qapi: introduce forwarding visitor

This new adaptor visitor takes a single field of the adaptee, and exposes it
with a different name.

This will be used for QOM alias properties.  Alias targets can of course
have a different name than the alias property itself (e.g. a machine's
pflash0 might be an alias of a property named 'drive').  When the target's
getter or setter invokes the visitor, it will use a different name than
what the caller expects, and the visitor will not be able to find it
(or will consume erroneously).

The solution is for alias getters and setters to wrap the incoming
visitor, and forward the sole field that the target is expecting while
renaming it appropriately.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 326 insertions, 0 deletions

diff --git a/qapi/qapi-forward-visitor.c b/qapi/qapi-forward-visitor.c
new file mode 100644
index 0000000000..a4b111e22a
--- /dev/null
+++ b/qapi/qapi-forward-visitor.c
@@ -0,0 +1,326 @@
+/*
+ * Forward Visitor
+ *
+ * Copyright (C) 2021 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/compat-policy.h"
+#include "qapi/error.h"
+#include "qapi/forward-visitor.h"
+#include "qapi/visitor-impl.h"
+#include "qemu/queue.h"
+#include "qapi/qmp/qjson.h"
+#include "qapi/qmp/qbool.h"
+#include "qapi/qmp/qdict.h"
+#include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qlist.h"
+#include "qapi/qmp/qnull.h"
+#include "qapi/qmp/qnum.h"
+#include "qapi/qmp/qstring.h"
+#include "qemu/cutils.h"
+#include "qemu/option.h"
+
+struct ForwardFieldVisitor {
+    Visitor visitor;
+
+    Visitor *target;
+    char *from;
+    char *to;
+
+    int depth;
+};
+
+static ForwardFieldVisitor *to_ffv(Visitor *v)
+{
+    return container_of(v, ForwardFieldVisitor, visitor);
+}
+
+static bool forward_field_translate_name(ForwardFieldVisitor *v, const char **name,
+                                         Error **errp)
+{
+    if (v->depth) {
+        return true;
+    }
+    if (g_str_equal(*name, v->from)) {
+        *name = v->to;
+        return true;
+    }
+    error_setg(errp, QERR_MISSING_PARAMETER, *name);
+    return false;
+}
+
+static bool forward_field_check_struct(Visitor *v, Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    return visit_check_struct(ffv->target, errp);
+}
+
+static bool forward_field_start_struct(Visitor *v, const char *name, void **obj,
+                                       size_t size, Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    if (!visit_start_struct(ffv->target, name, obj, size, errp)) {
+        return false;
+    }
+    ffv->depth++;
+    return true;
+}
+
+static void forward_field_end_struct(Visitor *v, void **obj)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    assert(ffv->depth);
+    ffv->depth--;
+    visit_end_struct(ffv->target, obj);
+}
+
+static bool forward_field_start_list(Visitor *v, const char *name,
+                                     GenericList **list, size_t size,
+                                     Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    ffv->depth++;
+    return visit_start_list(ffv->target, name, list, size, errp);
+}
+
+static GenericList *forward_field_next_list(Visitor *v, GenericList *tail,
+                                            size_t size)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    assert(ffv->depth);
+    return visit_next_list(ffv->target, tail, size);
+}
+
+static bool forward_field_check_list(Visitor *v, Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    assert(ffv->depth);
+    return visit_check_list(ffv->target, errp);
+}
+
+static void forward_field_end_list(Visitor *v, void **obj)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    assert(ffv->depth);
+    ffv->depth--;
+    visit_end_list(ffv->target, obj);
+}
+
+static bool forward_field_start_alternate(Visitor *v, const char *name,
+                                          GenericAlternate **obj, size_t size,
+                                          Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    /*
+     * The name passed to start_alternate is used also in the visit_type_* calls
+     * that retrieve the alternate's content; so, do not increase depth here.
+     */
+    return visit_start_alternate(ffv->target, name, obj, size, errp);
+}
+
+static void forward_field_end_alternate(Visitor *v, void **obj)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    visit_end_alternate(ffv->target, obj);
+}
+
+static bool forward_field_type_int64(Visitor *v, const char *name, int64_t *obj,
