add memdev backend infrastructure

Provides framework for splitting host RAM allocation/
policies into a separate backend that could be used
by devices.

Initially only legacy RAM backend is provided, which
uses memory_region_init_ram() allocator and compatible
with every CLI option that affects memory_region_init_ram().

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

backends/hostmem.c

@@ -0,0 +1,97 @@
+/*
+ * QEMU Host Memory Backend
+ *
+ * Copyright (C) 2013-2014 Red Hat Inc
+ *
+ * Authors:
+ *   Igor Mammedov <imammedo@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+#include "sysemu/hostmem.h"
+#include "sysemu/sysemu.h"
+#include "qapi/visitor.h"
+#include "qapi/qmp/qerror.h"
+#include "qemu/config-file.h"
+#include "qom/object_interfaces.h"
+
+static void
+hostmemory_backend_get_size(Object *obj, Visitor *v, void *opaque,
+                            const char *name, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+    uint64_t value = backend->size;
+
+    visit_type_size(v, &value, name, errp);
+}
+
+static void
+hostmemory_backend_set_size(Object *obj, Visitor *v, void *opaque,
+                            const char *name, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+    Error *local_err = NULL;
+    uint64_t value;
+
+    if (memory_region_size(&backend->mr)) {
+        error_setg(&local_err, "cannot change property value");
+        goto out;
+    }
+
+    visit_type_size(v, &value, name, &local_err);
+    if (local_err) {
+        goto out;
+    }
+    if (!value) {
+        error_setg(&local_err, "Property '%s.%s' doesn't take value '%"
+                   PRIu64 "'", object_get_typename(obj), name, value);
+        goto out;
+    }
+    backend->size = value;
+out:
+    error_propagate(errp, local_err);
+}
+
+static void hostmemory_backend_init(Object *obj)
+{
+    object_property_add(obj, "size", "int",
+                        hostmemory_backend_get_size,
+                        hostmemory_backend_set_size, NULL, NULL, NULL);
+}
+
+static void hostmemory_backend_finalize(Object *obj)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+
+    if (memory_region_size(&backend->mr)) {
+        memory_region_destroy(&backend->mr);
+    }
+}
+
+MemoryRegion *
+host_memory_backend_get_memory(HostMemoryBackend *backend, Error **errp)
+{
+    return memory_region_size(&backend->mr) ? &backend->mr : NULL;
+}
+
+static const TypeInfo hostmemory_backend_info = {
+    .name = TYPE_MEMORY_BACKEND,
+    .parent = TYPE_OBJECT,
+    .abstract = true,
+    .class_size = sizeof(HostMemoryBackendClass),
+    .instance_size = sizeof(HostMemoryBackend),
+    .instance_init = hostmemory_backend_init,
+    .instance_finalize = hostmemory_backend_finalize,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_USER_CREATABLE },
+        { }
+    }
+};
+
+static void register_types(void)
+{
+    type_register_static(&hostmemory_backend_info);
+}
+
+type_init(register_types);