Bluetooth: Mesh: Refactor Mesh Model Extensions

The existing extension tree does not support all the features that are
defined by the specification (e.g. multiple parents).

This patch approaches this problem by defining a circular single-linked
list of extension models. So for a given model, all models that are on
the same list as that model are in some extension relationship with that
model. All models on a list represent a single connected component of an
extension graph but without defining specific relationships between each
pair of models. This list is used to manage a shared subscription list
as per the Mesh Profile Specification:

```4.2.4 Subscription List

Within an element, each model has a separate instance of a Subscription
List, unless the model extends another model on that element. Instances
of models that extend other models (i.e., all models within an extension
relation tree) shall share a single instance of a Subscription List per
element.
```

Signed-off-by: Michał Narajowski <michal.narajowski@codecoup.pl>

include/bluetooth/mesh/access.h

@@ -509,11 +509,10 @@ struct bt_mesh_model {
 	const struct bt_mesh_model_cb * const cb;
 
 #ifdef CONFIG_BT_MESH_MODEL_EXTENSIONS
-	/* Pointer to the next model in a model extension tree. */
+	/* Pointer to the next model in a model extension list. */
 	struct bt_mesh_model *next;
-	/* Pointer to the first model this model extends. */
-	struct bt_mesh_model *extends;
 #endif
+
 	/** Model-specific user data */
 	void *user_data;
 };
@@ -634,25 +633,31 @@ int bt_mesh_model_data_store(struct bt_mesh_model *mod, bool vnd,
  *  Mesh models may be extended to reuse their functionality, forming a more
  *  complex model. A Mesh model may extend any number of models, in any element.
  *  The extensions may also be nested, ie a model that extends another may
- *  itself be extended. Extensions may not be cyclical, and a model can only be
+ *  itself be extended.
- *  extended by one other model.
  *
- *  A set of models that extend each other form a model extension tree.
+ *  A set of models that extend each other form a model extension list.
  *
- *  All models in an extension tree share one subscription list per element. The
+ *  All models in an extension list share one subscription list per element. The
  *  access layer will utilize the combined subscription list of all models in an
- *  extension tree and element, giving the models extended subscription list
+ *  extension list and element, giving the models extended subscription list
  *  capacity.
  *
- *  @param mod      Mesh model.
+ *  @param extending_mod      Mesh model that is extending the base model.
- *  @param base_mod The model being extended.
+ *  @param base_mod           The model being extended.
  *
  *  @retval 0 Successfully extended the base_mod model.
- *  @retval -EALREADY The base_mod model is already extended.
  */
-int bt_mesh_model_extend(struct bt_mesh_model *mod,
+int bt_mesh_model_extend(struct bt_mesh_model *extending_mod,
 			 struct bt_mesh_model *base_mod);
 
+/** @brief Check if model is extended by another model.
+ *
+ *  @param model The model to check.
+ *
+ *  @retval true If model is extended by another model, otherwise false
+ */
+bool bt_mesh_model_is_extended(struct bt_mesh_model *model);
+
 /** Node Composition */
 struct bt_mesh_comp {
 	uint16_t cid; /**< Company ID */

subsys/bluetooth/mesh/access.c

@@ -32,7 +32,7 @@ enum {
 	BT_MESH_MOD_BIND_PENDING = BIT(0),
 	BT_MESH_MOD_SUB_PENDING = BIT(1),
 	BT_MESH_MOD_PUB_PENDING = BIT(2),
-	BT_MESH_MOD_NEXT_IS_PARENT = BIT(3),
+	BT_MESH_MOD_EXTENDED = BIT(3),
 };
 
 /* Model publication information for persistent storage. */
@@ -422,8 +422,7 @@ struct find_group_visitor_ctx {
 	uint16_t addr;
 };
 
-static enum bt_mesh_walk find_group_mod_visitor(struct bt_mesh_model *mod,
+static enum bt_mesh_walk find_group_mod_visitor(struct bt_mesh_model *mod, void *user_data)
-						uint32_t depth, void *user_data)
 {
 	struct find_group_visitor_ctx *ctx = user_data;
 
@@ -448,8 +447,7 @@ uint16_t *bt_mesh_model_find_group(struct bt_mesh_model **mod, uint16_t addr)
 		.addr = addr,
 	};
 
-	bt_mesh_model_tree_walk(bt_mesh_model_root(*mod),
+	bt_mesh_model_extensions_walk(*mod, find_group_mod_visitor, &ctx);
-				find_group_mod_visitor, &ctx);
 
 	*mod = ctx.mod;
 	return ctx.entry;
@@ -812,80 +810,74 @@ const struct bt_mesh_comp *bt_mesh_comp_get(void)
 	return dev_comp;
 }
 
