp)
+opts_type_str(Visitor *v, const char *name, char **obj, bool consume,
+              Error **errp)
 {
     OptsVisitor *ov = to_ov(v);
     const QemuOpt *opt;
@@ -363,7 +364,9 @@  opts_type_str(Visitor *v, const char *name, char **obj, Error **errp)
      * valid enum value; this is harmless because tracking what gets
      * consumed only matters to visit_end_struct() as the final error
      * check if there were no other failures during the visit.  */
-    processed(ov, name);
+    if (consume) {
+        processed(ov, name);
+    }
     return true;
 }
 
diff --git a/qapi/qapi-clone-visitor.c b/qapi/qapi-clone-visitor.c
index bbf953698f38..90e6641835a7 100644
--- a/qapi/qapi-clone-visitor.c
+++ b/qapi/qapi-clone-visitor.c
@@ -108,7 +108,7 @@  static bool qapi_clone_type_bool(Visitor *v, const char *name, bool *obj,
 }
 
 static bool qapi_clone_type_str(Visitor *v, const char *name, char **obj,
-                                Error **errp)
+                                bool consume, Error **errp)
 {
     QapiCloneVisitor *qcv = to_qcv(v);
 
diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c
index ef283f296601..6b0f957047d5 100644
--- a/qapi/qapi-dealloc-visitor.c
+++ b/qapi/qapi-dealloc-visitor.c
@@ -62,9 +62,9 @@  static void qapi_dealloc_end_list(Visitor *v, void **obj)
 }
 
 static bool qapi_dealloc_type_str(Visitor *v, const char *name, char **obj,
-                                  Error **errp)
+                                  bool consume, Error **errp)
 {
-    if (obj) {
+    if (obj && consume) {
         g_free(*obj);
     }
     return true;
diff --git a/qapi/qapi-forward-visitor.c b/qapi/qapi-forward-visitor.c
index e36d9bc9ba7e..891282e0c3b3 100644
--- a/qapi/qapi-forward-visitor.c
+++ b/qapi/qapi-forward-visitor.c
@@ -180,6 +180,7 @@  static bool forward_field_type_bool(Visitor *v, const char *name, bool *obj,
 }
 
 static bool forward_field_type_str(Visitor *v, const char *name, char **obj,
+                                   bool consume,
                                    Error **errp)
 {
     ForwardFieldVisitor *ffv = to_ffv(v);
@@ -187,7 +188,8 @@  static bool forward_field_type_str(Visitor *v, const char *name, char **obj,
     if (!forward_field_translate_name(ffv, &name, errp)) {
         return false;
     }
-    return visit_type_str(ffv->target, name, obj, errp);
+    return (consume ? visit_type_str : visit_type_str_preserving)(
+        ffv->target, name, obj, errp);
 }
 
 static bool forward_field_type_size(Visitor *v, const char *name, uint64_t *obj,
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 6c13510a2bc7..89b52fc99202 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -336,7 +336,8 @@  bool visit_type_bool(Visitor *v, const char *name, bool *obj, Error **errp)
     return v->type_bool(v, name, obj, errp);
 }
 
-bool visit_type_str(Visitor *v, const char *name, char **obj, Error **errp)
+static bool visit_type_str_common(Visitor *v, const char *name, char **obj,
+                                  bool consume, Error **errp)
 {
     bool ok;
 
@@ -346,13 +347,25 @@  bool visit_type_str(Visitor *v, const char *name, char **obj, Error **errp)
     assert(!(v->type & VISITOR_OUTPUT) || *obj);
      */
     trace_visit_type_str(v, name, obj);
-    ok = v->type_str(v, name, obj, errp);
+    ok = v->type_str(v, name, obj, consume, errp);
     if (v->type & VISITOR_INPUT) {
         assert(ok != !*obj);
     }
     return ok;
 }
 
+bool visit_type_str(Visitor *v, const char *name, char **obj, Error **errp)
+{
+    return visit_type_str_common(v, name, obj, true, errp);
+}
+
+bool visit_type_str_preserving(Visitor *v, const char *name, char **obj,
+                               Error **errp)
+{
+    assert(v->type & VISITOR_INPUT);
+    return visit_type_str_common(v, name, obj, false, errp);
+}
+
 bool visit_type_number(Visitor *v, const char *name, double *obj,
                        Error **errp)
 {
diff --git a/qapi/qobject-input-visitor.c b/qapi/qobject-input-visitor.c
index f110a804b2ae..facbbf01bd27 100644
--- a/qapi/qobject-input-visitor.c
+++ b/qapi/qobject-input-visitor.c
@@ -174,13 +174,13 @@  static QObject *qobject_input_get_object(QObjectInputVisitor *qiv,
 }
 
 static const char *qobject_input_get_keyval(QObjectInputVisitor *qiv,
-                                            const char *name,
+                                            const char *name, bool consume,
                                             Error **errp)
 {
     QObject *qobj;
     QString *qstr;
 
