[Qemu-devel] [PATCH 1/5] qom: add a generic mechanism to resolve paths

[Paolo Bonzini <pbonzini@redhat.com>]

It may be desirable to have custom link<> properties that do more
than just store an object.  Even the addition of a "check"
function is not enough if setting the link has side effects
or if a non-standard reference counting is preferrable.

Avoid the assumption that the opaque field of a link<> is a
LinkProperty struct, by adding a generic "resolve" callback
to ObjectProperty.  This fixes aliases of link properties.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 include/qom/object.h | 49 ++++++++++++++++++++++++++++++++++++++++++++++
 qom/object.c         | 55 ++++++++++++++++++++++++++++++++++------------------
 2 files changed, 85 insertions(+), 19 deletions(-)

diff --git a/include/qom/object.h b/include/qom/object.h
index a641dcd..f8ab845 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -304,6 +304,23 @@ typedef void (ObjectPropertyAccessor)(Object *obj,
                                       Error **errp);
 
 /**
+ * ObjectPropertyResolve:
+ * @obj: the object that owns the property
+ * @opaque: the opaque registered with the property
+ * @part: the name of the property
+ *
+ * If @path is the path that led to @obj, the function should
+ * return the Object corresponding to "@path/@part".  If #NULL
+ * is returned, "@path/@part" is not a valid object path.
+ *
+ * The returned object can also be used as a starting point
+ * to resolve a relative path starting with "@part".
+ */
+typedef Object *(ObjectPropertyResolve)(Object *obj,
+                                        void *opaque,
+                                        const char *part);
+
+/**
  * ObjectPropertyRelease:
  * @obj: the object that owns the property
  * @name: the name of the property
@@ -321,6 +338,7 @@ typedef struct ObjectProperty
     gchar *type;
     ObjectPropertyAccessor *get;
     ObjectPropertyAccessor *set;
+    ObjectPropertyResolve *resolve;
     ObjectPropertyRelease *release;
     void *opaque;
 
@@ -769,6 +787,37 @@ void object_ref(Object *obj);
 void object_unref(Object *obj);
 
 /**
+ * object_property_add_full:
+ * @obj: the object to add a property to
+ * @name: the name of the property.  This can contain any character except for
+ *  a forward slash.  In general, you should use hyphens '-' instead of
+ *  underscores '_' when naming properties.
+ * @type: the type name of the property.  This namespace is pretty loosely
+ *   defined.  Sub namespaces are constructed by using a prefix and then
+ *   to angle brackets.  For instance, the type 'virtio-net-pci' in the
+ *   'link' namespace would be 'link<virtio-net-pci>'.
+ * @get: The getter to be called to read a property.  If this is NULL, then
+ *   the property cannot be read.
+ * @set: the setter to be called to write a property.  If this is NULL,
+ *   then the property cannot be written.
+ * @resolve: called when the property name is used as part of an object
+ *   path.  This is meant for cases when you want to have custom link
+ *   properties.  If it is NULL, the property name cannot be used as part
+ *   of a valid object path.
+ * @release: called when the property is removed from the object.  This is
+ *   meant to allow a property to free its opaque upon object
+ *   destruction.  This may be NULL.
+ * @opaque: an opaque pointer to pass to the callbacks for the property
+ * @errp: returns an error if this function fails
+ */
+void object_property_add_full(Object *obj, const char *name, const char *type,
+                              ObjectPropertyAccessor *get,
+                              ObjectPropertyAccessor *set,
+                              ObjectPropertyResolve *resolve,
+                              ObjectPropertyRelease *release,
+                              void *opaque, Error **errp);
+
+/**
  * object_property_add:
  * @obj: the object to add a property to
  * @name: the name of the property.  This can contain any character except for
diff --git a/qom/object.c b/qom/object.c
index e42b254..fcdd0da 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -355,11 +355,6 @@ static inline bool object_property_is_child(ObjectProperty *prop)
     return strstart(prop->type, "child<", NULL);
 }
 
