[v4,1/4] QJSON: Add JSON writer

diff --git a/Makefile.objs b/Makefile.objs
index abeb902..28999d3 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -51,6 +51,7 @@  common-obj-$(CONFIG_LINUX) += fsdev/
 common-obj-y += migration/
 common-obj-y += qemu-char.o #aio.o
 common-obj-y += page_cache.o
+common-obj-y += qjson.o
 
 common-obj-$(CONFIG_SPICE) += spice-qemu-char.o
 
diff --git a/include/qjson.h b/include/qjson.h
new file mode 100644
index 0000000..7c54fdf
--- /dev/null
+++ b/include/qjson.h
@@ -0,0 +1,29 @@ 
+/*
+ * QEMU JSON writer
+ *
+ * Copyright Alexander Graf
+ *
+ * Authors:
+ *  Alexander Graf <agraf@suse.de>
+ *
+ * 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.
+ *
+ */
+#ifndef QEMU_QJSON_H
+#define QEMU_QJSON_H
+
+#define TYPE_QJSON "QJSON"
+typedef struct QJSON QJSON;
+
+QJSON *qjson_new(void);
+void json_prop_str(QJSON *json, const char *name, const char *str);
+void json_prop_int(QJSON *json, const char *name, int64_t val);
+void json_end_array(QJSON *json);
+void json_start_array(QJSON *json, const char *name);
+void json_end_object(QJSON *json);
+void json_start_object(QJSON *json, const char *name);
+const char *qjson_get_str(QJSON *json);
+void qjson_finish(QJSON *json);
+
+#endif /* QEMU_QJSON_H */
diff --git a/qjson.c b/qjson.c
new file mode 100644
index 0000000..b242222
--- /dev/null
+++ b/qjson.c
@@ -0,0 +1,129 @@ 
+/*
+ * QEMU JSON writer
+ *
+ * Copyright Alexander Graf
+ *
+ * Authors:
+ *  Alexander Graf <agraf@suse.de
+ *
+ * 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 <qapi/qmp/qstring.h>
+#include <stdbool.h>
+#include <glib.h>
+#include <qjson.h>
+#include <qemu/module.h>
+#include <qom/object.h>
+
+struct QJSON {
+    Object obj;
+    QString *str;
+    bool omit_comma;
+};
+
+static void json_emit_element(QJSON *json, const char *name)
+{
+    /* Check whether we need to print a , before an element */
+    if (json->omit_comma) {
+        json->omit_comma = false;
+    } else {
+        qstring_append(json->str, ", ");
+    }
+
+    if (name) {
+        qstring_append(json->str, "\"");
+        qstring_append(json->str, name);
+        qstring_append(json->str, "\" : ");
+    }
+}
+
+void json_start_object(QJSON *json, const char *name)
+{
+    json_emit_element(json, name);
+    qstring_append(json->str, "{ ");
+    json->omit_comma = true;
+}
+
+void json_end_object(QJSON *json)
+{
+    qstring_append(json->str, " }");
+    json->omit_comma = false;
+}
+
+void json_start_array(QJSON *json, const char *name)
+{
+    json_emit_element(json, name);
+    qstring_append(json->str, "[ ");
+    json->omit_comma = true;
+}
+
+void json_end_array(QJSON *json)
+{
+    qstring_append(json->str, " ]");
+    json->omit_comma = false;
+}
+
+void json_prop_int(QJSON *json, const char *name, int64_t val)
+{
+    json_emit_element(json, name);
+    qstring_append_int(json->str, val);
+}
+
+void json_prop_str(QJSON *json, const char *name, const char *str)
+{
+    json_emit_element(json, name);
+    qstring_append_chr(json->str, '"');
+    qstring_append(json->str, str);
+    qstring_append_chr(json->str, '"');
+}
+
+const char *qjson_get_str(QJSON *json)
+{
+    return qstring_get_str(json->str);
+}
+
+QJSON *qjson_new(void)
+{
+    QJSON *json = (QJSON *)object_new(TYPE_QJSON);
+    return json;
+}
+
+void qjson_finish(QJSON *json)
+{
+    json_end_object(json);
+}
+
+static void qjson_initfn(Object *obj)
+{
+    QJSON *json = (QJSON *)object_dynamic_cast(obj, TYPE_QJSON);
+    assert(json);
+
+    json->str = qstring_from_str("{ ");
+    json->omit_comma = true;
+}
+
+static void qjson_finalizefn(Object *obj)
+{
+    QJSON *json = (QJSON *)object_dynamic_cast(obj, TYPE_QJSON);
+
+    assert(json);
+    qobject_decref(QOBJECT(json->str));
+}
+
+static const TypeInfo qjson_type_info = {
+    .name = TYPE_QJSON,
+    .parent = TYPE_OBJECT,
+    .instance_size = sizeof(QJSON),
+    .instance_init = qjson_initfn,
+    .instance_finalize = qjson_finalizefn,
+};
+
+static void qjson_register_types(void)
+{
+    type_register_static(&qjson_type_info);
+}
+
+type_init(qjson_register_types)