-    qobj = qobject_input_get_object(qiv, name, true, errp);
+    qobj = qobject_input_get_object(qiv, name, consume, errp);
     if (!qobj) {
         return NULL;
     }
@@ -416,7 +416,7 @@  static bool qobject_input_type_int64_keyval(Visitor *v, const char *name,
                                             int64_t *obj, Error **errp)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
-    const char *str = qobject_input_get_keyval(qiv, name, errp);
+    const char *str = qobject_input_get_keyval(qiv, name, true, errp);
 
     if (!str) {
         return false;
@@ -467,7 +467,7 @@  static bool qobject_input_type_uint64_keyval(Visitor *v, const char *name,
                                              uint64_t *obj, Error **errp)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
-    const char *str = qobject_input_get_keyval(qiv, name, errp);
+    const char *str = qobject_input_get_keyval(qiv, name, true, errp);
 
     if (!str) {
         return false;
@@ -507,7 +507,7 @@  static bool qobject_input_type_bool_keyval(Visitor *v, const char *name,
                                            bool *obj, Error **errp)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
-    const char *str = qobject_input_get_keyval(qiv, name, errp);
+    const char *str = qobject_input_get_keyval(qiv, name, true, errp);
 
     if (!str) {
         return false;
@@ -522,10 +522,10 @@  static bool qobject_input_type_bool_keyval(Visitor *v, const char *name,
 }
 
 static bool qobject_input_type_str(Visitor *v, const char *name, char **obj,
-                                   Error **errp)
+                                   bool consume, Error **errp)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
-    QObject *qobj = qobject_input_get_object(qiv, name, true, errp);
+    QObject *qobj = qobject_input_get_object(qiv, name, consume, errp);
     QString *qstr;
 
     *obj = NULL;
@@ -544,10 +544,11 @@  static bool qobject_input_type_str(Visitor *v, const char *name, char **obj,
 }
 
 static bool qobject_input_type_str_keyval(Visitor *v, const char *name,
-                                          char **obj, Error **errp)
+                                          char **obj, bool consume,
+                                          Error **errp)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
-    const char *str = qobject_input_get_keyval(qiv, name, errp);
+    const char *str = qobject_input_get_keyval(qiv, name, consume, errp);
 
     *obj = g_strdup(str);
     return !!str;
@@ -578,7 +579,7 @@  static bool qobject_input_type_number_keyval(Visitor *v, const char *name,
                                              double *obj, Error **errp)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
-    const char *str = qobject_input_get_keyval(qiv, name, errp);
+    const char *str = qobject_input_get_keyval(qiv, name, true, errp);
     double val;
 
     if (!str) {
@@ -635,7 +636,7 @@  static bool qobject_input_type_size_keyval(Visitor *v, const char *name,
                                            uint64_t *obj, Error **errp)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
-    const char *str = qobject_input_get_keyval(qiv, name, errp);
+    const char *str = qobject_input_get_keyval(qiv, name, true, errp);
 
     if (!str) {
         return false;
diff --git a/qapi/qobject-output-visitor.c b/qapi/qobject-output-visitor.c
index 74770edd73c6..36a9fc245b79 100644
--- a/qapi/qobject-output-visitor.c
+++ b/qapi/qobject-output-visitor.c
@@ -173,7 +173,7 @@  static bool qobject_output_type_bool(Visitor *v, const char *name, bool *obj,
 }
 
 static bool qobject_output_type_str(Visitor *v, const char *name, char **obj,
-                                    Error **errp)
+                                    bool consume, Error **errp)
 {
     QObjectOutputVisitor *qov = to_qov(v);
     if (*obj) {
diff --git a/qapi/string-input-visitor.c b/qapi/string-input-visitor.c
index 3f1b9e9b4137..6562bbe3cfd4 100644
--- a/qapi/string-input-visitor.c
+++ b/qapi/string-input-visitor.c
@@ -336,7 +336,7 @@  static bool parse_type_bool(Visitor *v, const char *name, bool *obj,
 }
 
 static bool parse_type_str(Visitor *v, const char *name, char **obj,
-                           Error **errp)
+                           bool consume, Error **errp)
 {
     StringInputVisitor *siv = to_siv(v);
 
diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c
index 5115536b1539..9a8cca0d5c68 100644
--- a/qapi/string-output-visitor.c
+++ b/qapi/string-output-visitor.c
@@ -269,7 +269,7 @@  static bool print_type_bool(Visitor *v, const char *name, bool *obj,
 }
 
 static bool print_type_str(Visitor *v, const char *name, char **obj,
-                           Error **errp)
+                           bool consume, Error **errp)
 {
     StringOutputVisitor *sov = to_sov(v);
     char *out;