-struct bt_mesh_model *bt_mesh_model_root(struct bt_mesh_model *mod)
+void bt_mesh_model_extensions_walk(struct bt_mesh_model *model,
+				   enum bt_mesh_walk (*cb)(struct bt_mesh_model *mod,
+							   void *user_data),
+				   void *user_data)
 {
-#ifdef CONFIG_BT_MESH_MODEL_EXTENSIONS
+#ifndef CONFIG_BT_MESH_MODEL_EXTENSIONS
-	while (mod->next) {
+	(void)cb(model, user_data);
-		mod = mod->next;
+	return;
+#else
+	struct bt_mesh_model *it;
+
+	if (model->next == NULL) {
+		(void)cb(model, user_data);
+		return;
 	}
-#endif
-	return mod;
-}
 
-void bt_mesh_model_tree_walk(struct bt_mesh_model *root,
+	for (it = model; (it != NULL) && (it->next != model); it = it->next) {
-			     enum bt_mesh_walk (*cb)(struct bt_mesh_model *mod,
+		if (cb(it, user_data) == BT_MESH_WALK_STOP) {
-						     uint32_t depth,
-						     void *user_data),
-			     void *user_data)
-{
-	struct bt_mesh_model *m = root;
-	int depth = 0;
-	/* 'skip' is set to true when we ascend from child to parent node.
-	 * In that case, we want to skip calling the callback on the parent
-	 * node and we don't want to descend onto a child node as those
-	 * nodes have already been visited.
-	 */
-	bool skip = false;
-
-	do {
-		if (!skip &&
-		    cb(m, (uint32_t)depth, user_data) == BT_MESH_WALK_STOP) {
 			return;
 		}
-#ifdef CONFIG_BT_MESH_MODEL_EXTENSIONS
+	}
-		if (!skip && m->extends) {
-			m = m->extends;
-			depth++;
-		} else if (m->flags & BT_MESH_MOD_NEXT_IS_PARENT) {
-			m = m->next;
-			depth--;
-			skip = true;
-		} else {
-			m = m->next;
-			skip = false;
-		}
 #endif
-	} while (m && depth > 0);
 }
 
 #ifdef CONFIG_BT_MESH_MODEL_EXTENSIONS
-int bt_mesh_model_extend(struct bt_mesh_model *mod,
+int bt_mesh_model_extend(struct bt_mesh_model *extending_mod, struct bt_mesh_model *base_mod)
-			 struct bt_mesh_model *base_mod)
 {
-	/* Form a cyclical LCRS tree:
+	struct bt_mesh_model *a = extending_mod;
-	 * The extends-pointer points to the first child, and the next-pointer
+	struct bt_mesh_model *b = base_mod;
-	 * points to the next sibling. The last sibling is marked by the
+	struct bt_mesh_model *a_next = a->next;
-	 * BT_MESH_MOD_NEXT_IS_PARENT flag, and its next-pointer points back to
+	struct bt_mesh_model *b_next = b->next;
-	 * the parent. This way, the whole tree is accessible from any node.
+	struct bt_mesh_model *it;
-	 *
+
-	 * We add children (extend them) by inserting them as the first child.
+	base_mod->flags |= BT_MESH_MOD_EXTENDED;
-	 */
+
-	if (base_mod->next) {
+	if (a == b) {
-		return -EALREADY;
+		return 0;
 	}
 
-	if (mod->extends) {
+	/* Check if a's list contains b */
-		base_mod->next = mod->extends;
+	for (it = a; (it != NULL) && (it->next != a); it = it->next) {
+		if (it == b) {
+			return 0;
+		}
+	}
+
+	/* Merge lists */
+	if (a_next) {
+		b->next = a_next;
 	} else {
-		base_mod->next = mod;
+		b->next = a;
-		base_mod->flags |= BT_MESH_MOD_NEXT_IS_PARENT;
+	}
+
+	if (b_next) {
+		a->next = b_next;
+	} else {
+		a->next = b;
 	}
 
-	mod->extends = base_mod;
 	return 0;
 }
 #endif
 
+bool bt_mesh_model_is_extended(struct bt_mesh_model *model)
+{
+	return model->flags & BT_MESH_MOD_EXTENDED;
+}
+
 static int mod_set_bind(struct bt_mesh_model *mod, size_t len_rd,
 			settings_read_cb read_cb, void *cb_arg)
 {

subsys/bluetooth/mesh/access.h

@@ -19,12 +19,10 @@ struct bt_mesh_elem *bt_mesh_elem_find(uint16_t addr);
 
 bool bt_mesh_has_addr(uint16_t addr);
 