+                                     Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_type_int64(ffv->target, name, obj, errp);
+}
+
+static bool forward_field_type_uint64(Visitor *v, const char *name,
+                                      uint64_t *obj, Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_type_uint64(ffv->target, name, obj, errp);
+}
+
+static bool forward_field_type_bool(Visitor *v, const char *name, bool *obj,
+                                    Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_type_bool(ffv->target, name, obj, errp);
+}
+
+static bool forward_field_type_str(Visitor *v, const char *name, char **obj,
+                                   Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_type_str(ffv->target, name, obj, errp);
+}
+
+static bool forward_field_type_size(Visitor *v, const char *name, uint64_t *obj,
+                                    Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_type_size(ffv->target, name, obj, errp);
+}
+
+static bool forward_field_type_number(Visitor *v, const char *name, double *obj,
+                                      Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_type_number(ffv->target, name, obj, errp);
+}
+
+static bool forward_field_type_any(Visitor *v, const char *name, QObject **obj,
+                                   Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_type_any(ffv->target, name, obj, errp);
+}
+
+static bool forward_field_type_null(Visitor *v, const char *name,
+                                    QNull **obj, Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_type_null(ffv->target, name, obj, errp);
+}
+
+static void forward_field_optional(Visitor *v, const char *name, bool *present)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, NULL)) {
+        *present = false;
+        return;
+    }
+    visit_optional(ffv->target, name, present);
+}
+
+static bool forward_field_deprecated_accept(Visitor *v, const char *name,
+                                            Error **errp)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, errp)) {
+        return false;
+    }
+    return visit_deprecated_accept(ffv->target, name, errp);
+}
+
+static bool forward_field_deprecated(Visitor *v, const char *name)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    if (!forward_field_translate_name(ffv, &name, NULL)) {
+        return false;
+    }
+    return visit_deprecated(ffv->target, name);
+}
+
+static void forward_field_complete(Visitor *v, void *opaque)
+{
+    /*
+     * Do nothing, the complete method will be called in due time
+     * on the target visitor.
+     */
+}
+
+static void forward_field_free(Visitor *v)
+{
+    ForwardFieldVisitor *ffv = to_ffv(v);
+
+    g_free(ffv->from);
+    g_free(ffv->to);
+    g_free(ffv);
+}
+
+Visitor *visitor_forward_field(Visitor *target, const char *from, const char *to)
+{
+    ForwardFieldVisitor *v = g_new0(ForwardFieldVisitor, 1);
+
+    /*
+     * Clone and dealloc visitors don't use a name for the toplevel
+     * visit, so they make no sense here.
+     */
+    assert(target->type == VISITOR_OUTPUT || target->type == VISITOR_INPUT);
+
+    v->visitor.type = target->type;
+    v->visitor.start_struct = forward_field_start_struct;
+    v->visitor.check_struct = forward_field_check_struct;
+    v->visitor.end_struct = forward_field_end_struct;
+    v->visitor.start_list = forward_field_start_list;
+    v->visitor.next_list = forward_field_next_list;
+    v->visitor.check_list = forward_field_check_list;
+    v->visitor.end_list = forward_field_end_list;
+    v->visitor.start_alternate = forward_field_start_alternate;
+    v->visitor.end_alternate = forward_field_end_alternate;
+    v->visitor.type_int64 = forward_field_type_int64;
+    v->visitor.type_uint64 = forward_field_type_uint64;
+    v->visitor.type_size = forward_field_type_size;
+    v->visitor.type_bool = forward_field_type_bool;
+    v->visitor.type_str = forward_field_type_str;
+    v->visitor.type_number = forward_field_type_number;
+    v->visitor.type_any = forward_field_type_any;
+    v->visitor.type_null = forward_field_type_null;
+    v->visitor.optional = forward_field_optional;
+    v->visitor.deprecated_accept = forward_field_deprecated_accept;
+    v->visitor.deprecated = forward_field_deprecated;
+    v->visitor.complete = forward_field_complete;
+    v->visitor.free = forward_field_free;
+
+    v->target = target;
+    v->from = g_strdup(from);
+    v->to = g_strdup(to);
+
+    return &v->visitor;
+}