-static inline bool object_property_is_link(ObjectProperty *prop)
-{
-    return strstart(prop->type, "link<", NULL);
-}
-
 static void object_property_del_all(Object *obj)
 {
     while (!QTAILQ_EMPTY(&obj->properties)) {
@@ -727,9 +722,10 @@ void object_unref(Object *obj)
     }
 }
 
-void object_property_add(Object *obj, const char *name, const char *type,
+void object_property_add_full(Object *obj, const char *name, const char *type,
                          ObjectPropertyAccessor *get,
                          ObjectPropertyAccessor *set,
+                         ObjectPropertyResolve *resolve,
                          ObjectPropertyRelease *release,
                          void *opaque, Error **errp)
 {
@@ -751,12 +747,23 @@ void object_property_add(Object *obj, const char *name, const char *type,
 
     prop->get = get;
     prop->set = set;
+    prop->resolve = resolve;
     prop->release = release;
     prop->opaque = opaque;
 
     QTAILQ_INSERT_TAIL(&obj->properties, prop, node);
 }
 
+void object_property_add(Object *obj, const char *name, const char *type,
+                         ObjectPropertyAccessor *get,
+                         ObjectPropertyAccessor *set,
+                         ObjectPropertyRelease *release,
+                         void *opaque, Error **errp)
+{
+    object_property_add_full(obj, name, type, get, set, NULL, release,
+                             opaque, errp);
+}
+
 ObjectProperty *object_property_find(Object *obj, const char *name,
                                      Error **errp)
 {
@@ -993,6 +1000,11 @@ static void object_get_child_property(Object *obj, Visitor *v, void *opaque,
     g_free(path);
 }
 
+static Object *object_resolve_child_property(Object *parent, void *opaque, const gchar *part)
+{
+    return opaque;
+}
+
 static void object_finalize_child_property(Object *obj, const char *name,
                                            void *opaque)
 {
@@ -1009,8 +1021,9 @@ void object_property_add_child(Object *obj, const char *name,
 
     type = g_strdup_printf("child<%s>", object_get_typename(OBJECT(child)));
 
-    object_property_add(obj, name, type, object_get_child_property, NULL,
-                        object_finalize_child_property, child, &local_err);
+    object_property_add_full(obj, name, type, object_get_child_property, NULL,
+                             object_resolve_child_property,
+                             object_finalize_child_property, child, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         goto out;
@@ -1128,6 +1141,12 @@ static void object_set_link_property(Object *obj, Visitor *v, void *opaque,
     }
 }
 
+static Object *object_resolve_link_property(Object *parent, void *opaque, const gchar *part)
+{
+    LinkProperty *lprop = opaque;
+    return *lprop->child;
+}
+
 static void object_release_link_property(Object *obj, const char *name,
                                          void *opaque)
 {
@@ -1156,12 +1175,13 @@ void object_property_add_link(Object *obj, const char *name,
 
     full_type = g_strdup_printf("link<%s>", type);
 
-    object_property_add(obj, name, full_type,
-                        object_get_link_property,
-                        check ? object_set_link_property : NULL,
-                        object_release_link_property,
-                        prop,
-                        &local_err);
+    object_property_add_full(obj, name, full_type,
+                             object_get_link_property,
+                             check ? object_set_link_property : NULL,
+                             object_resolve_link_property,
+                             object_release_link_property,
+                             prop,
+                             &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         g_free(prop);
@@ -1225,11 +1245,8 @@ Object *object_resolve_path_component(Object *parent, const gchar *part)
         return NULL;
     }
 
-    if (object_property_is_link(prop)) {
-        LinkProperty *lprop = prop->opaque;
-        return *lprop->child;
-    } else if (object_property_is_child(prop)) {
-        return prop->opaque;
+    if (prop->resolve) {
+        return prop->resolve(parent, prop->opaque, part);
     } else {
         return NULL;
     }
-- 
1.8.3.1