-struct bt_mesh_model *bt_mesh_model_root(struct bt_mesh_model *mod);
+void bt_mesh_model_extensions_walk(struct bt_mesh_model *root,
-void bt_mesh_model_tree_walk(struct bt_mesh_model *root,
+				   enum bt_mesh_walk (*cb)(struct bt_mesh_model *mod,
-			     enum bt_mesh_walk (*cb)(struct bt_mesh_model *mod,
+							   void *user_data),
-						     uint32_t depth,
+				   void *user_data);
-						     void *user_data),
-			     void *user_data);
 
 uint16_t *bt_mesh_model_find_group(struct bt_mesh_model **mod, uint16_t addr);
 

subsys/bluetooth/mesh/cfg_srv.c

@@ -1145,8 +1145,7 @@ send_status:
 				   mod_id, vnd);
 }
 
-static enum bt_mesh_walk mod_sub_clear_visitor(struct bt_mesh_model *mod,
+static enum bt_mesh_walk mod_sub_clear_visitor(struct bt_mesh_model *mod, void *user_data)
-					       uint32_t depth, void *user_data)
 {
 	if (IS_ENABLED(CONFIG_BT_MESH_LOW_POWER)) {
 		bt_mesh_lpn_group_del(mod->groups, ARRAY_SIZE(mod->groups));
@@ -1206,8 +1205,7 @@ static int mod_sub_overwrite(struct bt_mesh_model *model,
 
 
 	if (ARRAY_SIZE(mod->groups) > 0) {
-		bt_mesh_model_tree_walk(bt_mesh_model_root(mod),
+		bt_mesh_model_extensions_walk(mod, mod_sub_clear_visitor, NULL);
-					mod_sub_clear_visitor, NULL);
 
 		mod->groups[0] = sub_addr;
 		status = STATUS_SUCCESS;
@@ -1269,8 +1267,7 @@ static int mod_sub_del_all(struct bt_mesh_model *model,
 		goto send_status;
 	}
 
-	bt_mesh_model_tree_walk(bt_mesh_model_root(mod), mod_sub_clear_visitor,
+	bt_mesh_model_extensions_walk(mod, mod_sub_clear_visitor, NULL);
-				NULL);
 
 	if (IS_ENABLED(CONFIG_BT_SETTINGS)) {
 		bt_mesh_model_sub_store(mod);
@@ -1288,8 +1285,7 @@ struct mod_sub_list_ctx {
 	struct net_buf_simple *msg;
 };
 
-static enum bt_mesh_walk mod_sub_list_visitor(struct bt_mesh_model *mod,
+static enum bt_mesh_walk mod_sub_list_visitor(struct bt_mesh_model *mod, void *ctx)
-					      uint32_t depth, void *ctx)
 {
 	struct mod_sub_list_ctx *visit = ctx;
 	int count = 0;
@@ -1365,8 +1361,7 @@ static int mod_sub_get(struct bt_mesh_model *model,
 
 	visit_ctx.msg = &msg;
 	visit_ctx.elem_idx = mod->elem_idx;
-	bt_mesh_model_tree_walk(bt_mesh_model_root(mod), mod_sub_list_visitor,
+	bt_mesh_model_extensions_walk(mod, mod_sub_list_visitor, &visit_ctx);
-				&visit_ctx);
 
 send_list:
 	if (bt_mesh_model_send(model, ctx, &msg, NULL, NULL)) {
@@ -1425,8 +1420,7 @@ static int mod_sub_get_vnd(struct bt_mesh_model *model,
 
 	visit_ctx.msg = &msg;
 	visit_ctx.elem_idx = mod->elem_idx;
-	bt_mesh_model_tree_walk(bt_mesh_model_root(mod), mod_sub_list_visitor,
+	bt_mesh_model_extensions_walk(mod, mod_sub_list_visitor, &visit_ctx);
-				&visit_ctx);
 
 send_list:
 	if (bt_mesh_model_send(model, ctx, &msg, NULL, NULL)) {
@@ -1639,8 +1633,7 @@ static int mod_sub_va_overwrite(struct bt_mesh_model *model,
 
 		status = bt_mesh_va_add(label_uuid, &sub_addr);
 		if (status == STATUS_SUCCESS) {
-			bt_mesh_model_tree_walk(bt_mesh_model_root(mod),
+			bt_mesh_model_extensions_walk(mod, mod_sub_clear_visitor, NULL);
-						mod_sub_clear_visitor, NULL);
 			mod->groups[0] = sub_addr;
 
 			if (IS_ENABLED(CONFIG_BT_SETTINGS)) {